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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Integrated pest management reviews 4 (1999), S. 127-143 
    ISSN: 1572-9745
    Keywords: wheat ; stored-grain ; integrated pest management ; aeration ; biological control ; grain sampling ; insect monitoring ; modeling ; area-wide IPM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Management of stored-grain insect pests by farmers or elevator managers should be based upon a knowledge of the grain storage environment and the ecology of insect pests. Grain storage facilities and practices, geographical location, government policies, and marketing demands for grain quality are discussed as factors influencing stored-grain insect pest management decisions in the United States. Typical practices include a small number of grain samples designed to provide grain quality information for segregation, blending and marketing. This low sampling rate results in subjective evaluation and inconsistent penalties for insect-related quality factors. Information on the efficacy of insect pest management practices in the United States, mainly for farm-stored wheat, is discussed, and stored-grain integrated pest management (IPM) is compared to field-crop IPM. The transition from traditional stored-grain insect pest control to IPM will require greater emphasis on sampling to estimate insect densities, the development of sound economic thresholds and decision-making strategies, more selective use of pesticides, and greater use of nonchemical methods such as aeration. New developments in insect monitoring, predictive computer models, grain cooling by aeration, biological control, and fumigation are reviewed, their potential for improving insect pest management is discussed, and future research needs are examined.
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  • 2
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    Integrated pest management reviews 4 (1999), S. 21-37 
    ISSN: 1572-9745
    Keywords: carrot weevil ; IPM ; Anaphes spp. ; biological control ; ecology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The carrot weevil, Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae) is a major pest of carrots in northeastern North America. The females oviposit in the leaf petiole and the developing larvae make tunnels in the carrot roots. Exclusive reliance on chemical control and the poor control obtained, prompted, in the early 1980s, research on the ecology and physiology of the pest and its natural enemies. Carrot weevil females start their oviposition by 147±9 DD7°C but they oviposit only in carrots past the 4 true-leaf-stage. As a result, oviposition is delayed, and damage reduced, in late-sown carrots. Monitoring carrot weevil adults in the spring with either carrot root sections or wooden plate traps enables growers to apply control treatments only if the population density justifies it. Egg parasitoids of the genus Anaphes (Hymenoptera: Mymaridae) are the most important natural enemies and they account, in untreated plots, for up to 80% mortality. Their effectiveness could be improved by managing field borders to establish secondary host species. An IPM programme was developed in the 1980s based on the research results obtained and, through regular monitoring, has achieved a substantial decrease in pesticide use.
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  • 3
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    Springer
    Integrated pest management reviews 4 (1999), S. 39-52 
    ISSN: 1572-9745
    Keywords: Scapteriscus ; Neocurtilla ; Gryllotalpa ; biological control ; turf ; pastures ; vegetables
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract There are at least 70 species of mole crickets (Orthoptera: Gryllotalpidae). Some are rare, others are innocuous, and a few are important pests. These soil-dwelling pests damage underground parts of a long list of cultivated plants. Although tillage and flooding are used successfully in some situations to bring these pests to the soil surface and expose them to vertebrate and other predators, chemical pesticides are widely used against them. Knowledge of their life history is used to time application of chemical treatments to save money, but is not used as widely as it might be. Classical biological control has been used against immigrant mole crickets in Hawaii, Puerto Rico, and the southern USA. In Florida, three Scapteriscus species from South America cause major damage to pastures and turf and are targets of a classical biological control program. Population levels of two of the pest species have been reduced substantially in Florida by establishment of a tachinid fly (Ormia depleta) and a steinernematid nematode (Steinernema scapterisci) from South America. The nematode also functions as a biopesticide. Managers of pastures and turf in Florida have thus far derived benefit from these classical biological control agents without understanding their function: use of chemicals is reduced when mole cricket populations are lower due to action of these organisms. Future enhancement of the action of O. depleta and of a sphecid wasp (Larra bicolor, which also was introduced from South America) probably will demand deliberate planting of nectar sources for adults of these biological control agents, and the advantage will be to managers who adopt such a strategy. Chemical pesticide use is strongly promoted by a large chemical industry, whereas biopesticidal use has thus far been little promoted and sales have been few. Even managers who do not change their simple strategy of pesticide use in response to damage by mole crickets, and have no knowledge of the differing life cycles of the three Scapteriscus species or of the presence and action of the classical biological control agents, will derive benefit as these biological control agents (and a predatory beetle which has not yet been released) increase their distribution.
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  • 4
    Electronic Resource
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    Integrated pest management reviews 4 (1999), S. 97-126 
    ISSN: 1572-9745
    Keywords: agriculture ; biological control ; campaign ; chemosterilent ; commensal ; control methods ; economics ; environmental and cultural methods ; horticulture ; India ; pest management ; pre- and post-harvest crop losses ; poultry farms ; rodent ; rodenticide ; South Asia ; trapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Eighteen species of rodents are pests in agriculture, horticulture, forestry, animal and human dwellings and rural and urban storage facilities in India. Their habitat, distribution, abundance and economic significance varies in different crops, seasons and geographical regions of the country. Of these, Bandicota bengalensis is the most predominant and widespread pest of agriculture in wet and irrigated soils and has also established in houses and godowns in metropolitan cities like Bombay, Delhi and Calcutta. In dryland agriculture Tatera indica and Meriones hurrianae are the predominant rodent pests. Some species like Rattus meltada, Mus musculus and M. booduga occur in both wet and dry lands. Species like R. nitidus in north-eastern hill region and Gerbillus gleadowi in the Indian desert are important locally. The common commensal pests are Rattus rattus and M. musculus throughout the country including the islands. R. rattus along with squirrels Funambulus palmarum and F. tristriatus are serious pests of plantation crops such as coconut and oil palm in the southern peninsula. F. pennanti is abundant in orchards and gardens in the north and central plains and sub-mountain regions. Analysis of the information available on the damage and economic losses caused by rodents in rice, wheat, sugarcane, maize, pearl millet, sorghum, oil seed, legume and vegetable crop fields, horticulture and forestry, poultry farms, and rural and urban dwellings and storage facilities clearly shows that chronic damage ranging from 2% to 15% persists throughout the country and severe damage, sometimes even up to 100% loss of the field crop, is not rare. Several traditional and modern approaches and methods of rodent control are being used. The existing knowledge of the environmental, cultural, biological, mechanical and chemical methods of rodent control in India is reviewed. Considerable variations exist in the susceptibility of the pest species to different methods, particularly to rodenticides and trapping, their field applicability, efficacy and economics in different crops, seasons and geographical regions, behavioural responses of the pest species to these methods in different ecological conditions and their adoption by farmers in different regions of India. Environmental and cultural techniques, such as clean cultivation, proper soil tillage and crop scheduling, barriers, repellents and proofing which may reduce rodent harbourage, food sources and immigration have long lasting effects but are seldom adopted. However, their significance in relation to normal agricultural practices, intensification and diversification are discussed. Rodenticides, which provide an immediate solution to the rodent problem, form the major component of rodent control strategies in India. Poison baiting of rodents with zinc phosphide and burrow fumigation with aluminium phosphide are common in agricultural fields and recently Racumin (coumatetralyl) and bromadiolone have been introduced for the control of both agricultural and commensal rodent pests in India. Methods and timings of campaigns and successes and problems in implementation of rodent control are also reviewed.
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  • 5
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    Integrated pest management reviews 4 (1999), S. 307-312 
    ISSN: 1572-9745
    Keywords: microbial control ; biological control ; biopesticide ; mycopesticide ; Metarhizium ; Beauveria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Microbial control agents generally kill insects more slowly than chemical pesticides, and fast-moving migratory pests may not at first sight appear to offer the most promising targets for microbial control. Operators responsible for control may need to have recourse to chemical control agents. Nevertheless, there are many occasions when pests breed and feed outside the crop and a microbial control agent can be used. Similarly, immature stages may cause little damage and early treatment in the crop can avoid damage. Microbial control agents are particularly likely to be favoured if the pest breeds in a conservation area, and if a publicly-accountable agency is responsible for control. Other key points of importance are the IPM context, in particular detection, planning and forecasting of outbreaks and the role of natural enemies. With these points in mind, we identify several locust and grasshopper systems where microbial control is becoming established; additionally, Sunn pest of wheat and Armyworm are identified as promising situations forbreak microbials.
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  • 6
    ISSN: 1871-4528
    Keywords: bioassay ; biological control ; blackleg ; green crop harvesting ; haulm killing ; skin damage ; wound protection ; Solanum tuberosum L
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Green crop lifting (GCL) for haulm killing was developed in The Netherlands and offers ideal conditions for controlling the blackleg pathogenErwinia carotovora subsp.atroseptica (Eca) by antagonists. Based on the use of mini-tubers or young tubers from field crops, two bioassays for wound protection were developed. GCL was simulated by artificially skinning or wounding tubers, inoculating the damaged skin with Eca, treating with antagonists and incubating in either potting compost or outside in field soil. Mainly fluorescent pseudomonads, pre-screened for in vitro antagonistic activity on agar and high soft rot reducing ability on tuber slices, were tested in the mini-tuber bioassay. Strains giving the highest degree of wound protection were further tested individually and in combination under field conditions in the young tuber bioassay. One individual strain and two combinations, resulting in reduction of contamination levels on skinned surfaces of 85% and between 60% and 70%, respectively, show good potential for biological control of blackleg.
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  • 7
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    European journal of plant pathology 105 (1999), S. 123-137 
    ISSN: 1573-8469
    Keywords: Aureobasidium pullulans ; biological control ; Cryptococcus albidus ; grey mould ; Trichoderma harzianum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The efficacy of Trichoderma harzianum T39 and the yeasts Aureobasidium pullulans and Cryptococcus albidus against Botrytis cinerea in cucumber and tomato was compared with chemical control. Four experiments were conducted in cucumber grown under different climatic conditions in The Netherlands, and two experiments were done in tomato both in the Netherlands and in Israel. T. harzianum and A. pullulans showed the most consistent control of B. cinerea, reducing stem lesions and death of plants by 40–100% in most cases. Control of stem lesions and subsequent wilting was generally better than control of symptoms on fruits. In some cases, the biocontrol agents were more effective than the broad-spectrum fungicide tolylfluanid and the selective fungicide iprodione. The climatic conditions did not strongly influence the efficacy of the biocontrol agents, but regression analysis showed that high temperature during the day and high vapour pressure deficit during the night reduced biocontrol efficacy. From the results, prospects for biocontrol of B. cinerea in greenhouse vegetables appear good under a range of conditions.
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  • 8
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    European journal of plant pathology 105 (1999), S. 95-101 
    ISSN: 1573-8469
    Keywords: bacteria ; biological control ; Chryseobacterium ; Flavobacterium ; grey mold ; Pseudomonas ; strawberries
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Most potential fungal antagonists have been identified only after exhaustive non-selective screening. Bacteria antagonistic to Botrytis cinerea were selected using a simple method based on techniques developed for trace enrichment studies, where a crude cell wall preparation from B. cinerea was used as a selective substrate and bacteria were isolated based on growth on cell wall agar media. Most of the 52 bacterial isolates that were obtained from the surface of ‘organically grown’ strawberry fruit and could grow on B. cinerea wall media in culture showed some ability to inhibit the growth of the fungus. Potato dextrose agar seeded with B. cinerea spores (104 ml−1) were challenged with each of these bacterial isolates at concentrations of 109 and 106 colony forming units ml−1. Eleven of the 52 isolates initially recovered, subsequently demonstrated strong antagonism in vitro and were selected for additional screening tests on strawberry fruit. All 11 isolates reduced grey mold rot incidence on fruit in storage. Three of the best isolates were tested in limited field trials, and also reduced grey mold rot on fruit under field conditions.
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  • 9
    ISSN: 1573-8469
    Keywords: in vitro interactions ; biological control ; rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Fusarium wilt diseases, caused by the fungus Fusarium oxysporum, lead to significant yield losses of crops. One strategy to control fusarium wilt is the use of antagonistic, root-colonizing Pseudomonas spp. It has been demonstrated that different strains of these bacteria suppress disease by different mechanisms. Therefore, application of a mixture of these biocontrol strains, and thus of several suppressive mechanisms, may represent a viable control strategy. A prerequisite for biocontrol by combinations of biocontrol agents can be the compatibility of the co-inoculated micro-organisms. Hence, compatibility between several Pseudomonas spp. strains, that have the ability to suppress fusarium wilt of radish, was tested in vitro on KB agar plates. Growth of P. fluorescens strain RS111 was strongly inhibited by Pseudomonas spp. strains RE8, RS13, RS56 and RS158, whereas a mutant of strain RS111 (RS111-a) was insensitive to inhibition by these strains. Strains RS111 and RS111-a only slightly inhibited some other strains. Suppression of fusarium wilt of radish in a potting soil bioassay by the incompatible combination of RE8 and RS111 was comparable to the effects of the single strains. However, disease suppression by the compatible combination of RE8 and RS111-a was significantly better as compared to the single strains. In contrast, the incompatible combination of RS56 with RS111 resulted in enhanced disease suppression as compared to the single strains. Increased disease suppression by combinations of RS13 or RS158 with RS111 or RS111-a was not observed. This indicates that specific interactions between biocontrol strains influence disease suppression by combinations of these strains.
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  • 10
    ISSN: 1573-8469
    Keywords: Alternaria brassicae ; biological control ; cross infection ; disease management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Resistance in susceptible mustard cv. PR-15 against the highly virulent A. brassicae isolate A (AbA) and moderately virulent isolate C (AbC) was induced using an avirulent Alternaria brassicae isolate D (AbD). The induction of resistance due to AbD against AbA or AbC resulted in significant reduction in disease severity. The A. alternata (Aa) failed to induce resistance against AbA and AbC, on the contrary it induced susceptibility against them.
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  • 11
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    European journal of plant pathology 105 (1999), S. 177-189 
    ISSN: 1573-8469
    Keywords: biological control ; grey mould ; mechanisms ; pathogenicity enzymes ; proteolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The role of protease of Trichoderma harzianum in the biocontrol of Botrytis cinerea was examined. Two isolates of T. harzianum were compared for their ability to produce protease in liquid culture medium and on the surface of bean leaves. The biocontrol agent T. harziaum T39 produced 58 mU/ml of protease and T. harzianum NCIM1185 produced 54 mU/ml on the 5th day of growth in liquid culture medium. On bean leaves, combinations of B. cinerea and T. harzianum isolates were examined for the synthesis of protease. The protease activities were 0.9 and 0.6 mU/ml for T. harzianum T39 and NCIM1185, respectively, and 0.5 mU/ml for B. cinerea alone after 48 h of incubation. In the presence of T. harzianum T39 culture liquid containing protease, a 55% reduction in B. cinerea germination and a 80% reduction in the germ tube length were observed after 17 h of incubation in vitro. When T. harzianum isolates were added to B. cinerea on bean leaves, increased synthesis of protease was observed (1.0 and 1.2 mU/ml for T39 and NCIM1185, respectively). In the presence of T. harzianum NCIM1185 protease, although the rate of germination was reduced, B. cinerea attained 98% germination after 17 h of incubation. The hydrolytic enzymes produced by B. cinerea, endo-polygalacturonase (PG) and exoPG were partially deactivated by protease from the T. harzianum isolates. Carboxymethyl cellulase was deactivated only by protease of NCIM1185. On the surface of bean leaves, the protease (obtained from liquid culture medium of T. harzianum isolates) resulted in 56–100% reduction of disease severity. The culture liquid containing protease synthesized on the surface of bean leaves treated with B. cinerea and with T. harzianum was collected and added to fresh leaves infected by B. cinerea. There was 56–100% and 30–75% reduction of disease severity with liquid droplet collected from the leaves treated with T. harzianum T39 and NCIM1185, respectively. Increased control of disease was obtained by combining the conidia of T. harzianum isolates with protease obtained from culture media. Protease inhibitors, trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane (E64), antipain hydrochloride, and a mixture of inhibitors, but not pepstatin A, fully or partially nullified the biocontrol effect of T39. T39 was found to be a poor producer of chitinase and β-1,3-glucanase in vitro. These enzymes were not detected on leaves treated with T39. Involvement of protease in biocontrol of B. cinerea is suggested.
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  • 12
    ISSN: 1573-8248
    Keywords: Acari ; biological control ; generalist ; intraspecific predation ; multiple species release ; predatory mites ; specialist
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We examined intra- and interspecific predation of adult females and immature stages of the generalist Neoseiulus californicus and the specialist Phytoseiulus persimilis. Adult females and immatures of both predators exhibited higher predation rates on larvae than on eggs and protonymphs. N. californicus fed more inter- than intraspecifically. Predation on P. persimilis by N. californicus was more severe than vice versa. P. persimilis had higher predation rates on conspecifics than heterospecifics and was more prone to cannibalism than N. californicus. When provided with phytoseiid prey, P. persimilis suffered higher mortality than N. californicus. When held without food, adult females and protonymphs of N. californicus survived longer than the corresponding stages of P. persimilis. N. californicus females were able to sustain oviposition when preying upon P. persimilis, whereas cannibalizing females did not lay eggs. Females of P. persimilis were not able to sustain oviposition, irrespective of con- or heterospecific prey. Immatures of both predators were able to reach adulthood when provided with either con- or heterospecifics. Juvenile development of N. californicus was shorter with heterospecific vs. conspecific larvae; mortality of P. persimilis immatures was less when feeding on conspecific vs. heterospecific larvae. Different behavioral pattern in intra- and interspecific predation are discussed in regard to their feeding types (generalist vs. specialist).
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  • 13
    ISSN: 1573-8248
    Keywords: biological control ; Botrytis aclada ; Botrytis cinerea ; cyclamen ; ecological adaptation ; hydrangea ; lily ; onion ; temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Ulocladium atrum and Gliocladium roseum are fungal antagonists capable of suppressing sporulation of Botrytis spp. on dead plant parts. The effect of temperature (3 to 36 °C) on antagonist conidial germination and mycelial growth was assessed on agar. In addition conidial germination of U. atrum was measured on dead lily leaves. The optimum temperature of both antagonists for both conidial germination and mycelial growth was between 27 and 30 °C. U. atrum was less affected by lower temperatures than G. roseum. At optimum temperature, 50% of conidia of U. atrum and G. roseum germinated within 2.6 and 10.0 hrs, respectively. At low sub-optimal temperatures (6 °C), 50% of conidia germinated within 18 and 96 hours, respectively. In bioassays on dead onion leaves, U. atrum suppressed sporulation of B. cinerea and B. aclada at all temperatures tested (6 to 24 °C) by more than 85%. On dead cyclamen leaves, G. roseum was more efficient than U. atrum at 21 and 24 °C but, in contrast to U. atrum, showed no antagonistic activity at temperatures below 21 °C. On dead hydrangea leaves, U. atrum significantly reduced sporulation of B. cinerea at temperatures as low as 3 and 1 °C. Under Dutch growing conditions, the mean air temperature during leaf wetness periods in onion and lily fields was 15 °C with temperatures only occasionally above 20 °C. In greenhouse crops of cyclamen, the mean temperature during high humidity periods was 17 °C. It is therefore concluded that U. atrum is better adapted than G. roseum to temperatures which occur in the field, in greenhouse crops such as cyclamen, or during cold storage of plant stocks.
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  • 14
    ISSN: 1573-8248
    Keywords: Anaxipha longipennis ; biological control ; Gryllidae ; Metioche vitatticollis ; parasitism ; predation ; Trichogramma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Egg mortality of rice leaf folders Cnaphalocrocis medinalisand Marasmia patnalis was studied in unsprayed irrigated rice fields in Laguna Province, the Philippines. Mortality was assessed by field exposure of laboratory-laid eggs for two days and by monitoring of field-laid eggs. Egg disappearance, the major mortality factor, was low in the first four weeks after transplanting and then increased. Egg parasitism by Trichogrammajaponicum was highest at the start of the crop and decreased to a low level towards crop maturity. Non-hatching of eggs was of minor importance. Over the total duration of the egg stage, the average disappearance of exposed laboratory-laid eggs was40%, and of field-laid eggs 46%. Egg mortality due to parasitism averaged 15% and 18%, respectively. The potential impact of egg parasitism is probably partly obscured by the disappearance of parasitized eggs. Mortality rates were highly variable between egg cohorts, but with multiple regression analysis several factors were identified that statistically explained a significant part of this variation. The results suggest that the predatory crickets Metiochevittaticollis and Anaxipha longipennis play a major role in egg disappearance, and that egg parasitism is positively dependent on the overall density of host eggs of Trichogramma in the field.
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  • 15
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    BioControl 44 (1999), S. 159-169 
    ISSN: 1573-8248
    Keywords: biological control ; Euphorinae ; species identification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Four parasitoids of the subfamily Euphorinae are common in New Zealand pasture. These are Microctonus aethiopoides, M. hyperodae, M. zealandicus and Dinocampus coccinellae. There is overlap in these parasitoids' host ranges and, although adults of these species can be identified morphologically, their larval stages have not yet been compared. This contribution provides morphological descriptions of the head capsules of 1st instar larvae that enable the four parasitoid species to be distinguished. Diagnostic characteristics are the shape of the mandible and the pattern of sclerotisation on the hypopharynx. Post 1st instar larvae can be identified by retrieving the shed 1st instar head capsule from the host abdomen.
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  • 16
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    BioControl 44 (1999), S. 347-367 
    ISSN: 1573-8248
    Keywords: Aphidiidae ; biological control ; Chrysopidae ; Coccinellidae ; entomopathogens ; Hemerobiidae ; Syrphidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Sixteen cohorts of the brown citrus aphid, Toxoptera citricida, were followed from colony initiation to maturation/extinction in citrus groves at two sites in Puerto Rico and nine sites in Florida, USA. Infested citrus terminals were sampled repeatedly in a non-destructive manner and data recorded on the recruitment of natural enemies and the fate of aphid colonies. Coccinellidae were the most efficient predators of T. citricida, primarily Cycloneda sanguinea, and Coelophora inaequalis (Puerto Rico), C. sanguinea, Harmonia axyridis (Florida). Coccinellids were abundant in citrus year-round in Puerto Rico, but in Florida citrus their abundance peaked in spring and declined thereafter. Syrphid flies were other important predators, especially Pseudodorus clavatus (Florida and Puerto Rico) and Ocyptamus fuscipennis (Puerto Rico). Syrphids increased in abundance from spring to fall in both regions. Other predators included Cereaochrysa lineaticornis, Chrysoperla rufilabris (Chrysopidae) and Micromus posticus (Hemerobiidae). The parasitoid Lysiphlebus testaceipes was ubiquitous in T. citricida cohorts, but its impact on colony survival was usually low. The fungal pathogen Verticillium lecanii was a significant source of colony mortality at one site in Puerto Rico, but was not observed on T. citricida in Florida.
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  • 17
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    BioControl 44 (1999), S. 291-299 
    ISSN: 1573-8248
    Keywords: biological control ; cerambycid ; Coleoptera ; pine wood borer ; poplar wood borer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Artificial diets for the colydiid beetle, Dastarcus helophoroides, a predator of cerambycid beetles and xylocopid bees, were evaluated. Hatched larvae were reared on artificial diets composed of silkworm pupa-powder, dry yeasts, yeast extract, sucrose, peptone, squid liver oil, preservatives and distilled water, but their emergence rate was very low. If larvae were fed paralyzed cerambycid larvae till they became approximately 8 mm in body length and then reared on artificial diet, emergence rates were high. Using the latter method, mass-production of this colydiid beetle is feasible.
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  • 18
    ISSN: 1573-8248
    Keywords: bacterial antagonists ; biological control ; Pantoea agglomerans ; pseudosclerotia ; Sclerotiniaceae ; Vaccinium macrocarpon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Bacteria inhibitory to Moniliniaoxycocci, the cranberry cotton ball pathogen, were identified. Eighty-three bacteria isolated from a cranberry marsh and Erwinia herbicola C9-1,which is being developed elsewhere for the biological control of fire blight of pome fruits, were tested fortheir ability to inhibit radial growth and conidial germination of M. oxycocci in vitro. IsolateBA35 from cranberry (tentatively identified as Pseudomonas syringae pv. morsprunorum) and E. herbicola C9-1 completely inhibited radial growth of M. oxycocci. BA35 and C9-1 were among the most effective of 21 bacteria tested for inhibition of conidial germination. Growth of bacteria in sclerotial extracts of M. oxycocci and Sclerotinia sclerotiorum was determined in order to select isolates that might be successful in degradingsclerotia, thereby reducing the viability of M.oxycocci. Populations of isolates 62 and S-18(identities unknown), and S-19 (tentatively identified as Micrococcus luteus), increased approximately3.0--5.0 log10 units in all extracts within 24 h. Populations of isolate S-10 increased by about 3.5log10 units in all sclerotial extracts within 48 h. Populations of isolate S-49 (identity unknown)were lower in extracts of M. oxycocci than S. sclerotiorum after 48-h. In buffer controls, bacterial populations remained stable or decreased over the 48-h period.
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  • 19
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    BioControl 43 (1999), S. 441-456 
    ISSN: 1573-8248
    Keywords: agroecosystems ; biological control ; Carabidae ; carabid community ; Coleoptera ; generalist predators ; natural enemy abundance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Generalist natural enemies such as carabid beetles have the potential to maintain a variety of pests below outbreak levels in annual crops. To assess the relationship between carabid beetle abundance and field rates of prey removal, we created plots surrounded by different boundaries that selectively affected dispersal of edaphic arthropods, primarily carabids. Three treatments were established: (1) naturally occurring communities, (2) augmented communities using ingress boundaries, and (3) reduced communities using egress boundaries. Selective boundaries altered carabid communities with minimal habitat alteration and without use of insecticides. Three times during the growing season, a fixed number of onion fly pupae were placed in plots to evaluate the impact of carabid abundance on predation rates. A combination of vertebrate and invertebrate exclosures allowed us to evaluate prey removal by invertebrates alone. In comparison to the no boundary treatment, carabids increased 54.2% and decreased 83.1% in plots surrounded by ingress and egress boundaries respectively. Predation rates were positively correlated with carabid abundance (r2 = 0.70, p 〈 0.0001). Significantly more pupae were removed from exclosures allowing access to invertebrates alone than from total exclosures, suggesting that invertebrates represented an important group of predators. Laboratory trials tested the feeding potential of the four most abundant carabid species and showed that they readily consumed onion fly pupae, supporting our hypothesis that carabids were the main predators in field tests. This study corroborates and extends previous observations of the importance of carabid beetles as generalist predators of insect pests in agricultural fields.
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  • 20
    ISSN: 1573-8248
    Keywords: Acari ; biological control ; cannibalism ; generalist ; interspecific predation ; multiple predators release ; predatory mites ; specialist
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Discrimination between and predation preference for con- or heterospecific larvae was examined for adult females of P. persimilis and N. californicus in plexiglass cages with and without their primary prey T. urticae. Rates of intra- and interspecific predation on larvae were measured for females held on leaves and provided with excess amounts of spider mites. Females of the generalist N. californicus distinguished con- and heterospecific larvae and preferred to prey upon the latter. Females of the specialist P. persimilis appeared to lack discrimination ability and fed equally on con- and heterospecifics. When spider mites and phytoseiids were offered simultaneously, all P. persimilis females chose to first attack T. urticae, whereas N. californicus females attacked both tetranychids and heterospecific phytoseiids. Females of both predators preyed upon phytoseiid larvae when held on leaves with surplus T. urticae: while P. persimilis fed on both con- and heterospecifics, N. californicus attacked larvae of P. persimilis but avoided cannibalizing larvae. The different behaviors of P. persimilis and N. californicus are discussed with regard to different predation types (generalists vs. specialists) and the possible consequences of mixed release for biological control of spider mites in greenhouses.
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  • 21
    ISSN: 1573-8248
    Keywords: biological control ; kaolin ; mycoherbicide ; preservation ; weed
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Different solid substrates were investigated as spore production methods for Stagonospora convolvulistrain LA39, a potential bioherbicide for field bindweed (Convolvulusarvensis L.). Up to 4 × 108 spores/g of substratewere yielded on cous-cous (cracked hard wheat). Thespores were as pathogenic as those grown on artificial medium (V-8-juice agar). The air-drying on kaolin and storage at 3 °C kept spores viable and pathogenic for 180 days. Spore germination exceeded70% for the first 140 days and then declined to 50%after 175 days. Less than 5% of spores were still viable after 17 months. The preservation of stock cultures in 10% glycerine at −80 ° C and in liquid nitrogen did not affect viability orpathogenicity of the spores.
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  • 22
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    Integrated pest management reviews 3 (1998), S. 111-116 
    ISSN: 1572-9745
    Keywords: stored product mites ; biological control ; history ; predators ; prey
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A history of the biological control of stored product mites is reviewed. Thirty-five references in the scientific literature were found principally dealing with acarine predators. The first paper to point out the specific value of Cheyletus eruditus as a predator of acaroid mites appeared in 1912. In 1965 biological control utilizing C. eruditus was put into practice for the first time and in 1986 a method of mass rearing the predator was developed.
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  • 23
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    Integrated pest management reviews 3 (1998), S. 63-83 
    ISSN: 1572-9745
    Keywords: Biosteres ; Coptera ; Diachasmimorpha ; Psyttalia ; Tetrastichus ; augmentation ; host habitat location ; dispersal ; behavioural ecology ; biological control ; classical biological control ; integrated pest management ; mass rearing ; quality control ; parasitoids ; tephritidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The biological control of pest tephritid flies using parasitoids has been successful in relatively few subtropical and tropical regions. The best documented successes were in Hawaii and Florida, USA, Fiji and southern Europe. There were relatively limited successes in Australia, Costa Rica and Mexico. With the accidental establishment of new pest tephritids, such as Bactrocera latifrons (Hendel) in Hawaii or Bactrocera papayae Drew and Hancock in Australia, foreign exploration for new parasitoids is essential. A renewal of interest in classical biological control has recently occurred, although not at the same level as in the 1940s and 1950s. New parasitoid species are currently being obtained for several tephritids, such as Ceratitis capitata (Weidemann), B. latifrons and Anastrepha suspensa (Loew). The advances in mass rearing and quality control technology for parasitoids has enabled researchers to perform large-scale field testing of these parasitoids to determine the potential of augmentative releases. Numerous studies on the augmentative release of parasitoids have been done. Historically, the larval—pupal parasitoid Diachasmimorpha longicaudata (Ashmead) has been the most frequently studied parasitoid, due to the ease of rearing this species. However, recent successes in rearing other species with different biologies, e.g. the egg—pupal parasitoid Biosteres arisanus (Sonan), the gregarious eulophid, Tetrastichus giffardianus (Silvestri) and the pupal parasitoid, Coptera sp., will enable researchers to broaden the repertoire of parasitoid species for the future. Both successes and failures in augmentative releases have occurred. Without knowledge of the behavioural ecology of parasitoids, the reasons for success or failure can only be surmised. Recent research on the dispersal and host habitat finding of tephritid parasitoids will provide insights into improving augmentation and conservation strategies. The integrated pest management (IPM) of tephritid flies in the tropics has been less well-developed than research and programmes for tephritids in temperate zones. Significant emphasis is now being placed on the development of quarantine treatment methods that are environmentally sound; thus IPM will take a larger role. Several existing pest management strategies are reviewed which show the potential for compatibility with the activities of tephritid parasitoids. These include trap cropping, insecticides with selective toxicity to the target pests, mass trapping with parapheromones, the sterile insect technique and field sanitation.
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  • 24
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    Integrated pest management reviews 3 (1998), S. 225-242 
    ISSN: 1572-9745
    Keywords: Hypera postica ; alfalfa weevil ; Medicago sativa ; alfalfa ; biological control ; classical biological control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Alfalfa weevil, Hypera postica (Gyllenhall) (Coleoptera: Curculionidae), is of Eurasian origin. This destructive pest of alfalfa (lucerne) was accidentally established in North America on three separate occasions. These introductions are commonly identified in the literature as biological strains: western alfalfa weevil, Egyptian alfalfa weevil (=Hypera brunneipennis Boheman), and eastern alfalfa weevil. Alfalfa weevil has been the target of classical biological control almost since its discovery in North America more than 90 years ago. These efforts have resulted in establishment of at least nine exotic parasitoids and egg predators: Bathyplectes curculionis (Thomson), B. anurus (Thomson) and B. stenostigma (Thomson) (Hymenoptera: Ichneumonidae); Microctonus aethiopoides Loan and M. colesi Drea (Hymenoptera: Braconidae), the latter of undetermined origin; Oomyzus incertus (Ratzenberg) (Hymenoptera: Eulophidae); Dibrachoides dynastes (Forester) and Peridesmia discus (Walker) (Hymenoptera: Pteromalidae); and Anaphes luna (Girault) (Hymenoptera: Mymaridae). A fungal pathogen, Zoophthora phytonomi Arthur (Phycomycetes: Entomophthoraceae), of undetermined origin, is becoming an increasingly important alfalfa weevil mortality factor. Most major USA alfalfa production areas now benefit from a complex of alfalfa weevil biological control agents. Collectively, these agents have effected substantial reduction in the economic importance of alfalfa weevil across the northern USA However, biological agents provide only partial control of alfalfa weevil, and importance of their contribution differs considerably with production area. Still, the benefits achieved, especially from reduced need for insecticides in alfalfa production, mark this as one of the great success stories of classical biological control in North America.
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  • 25
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    European journal of plant pathology 104 (1998), S. 29-36 
    ISSN: 1573-8469
    Keywords: biological control ; Zea mays ; Pythium spp. ; Fusarium spp. ; seed bacterization Burkholderia cepacia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Burkholderia cepacia (syn. Pseudomonas cepacia) strain PHQM100 applied as a seed coating was tested in growth chamber experiments for its ability to suppress preemergence damping-off, and postemergence damping-off in corn induced by Pythium and Fusarium spp. The symptoms observed in bioassays with soils naturally infested with the fungal pathogens were seed rot with Pythium spp. and mesocotyl and root tissue necrosis in the presence of Fusarium spp. Three corn cultivars that differed in their susceptibility to damping-off pathogens were used. Cultivar L was susceptible to pre- and postemergence damping-off, whereas cv. LPDP and cv. LG11 were moderately resistant and resistant to the damping-off diseases respectively. In the presence of Pythium spp., seed treatment with B. cepacia reduced seed rot, as compared to the untreated seeds, and this reduction was more consistent in the cv. LPDP than in the resistant cv. LG11 or the susceptible cv. L. In soils infested with Fusarium spp., seed treatment significantly reduced root and mesocotyl necrosis as compared to the untreated seeds, and this reduction was more consistent in the resistant cultivars LG11 and LPDP than in the susceptible cv. L. Root colonization levels by B. cepacia were similar in the three corn cultivars tested. Biocontrol efficiency of B. cepacia varied among cultivars mainly due to the differences in their susceptibility to the fungal pathogens. In spite of variability and also irrespective of the soil characteristics, B. cepacia increased seedling emergence and decreased mesocotyl and root necrosis when used as a seed coating.
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  • 26
    ISSN: 1573-8469
    Keywords: autoinduction ; biological control ; gene regulation ; LuxR/LuxI ; N-acyl-homoserine lactones ; fluorescent pseudomonads ; quorum sensing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract An emerging area within biological control is the role of N-acyl-homoserine lactones (N-acyl-HSL's) in the regulation of competitive fitness and pathogen suppression. N-acyl-HSL regulatory systems utilize two conserved proteins which belong to the LuxR/LuxI regulatory family: one is a transcriptional regulator and the second produces the N-acyl-HSL signal. These signals regulate the expression of a diverse range of bacterial traits involved in microbe-microbe and host-microbe interactions. Several fluorescent pseudomonads important in biological control produce N-acyl-HSL signals which regulate genes that encode products involved in pathogen suppression. In contrast to pathogenic bacteria, little is known regarding N-acyl-HSL-mediated gene regulation in biological control bacteria. This minireview will focus on the current status of the role of N-acyl-HSL's in the regulation of phenazine antibiotic and rhamnolipid production in biological control by fluorescent pseudomonads. The potential relevance of this type of regulation in biological control of plant diseases, and areas requiring further research will be addressed.
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  • 27
    ISSN: 1573-8469
    Keywords: Bacillus thuringiensis ; biological control ; Helicotylenchus multicinctus ; nematicide ; numerical response ; Paecilomyces marquandii ; Radopholus similis ; Streptomyces costaricanus ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effect of 24 treatment combinations of cultures of Streptomyces costaricanus sp. nov. (ATCC55274), Bacillus thuringiensis (ATCC55273) and a strain of Paecilomyces marquandii, nematicide (cadusaphos), and/or wheat mash on growth and response of potted banana plants (Musa AAA) and populations of Radopholus similis, Helicotylenchus multicinctus and free living nematodes were studied in Río Frío, Costa Rica. The best plant responses (height, leaf numbers, healthy root weight), lowest numbers of plant parasitic nematodes and highest numbers of free living nematodes were observed for treatments containing wheat as a component. Two treatments, viz. wheat + Streptomyces costaricanus (200-ml culture) and wheat + P. marquandii (200-ml culture), gave the overall best results. Numbers of free living nematodes increased up to 1500-fold only for treatments containing wheat. Significant positive correlations existed between numbers of free living nematodes and shoot weight, healthy root biomass, plant height, and leaf numbers. Non-wheat treatments, including nematicide only, gave the poorest responses in general. Observations of nematodes sampled 50 days following planting in wheat-containing treatments showed most of the free-living nematodes (≈ 90%) to be infected by nematophagous fungi (species not recorded). The results show that an organic amendment to soil, with or without a microbial component, can be an effective inducer of processes that regulate plant-parasitic nematode populations in soil.
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  • 28
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    European journal of plant pathology 104 (1998), S. 243-251 
    ISSN: 1573-8469
    Keywords: biological control ; Gliocladium ; field tests
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A screening system is described for identifying fungal antagonists from soil which are effective in controlling seed-borne Fusarium culmorum on wheat (T. aestivum L.). The procedure comprised three consecutive in vivo tests done under controlled conditions using three different plant growing media. Altogether 1701 fungal isolates from Finnish field soils were screened for biocontrol activity. 210 fungal isolates that had advanced to various stages in the screening system were also included in a field experiment. The isolates that were the most effective in controlling seedling blight under natural conditions belonged to the genus Gliocladium. The screening tests separated Gliocladium spp. rather clearly from the rest of test fungi and thus the overall agreement among the results was good. The assays run under controlled conditions did not efficiently predict which of the Gliocladium isolates would be best in protecting wheat seedlings under field conditions.
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  • 29
    ISSN: 1573-8469
    Keywords: biological control ; Pythium root rot of cucumber ; Pythium aphanidermatum ; rhizobacteria ; induced resistance ; Pseudomonas aureofaciens ; Pseudomonas corrugata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effect of induced systemic resistance (ISR) by Pseudomonas rhizobacteria on the pre- and post-infection development of Pythium aphanidermatum on cucumber roots was investigated. Cucumber plants (cv. Corona) were grown in vermiculite, roots were split with one side bacterized with Pseudomonas corrugata strain 13 or P. aureofaciens strain 63-28 (bacterized roots) and the other distant side was treated with water (distant, induced roots). For the non-induced control, roots on the bacterized side were treated with buffer instead of the bacterial treatment. Intact, non-split roots were also treated with the bacteria or buffer as a control. Cucumber root tissue from these treatments were harvested and incubated with a zoospore suspension of P. aphanidermatum for three hours. Most of the zoospores in the suspension were stimulated to encyst or germinate. The numbers of germinated zoospores were significantly decreased on distant induced cucumber roots in comparison to non-induced controls. Germination was also reduced on intact bacterized roots, compared to controls. There was less attachment, germ tube production and penetration on roots bacterized or induced by the rhizobacteria compared to non-induced roots. Effects were significantly greater on bacterized roots (roots colonized by bacteria) compared to distant induced roots (roots with the opposite side bacterized). Systemic resistance induced by the two Pseudomonas spp. also reduced pathogen spread on split cucumber roots in planta. Crown infection from induced or bacterized roots was delayed for four to six days in comparison to the non-induced control. Results indicated that Pseudomonas spp. can exert both an indirect influence on P. aphanidermatum zoospore behaviour and infection via induced systemic resistance (ISR) and a local influence via antibiosis or local induced resistance.
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  • 30
    ISSN: 1573-8469
    Keywords: groundnut ; lipoxygenase ; disease resistance ; biological control ; PGPR ; Bacillus subtilis ; Aspergillus niger
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Metabolic products of polyunsaturated fatty acids have been variously implicated in control of microbial pathogens. Induced resistance has been shown as one of the mechanisms of biological control by plant growth promoting rhizobacteria (PGPR). This paper reports a significant lipoxygenase (LOX) activity in groundnut seedlings with production of 13-hydroperoxyoctadecadienoic acid (13-HPODE) and 13-hydroperoxyoctadecatrienoic acid (13-HPOTrE) as major products with linoleic acid (LA) and α-linolenic acid (ALA), respectively. Both the hydroperoxides are inhibitory to the growth of Aspergillus niger as measured in micro titer plates. Ours is the first report on induction of LOX activities in groundnut on treatment with a PGPR strain Bacillus subtilis AF 1, and with crown-rot pathogen, A. niger. Treatment with B. subtilis AF 1 enhanced LOX levels in groundnut similarly but earlier to A. niger – treatment. This induction of LOX during activation of growth and pathogen infection was discussed in light of the reported involvement of LOX both in growth and development as well as in plant-pathogen interaction, particularly induced disease resistance.
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  • 31
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    European journal of plant pathology 104 (1998), S. 435-447 
    ISSN: 1573-8469
    Keywords: biological control ; conidial viability ; germination potential ; Lillium spp. microclimate ; necrosis ; saprophyte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In 1995, conidia of Ulocladium atrum were applied to a canopy of green lily (Lillium spp.) leaves in order to investigate its survival, colonisation of artificially induced necrotic leaf tissues and competitive ability against Botrytis spp. and naturally occurring saprophytes. U. atrum conidia density cm-2 at the top and middle canopy levels was not significantly different following application of the antagonist with a propane powered backpack sprayer. In repeat experiments, conidia density on leaves at the lower canopy level was 18% to 20% of that deposited onto leaves at the top of the lily canopy. There was a significant (P 〈 0.001) linear decline of U. atrum conidia over time and after 21 days conidia density had declined by up to 73%. Germination of U. atrum on green leaves in the field reached a maximum of 81%, seven days after antagonist application. Conidial viability, measured as germination potential, declined slightly (100% to 88%) after seven days exposure to field conditions but there were no further changes in the germination potential even after 21 days of field exposure. The germination potential was not affected by canopy level. The ability of surviving U. atrum conidia to colonise necrotic tissues, artificially induced with paraquat, was measured. U. atrum colonisation was consistently highest on necrotic leaves at the top level of the canopy and consistently lower on leaves from the bottom canopy level. Necrotic leaf colonisation by U. atrum decreased over time from 51% (necrosis induced immediately after antagonist application) to 21% when necrosis was induced 21 days after antagonist application. A significant (P 〈 0.001) linear relationship (R2 = 0.713) between colonisation of necrotic tissues and conidia density prior to induction of necrosis was detected. When necrosis was induced immediately after antagonist application, U. atrum outcompeted commonly occurring saprophytic Alternaria spp. and Cladosporium spp. The ability of U. atrum to significantly reduce colonisation by Alternaria spp. was maintained for up to 21 days. Botrytis spp. did not occur in these field experiments. It was concluded that U. atrum had the ability to survive and persist in the phyllosphere for up to 21 days in the field and provided further evidence that U. atrum has the necessary survival characteristics to be a successful biological control agent of Botrytis spp.
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  • 32
    ISSN: 1573-8469
    Keywords: biological control ; Fusarium oxysporum f. sp. lycopersici ; pathogenesis-related proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Fluorescent pseudomonads and nonpathogenic Fusarium oxysporum have been shown to suppress fusarium wilts. This suppression has been related to both microbial antagonism and induced resistance. The aim of the present study was to assess the relative importance of systemic induced resistance in the suppression of fusarium wilt of tomato in commercial-like conditions by a reference strain of each type of microorganism (P. fluorescens WCS417r and nonpathogenic F. oxysporum Fo47). The spatial separation of the pathogen and the biocontrol strains excluded any possible microbial antagonism and implicated the involvement of the systemic induced resistance; whereas the absence of any separation between these microorganisms allowed the expression of both mechanisms. Since systemic induced resistance has often been associated with the synthesis of PR-proteins, their accumulation in tomato plants inoculated with WCS417r or with Fo47 was determined. The analysis of the results indicates that the suppression of fusarium wilt by P. fluorescens WCS417r was ascribed to systemic induced resistance without any detection of the PR-proteins tested (PR-1 and chitinases). In contrast, the suppression achieved by nonpathogenic F. oxysporum Fo47 appeared to be mainly ascribed to microbial antagonism but also to a lesser extent to systemic induced resistance. This induced resistance could be related to the accumulation of PR-1 and chitinases. The possible relationship between the ability of Fo47 to suppress fusarium wilt more efficiently than WCS417r and its ability to show both mechanisms is discussed.
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  • 33
    ISSN: 1573-8248
    Keywords: Bacillus thuringiensis var. tenebrionis ; biological control ; Coleoptera ; Chrysomelidae ; Coccinellidae ; Leptinotarsa decemlineata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Field studies to assess the impact of Bacillus thuringiensis var. tenebrionis (Btt)-insecticides on Colorado potato beetle populations, egg survivorship and levels of predation on egg masses were conducted in replicated field research plots during two years. Stage-specific abundance of the Colorado potato beetle and predation on egg masses were monitored in Btt-treated and untreated potato plots in both years. The Btt-treatments significantly reduced densities of large (third and fourth instar) Colorado potato beetle larvae. The densities of large larvae remained below 0.5 and 3 per plant in the Btt-treatment while peak densities of 4.5 and 21 large larvae per plant occurred in the untreated control in 1992 and 1993, respectively. Regular sampling of egg masses indicated that predation rates in Btt-treated and untreated plots did not differ significantly although, in 1993, predation rates of up to 100% were recorded, only in Btt-treated plots. In a predator exclusion study carried out in 1992, survivorship of protected eggs was consistently higher than of eggs exposed to predation. Seasonal survivorship of exposed eggs was significantly lower in the Btt-treated than in untreated plots. Btt insecticides for control of Colorado potato beetles provided direct protection of the crop and were compatible with naturally-occurring biological control of Colorado potato beetle eggs due to predation.
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  • 34
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    BioControl 43 (1998), S. 215-224 
    ISSN: 1573-8248
    Keywords: biological control ; host specificity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The frond-feeding weevil, Stenopelmus rufinasus Gyllenhal, was imported into quarantine for testing as a potential natural enemy for the invasive fern Azolla filiculoides Lamarck in South Africa. Adult S. rufinasus lived for approximately 55 days during which the females produced on average 325 offspring. The developmental period for the immature stages (egg, three larval instars and pupation) was about 20 days indicating the potential for several overlapping generations per year. Both the adults and the larvae caused severe damage to A. filiculoides in the laboratory. Host specificity of this insect was determined by adult no-choice oviposition and larval starvation tests on 31 plant species in 19 families. Adult feeding, oviposition and larval development was only recorded on the Azolla species tested (A. filiculoides, A. pinnata subsp. poss. asiatica R.K.M. Saunders and K. Fowler, A. pinnata subsp. africana (Desv.) R.K.M. Saunders and K. Fowler and A. nilotica De Caisne Ex Mett.). A. filiculoides proved to be significantly the most suitable host for the weevil. The low adult emergence from A. nilotica and A. pinnata subsp. africana would most probably prevent the weevil from establishing on them in the field. A. pinnata subsp. poss. asiatica which supported greater development, is thought to be introduced and has a weedy phenology in South Africa and is thus of low conservation value. Therefore, any damage inflicted on this plant in the field may be an acceptable trade-off for the predicted impact of S. rufinasus on the aggressive exotic weed, A. filiculoides.
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  • 35
    ISSN: 1573-8248
    Keywords: abnormal wings ; adult ; biological control ; Coccinellidae ; Coleoptera ; mutagenesis ; mutation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The use of coccinellids in the biological control of aphids is restricted to the release of larvae because adults tend to fly away. Non-flying adults may stay longer in one place and so they and their progeny could give longer term protection to plants. This work is an attempt to produce a non-flying population by the use of a chemical mutagen and selection of adults with wing malformations through their subsequent generations. These adults are characterized by open elytra and extended wings. Some general features of this mutation were disclosed. The mutation is either unexpressed or results in malformed wings. It also seems recessive and lethal when homozygous. The adults with the mutation suffered a high level of mortality and a drastic reduction in reproductive capacity that prevents their mass rearing for biological control. This study revealed a negative relationship between wing malformations and reproductive capacity. Nevertheless, when adults with the mutation were released in greenhouses containing cucumbers infested with the aphid Aphis gossypii, they remained on the plants in higher numbers and laid eggs over a longer period of time than the control adults but their progeny were less numerous.
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  • 36
    ISSN: 1573-8248
    Keywords: Aphelinidae ; biological control ; Diaspididae ; Encarsia citrina ; Encyrtidae ; Habrolepis aspidioti ; Homoptera ; Hymenoptera ; Marietta leopardina ; parasitism ; pest control ; spray oils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The black parlatoria, Parlatoria ziziphi, a common pest of citrus in the tropics and subtropics, has become the most important citrus pest in Upper Egypt. Spray oils may be a relatively safe alternative to harmful synthetic insecticides. However, the effect of spray oils on black parlatoria and associated parasitoids is unknown. Field studies were conducted in Giza, Egypt to assess the effect of two experimental spray oils on P. ziziphi and three associated parasitoid species on grapefruit (Citrus paradisi). Triona oil was more effective than Shecrona oil and reduced scale populations by up to 99% 75 days after application. The parasitoid Encarsia citrina was not affected significantly by either spray oil. Triona oil was slightly harmful to the other primary parasitoid, Habrolepis aspidioti and reduced parasitism rate by Marietta leopardina. However, because the latter species is a hyperparasitoid, the reduction in its number by Triona was beneficial. Triona application is therefore highly effective in controlling the black parlatoria and it reduced the rate of hyperparasitism by M. leopardina. The oils had only a minor negative impact and only on the less important primary parasitoid in the system.
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    BioControl 43 (1998), S. 87-95 
    ISSN: 1573-8248
    Keywords: biological control ; Diptera ; Entomophthoraceae ; infectivity ; insect pathogenic fungi ; Musca domestica ; Muscidae ; Zygomycetes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In this paper, the effect of age, humidity, and temperature on the conidial survival of Entomophthora muscae was evaluated. E. muscae was obtained from Musca domestica in a dairy in Itatiba (São Paulo, Brazil) and maintained in the laboratory by continuous passage through flies. Furthermore, the ability of conidia to infect flies at three temperatures (17, 21, and 27 °C), four ages of conidia (12, 72, 96, and 154 hours) and two humidities (100 and 60% RH) was evaluated. The temperature of 21 °C was the most favorable for the infection of house flies. Humidity was a cause of variation at 27 °C when the conidia were up to 12 hours old, but had no effect at lower temperatures. Conidia held at 100% RH and aged 72 hours caused no infection at 17 °C, but were infective at 21 °C. In the present study, conidia retained viability much longer than previously observed. Finally, the effect of humidity, temperature, and conidial age is discussed.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 29-48 
    ISSN: 0363-9061
    Keywords: hydraulic behaviour ; joint ; mechanics of joint ; joint degradation ; joint elements ; interface mechanics ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Constitutive laws for rock joints should be able to reproduce the fundamental mechanical behaviour of real joints, such as dilation under shear and strain softening due to surface asperity degradation. In this work, we extend the model of Plesha to include hydraulic behaviour. During shearing, the joint can experience dilation, leading to an initial increase in its permeability. Experiments have shown that the rate of increase of the permeability slows down as shearing proceeds, and, at later stages, the permeability could decrease again. The above behaviour is attributed to gouge production. The stress-strain relationship of the joint is formulated by appeal to classical theories of interface plasticity. It is shown that the parameters of the model can be estimated from the Barton-Bandis empirical coefficients; the Joint Roughness Coefficient (JRC) and the Joint Compresive strength (JSC). We further assume that gouge production is also related to the plastic work of the shear stresses, which enables the derivation of a relationship between the permeability of the joint and its mechanical aperture. The model is implemented in a finite element code (FRACON) developed by the authors for the simulation of the coupled thermal-hydraulic-mechanical behaviour of jointed rock masses. Typical laboratory experiments are simulated with the FRACON code in order to illustrate the trends predicted in the proposed model. © 1998 by John Wiley & Sons. Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 229-238 
    ISSN: 0363-9061
    Keywords: inclined shaft ; stress distribution ; field stress ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: In this study, the vertical overburden pressure in the vicinity of an inclined circular underground opening is defined by relation to the geometry of the medium. The stresses around the opening consisting of six components are induced by geostatic field stress. In this regard, the inclined circular opening i.e. shaft changes the original stress condition and an interrupted region develops beneath it. Three zones are defined on a plane which is perpendicular to the axis of shaft. The mathematical expressions of vertical overburden stresses at these three zones are established, respectively. The example given in appendix demonstrates the variation of radial and tangential stresses around the inclined shaft. It is seen that the stress distributions in the third zone, which includes the interrupted region, beneith the shaft display different configurations than that of those obtained by undisturbed field stresses. In the interrupted region the stresses around the shaft linearly grow up due to increasing overburden pressure by radial distance from the periphery of the shaft. At the boundary of interrupted region stresses jump to the original values induced by field stresses. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 197-227 
    ISSN: 0363-9061
    Keywords: elastoplasticity ; constitutive equation ; subloading surface model ; cyclic plasticity ; soil ; rotational hardening ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The subloading surface model fulfills the mechanical requirements for constitutive equations, i.e. the continuity condition, the smoothness condition and the work rate stiffness relaxation and describes pertinently the Masing effect. The constitutive equation of soils is formulated by introducing the subloading surface model and formulating the evolutional rule of rotational hardening for the description of anisotropy. The applicability of the constitutive equation to the prediction of real soil deformation behaviour is verified by predicting monotonic and cyclic loading behaviour of sands under drained and undrained conditions and comparing them with test data. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 303-322 
    ISSN: 0363-9061
    Keywords: pile driving ; open-ended piles ; plugging mechanism ; one-dimensional modelling ; stress wave propagation ; finite element analysis ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The plugging mechanism of infinitely-long open-ended piles is examined using numerical simulation of the wave propagation inside the soil plug and pile. It is shown that the key parameters for the plugging mechanism are the pile radius, the shape of the impact load, the shear wave velocity of the soil inside the pile, and the friction at the pile-soil interface. Consequently, the tendency of the pile to plug during driving can be assessed prior to the driving process by consideration of these key parameters. Existing one-dimensional models for the shaft response of open-ended piles are discussed and an improved model is presented. The differences between using one-dimensional models and finite element models to simulate the plugging process are examined. The differences are found to vary with the key parameters. Pile-in-pile and lumped-mass one-dimensional models are found to give satisfactory performance for some parameter combinations, while for others an axisymmetric finite element model must be used. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 425-447 
    ISSN: 0363-9061
    Keywords: closed-form solution ; transversely isotropic half-space ; Fourier transform ; Hankel transform ; rock anisotropy ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: We rederive and present the complete closed-form solutions of the displacements and stresses subjected to a point load in a transversely isotropic elastic half-space. The half-space is bounded by a horizontal surface, and the plane of transverse isotropy of the medium is parallel to the horizontal surface. The solutions are obtained by superposing the solutions of two infinite spaces, one acting a point load in its interior and the other being free loading. The Fourier and Hankel transforms in a cylindrical co-ordinate system are employed for deriving the analytical solutions. These solutions are identical with the Mindlin and Boussinesq solutions if the half-space is homogeneous, linear elastic, and isotropic. Also, the Lekhnitskii solution for a transversely isotropic half-space subjected to a vertical point load on its horizontal surface is one of these solutions. Furthermore, an illustrative example is given to show the effect of degree of rock anisotropy on the vertical surface displacement and vertical stress that are induced by a single vertical concentrated force acting on the surface. The results indicate that the displacement and stress accounted for rock anisotropy are quite different for the displacement and stress calculated from isotropic solutions. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 575-595 
    ISSN: 0363-9061
    Keywords: contaminant transport ; variable density flow ; fractures ; leakage ; dispersion ; diffusion ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A numerical model for simulating flow and transport of contaminants with variable density in fractured porous media is presented. The non-linearities arising from the density variation and the velocty-dependent dispersion terms have been handled by Picard method. It is shown that the contaminant transport in a fractured porous medium is initially dominated by fractures. However, with time increasing, the contaminant concentration in porous blocks increases, due to the leakage of contaminant from the fracture network to the porous blocks. It is also shown that the high density of contaminant has a greater effect on its transport in the fracture network than in the porous blocks. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 671-687 
    ISSN: 0363-9061
    Keywords: recurrent neural network ; residual soil ; shear behaviour ; simulation ; prediction ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Modelling of shear behaviour of residual soils is difficult in that there is a significant variability in constituents and structures of the soil. A Recurrent Neural Network (RNN) is developed for modelling shear behaviour of the residual soil. The RNN model appears very effective in modelling complex soil shear behaviour, due to its feedback connections from an hidden layer to an input layer. Two architectures of the RNN model are designed for training different sets of experimental data which include strain-controlled undrained tests and stress-controlled drained tests performed on a residual Hawaiian volcanic soil. A dynamic gradient descent learning algorithm is used to train the network. By training only part of the experimental data the network establishes neural connections between stress and strain relations. Although the soil exhibited significant variations in terms of shearing behaviour, the RNN model displays a strong capability in capturing these variabilities. Both softening and hardening characteristics of the soil are well represented by the RNN model. Isotropic and anisotropic consolidation conditions are precisely reflected by the RNN model. In undrained tests, pore water pressure responses at various loading stages are simultaneously simulated. With a RNN model designed for a special drained test, the network is able to capture abrupt changes in axial and volumetric strains during shearing courses. These good agreements between the measured data and the modelling results demonstrate the desired capability of the RNN model in representing a soil behaviour. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 749-769 
    ISSN: 0363-9061
    Keywords: wellbore stability ; sand erosion ; sand production ; sand prediction ; radial flow ; poroelasticity ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper extends earlier work on sand erosion and presents an attempt to couple sand erosion to mechanical damage of rock around a wellbore. Porosity which evolves in time and space as surface erosion progresses, is chosen as the coupling parameter. Both rock elasticity and strength (cohesion) are assumed to depend on porosity in such a way that the material becomes weaker with increasing porosity. The mathematical model, consists of erosion equations, mixture flow equations and stress equilibrium equations, is solved numerically by Galerkin finite element method. Numerical results suggest that erosion, resulting in sand production, is high close to the free surface. Erosion is accompained by changes in porosity and a significant permeability increase. Erosion in the vicinity of the wellbore induces alterations in the mechanical behaviour of the medium. Weakening of rock stiffness leads to severe alteration of both effective stresses and pore pressure near the cavity. Since cohesion decreases with increasing porosity, one can also identify the time instant at which rock mechanical failure starts. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 867-901 
    ISSN: 0363-9061
    Keywords: finite elements ; hydromechanical coupling ; fractured rock masses ; viscoplasticity ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This work presents a finite element implementation to treat the Hydromechanical Coupling (HM) in fractured rock masses under the framework of the so-called ‘equivalent continuum’ approach. The multilaminar concept, introduced by Zienkiewicz and Pande, is used to simulate the mechanical behaviour of both the intact rock and the families of fractures. In that concept, the non-linearities in the constitutive relations are dealt by means of fictitious viscoplasticity. In the present implementation, the mechanical behaviour of the fractures is modelled by means of Barton-Bandis model. The shear stress/shear displacement/dilatancy relationship is modelled as viscoplastic and the normal stress/normal displacement as non-linear viscoelastic. Flow along fractures is considered to occur as a sequence of permanent states. The permeability tensor of the equivalent continuum is determined from the hydraulic apertures, in accordance of Barton et al. From the numerical point of view, the basic aim of the work is the implementation of an efficient scheme to solve the above described problem. This is done by designing a self-adaptive time step control, transparent to the user, which determines the highest possible time step while assuming the conditions of precision, stability and convergence. The paper presents the numerical details of such scheme together with validation/comparative examples and the results obtained on the analysis of the fractured rock foundation of a hypothetical dam. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 1021-1033 
    ISSN: 0363-9061
    Keywords: retaining wall ; interface ; finite element ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A series of finite element analyses have been undertaken to investigate the effects of interface properties on the behaviour of a vertical retaining wall and the deformation of the ground around it. The boundary between a rigid embedded wall and the soil is modelled with zero thickness interface elements. Uniform translation of the wall has been studied. The analyses show the predicted limiting active and passive pressure on the wall are dependent on the maximum wall friction angle and are in reasonable agreement with accepted approximate analytical solutions. The limiting pressure is independent of the stiffness and dilation properties of the interface elements. The dilation properties of the interface have a significant effect on the ground surface deformation around the wall. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 1-27 
    ISSN: 0363-9061
    Keywords: expansive clay ; hydromechanics ; unsaturated soils ; nuclear waste ; in situ test ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: BACCHUS2 in situ isothermal wetting experiment has been analysed by means of a coupled flow-deformation approach. Backfill material, a mixture of Boom clay powder and high density pellets, has been extensively tested in the laboratory in order to determine its hydraulic and mechanical properties. Parameters of constitutive equations were derived from this experimental data base. Two mechanical constitutive models have been used in the simulation of the ‘in situ’ experiment: a state surface approach and an elastoplastic model. Calculations have shown several features of the hydration process which help to understand the behaviour of expansive clay barriers. Predictions using both models have been compared with each other and with actual measurement records. This has allowed a discussion of the comparative mertis of both approaches and the identification of some critical parameters of backfill behaviour. Overall agreement between calculations and field measurements is encouraging and shows the potential of the methods developed to model the behaviour of engineered clay barriers in the context of nuclear waste disposal. © 1998 by John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 75-95 
    ISSN: 0363-9061
    Keywords: three-dimensional ; heat ; moisture ; air ; transfer ; unsaturated ; soil ; Engineering ; Civil and Mechanical Engineering
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    Notes: A new three-dimensional numerical model of coupled heat, moisture and air transfer in unsaturated soil is presented. In particular, the model accommodates moisture transfer in the form of liquid and vapour flow and heat transfer arising from conduction, convection and latent heat of vaporization. The bulk flow of dry air and the movement of air in a dissolved state are also included. The theoretical basis of the model, the finite element solution of the spatial terms and finite difference solution of the temporal terms are briefly presented. Attention is focused on the verification of the new numerical solution. This is achieved via comparisons with independent solutions of heat, moisture and air transfer in an unsaturated soil. The physical problem considered includes the highly non-linear hydraulic properties of sand. Thermal conductivity is also included as a function of soil moisture content. Excellent correlation of results is shown thus providing confidence in the new model.The new model is also applied to a number of test cases which illustrate the need for the development of a model which can fully include three-dimensional behaviour. In particular, three applications are presented each increasing in complexity. The first application illustrates three-dimensional heat transfer. This particular application is verified against existing commercial finite element software. Subsequent applications serve to illustrate how the coupled processes of heat moisture and air transfer combine to yield three-dimensional problems even within a simple geometric domain. Visualization of three-dimensional results is also addressed. © 1998 by John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 175-196 
    ISSN: 0363-9061
    Keywords: shear crack ; singular integral equation ; excavation ; discontinuities ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The problem of the equilibrium of a plane with a circular hole and a shear crack is considered to model failure of an excavation (borehole or circular opening) in rocks weakened by discontinuities (planes of weakness). It is assumed that sliding occurs in a part of the plane of weakness when the Mohr-Coulomb friction criterion is satisfied due to the stress redistribution caused by the excavation. The method of singular integral equations is employed to solve the boundary value problem. Geomechanical problems concerning borehole breakout and rockburst caused by fault-opening interaction are discussed. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 277-301 
    ISSN: 0363-9061
    Keywords: seepage ; flow rate ; drain ; tunnel ; optimization ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The known formulae of Freeze and Cherry, Polubarinova-Kochina, Vedernikov for flow rate during 2-D seepage into horizontal drains and axisymmetric flow into cavities are examined and generalized. The case of an empty drain under ponded soil surface is studied and existence of drain depth providing minimal seepage rate is presented. The depth is found exhibiting maximal difference in rate between a filled and an empty drain. 3-D flow to an empty semi-spherical cavity on an impervious bottom is analysed and the difference in rate as compared with a completely filled cavity is established. Rate values for slot drains in a two-layer aquifer are ‘inverted’ using the Schulgasser theorem from the Polubarinova-Kochina expressions for corresponding flow rates under a dam. Flow to a point sink modelling a semi-circular drain in a layered aquifer is treated by the Fourier transform method. For unsaturated flow the catchment area of a single drain is established in terms of the quasi-linear model assuming the isobaric boundary condition along the drain contour. Optimal shape design problems for irrigation cavities are addressed in the class of arbitrary contours with seepage rate as a criterion and cavity cross-sectional area as an isoperimetric restriction. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 351-391 
    ISSN: 0363-9061
    Keywords: cone penetration testing ; sand ; Engineering ; Civil and Mechanical Engineering
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    Notes: The cone penetration test (CPT) is widely used, and although initially developed as a stratigraphic logging tool its excellent repeatability and accuracy offers a benchmark quantitative test for sand in particular. A continuing difficulty, however, is that the CPT does not measure any soil property directly, so that parameters of interest must be recovered from solution of an inverse boundary value problem, which is difficult. To date most CPT interpretations in sand have been based on very limited calibration testing carried out in large chambers on a few sands from which mappings are developed. But there are differences in the CPT response from one sand to another leaving the interpretation imprecise (and arguably even speculative) because these differences remain poorly understood. In this paper we use the familiar spherical cavity expansion analogy to the CPT including large strains and a good, critical-state-based, soil model to develop a pattern of behaviour which we then compare to some of the reference chamber test data. We find that one of the issues of dispute in the empirical interpretation methods, the so-called stress-level effect, is caused by neglect of elasticity and that there are several additional parameters of first-order significance to cavity expansion in sands. More generally, we show that the difference in CPT response between various chamber sands in predicted. Our results are cast in dimensionless form and the inversion illustrates that extreme care is required in interpreting CPT data if the in situ sand state is to be determined with precision approaching that suggested as achievable by the repeatability of the CPT data itself. Aspects requiring particular care in interpreting CPT data in sand are discussed. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 449-475 
    ISSN: 0363-9061
    Keywords: consolidation ; heat transfer ; poroelasticity ; pore pressure ; coupled fields ; Laplace transform ; Engineering ; Civil and Mechanical Engineering
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper presents a theoretical approach to analyse coupled, linear thermoporoelastic fields in a saturated porous medium under radial and spherical symmetry. The governing equations account for compressibility and thermal expansion of constituents, heat sink due to thermal dilatation of water and thermal expansion of the medium, and thermodynamically coupled heat-water flow. It has been reported in the literature that thermodynamically coupled heat-water flows known as thermo-osmosis and thermal filtration have the potential to significantly alter the flow fields in clay-rich barriers in the near field of a underground waste containment scheme. This study presents a mathematical model and examines the effects of thermo-osmosis and thermal-filtration on coupled consolidation fields in a porous medium with a cavity. Analytical solutions of the governing equations are presented in the Laplace transform space. A numerical inversion scheme is used to obtain the time-domain solutions for a cylindrical cavity in a homogeneous or a non-homogeneous medium. A closed form time-domain solution is presented for a spherical cavity in a homogeneous medium. Selected numerical solutions for homogeneous and non-homogeneous media show a significant increase in pore pressure and displacements due to the presence of thermodynamically coupled flows and a negligible influence on temperature. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 421-423 
    ISSN: 0363-9061
    Keywords: Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 603-619 
    ISSN: 0363-9061
    Keywords: earthquakes ; stress-strain response ; downhole arrays ; Engineering ; Civil and Mechanical Engineering
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Recordings from downhole accelerometer arrays offer unique insight into soil behavior and ground response during earthquakes. In this paper we present a scheme for interpolating displacement and acceleration measurements to provide approximations for subsurface shear strain and stress as continuous functions of time. Our suggested interpolating functions are constructed in such a way that the free surface boundary condition will always be satisfied and the interpolated displacement and acceleration remain finite for all depths. We also show how the functions can be adapted to represent layered soil profiles. Depending on the number of instruments in the downhole array, a truncated series of functions can be derived so that each represents a modal shape for the layered soil profile. The resulting approximations for strain and stress are considered more accurate and robust than previous approximations. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 621-653 
    ISSN: 0363-9061
    Keywords: state parameter ; stress-state relation ; constitutive modelling ; plasticity ; critical state ; sand and clay ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The purpose of this paper is to present a simple, unified critical state constitutive model for both clay and sand. The model, called CASM (Clay And Sand Model), is formulated in terms of the state parameter that is defined as the vertical distance between current state (v, p′) and the critical state line in v-ln p′ space. The paper first shows that the standard Cam-clay models (i.e. the original and modified Cam-clay models) can be reformulated in terms of the state parameter. Although the standard Cam-clay models prove to be successful in modelling normally consolidated clays, it is well known that they cannot predict many important features of the behavior of sands and overconsolidated clays. By adopting a general stress ratio-state parameter relation to describe the state boundary surface of soils, it is shown that a simple, unified constitutive model (CASM) can be developed for both clay and sand. It is also demonstrated that the standard Cam-clay yield surfaces can be either recovered or approximated as special cases of the yield locus assumed in CASM.The main feature of the proposed model is that a single set of yield and plastic potential functions has been used to model the behaviour of clay and sand under both drained and undrained loading conditions. In addition, it is shown that the behaviour of overconsolidated clays can also be satisfactorily modelled. Simplicity is a major advantage of the present state parameter model, as only two new material constants need to be introduced when compared with the standard Cam-clay models. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 855-865 
    ISSN: 0363-9061
    Keywords: anchor ; trapdoor ; limit load ; cohesionless ; associative ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A methodology for determining the plane strain limit load acting on an anchor or trapdoor buried within a purely associative Coulomb soil is presented. True lower bounds derived from a family of limiting stress fields appropriate to shallow horizontal trapdoors and anchors are shown to correlate to within less than 1 percent of upper bounds available in the literature, permitting the true limit load to be almost exactly defined. The solution form alters for deeply buried anchors and trapdoors resulting in poorer correlations. Methods by which the work may be extended to cover the more practical instances of non-associative Coulomb soils are indicated but are beyond the scope of the current paper. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 903-919 
    ISSN: 0363-9061
    Keywords: hollow cylinders ; diffuse mode bifurcations ; geomaterials ; non-normality ; pressure-sensitivity ; Engineering ; Civil and Mechanical Engineering
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    Notes: This paper derives analytically the condition for the onset of diffuse mode bifurcations in thick-walled hollow cylinders with internal radius a, external radius b and length L under axial compression and confining pressure. The thick-walled cylindrical specimens are made of geomaterial characterized by Rudnicki's constitutive model, and the method of solution for the governing equations is the velocity potential approach employed by Chau. Numerical results show that thick-walled cylinders are stronger than thin-walled cylinders against diffuse mode bifurcations, including both buckling, axisymmetric and non-axisymmetric deformations. In contrast to the conclusion for solid cylinders (Chau), no buckling solution is found for γ = mπa / L smaller than about 0·7 under compression for a fixed and finite value of a / b (i.e. no buckling for long and slender hollow cylinders with small a / L and fixed b / a). When 0·7 〈 γ 〈 0·9, buckling is the expected first bifurcation; whereas, when γ 〉 0·9, bulging or barrelling is anticipated. The exact value of γ that excludes buckling and separates the buckling and barrelling phenomena depends on the current values of the constitutive parameters of the solid. Hollow cylinders with higher degree of anisotropy, disobeying normality flow rule, and subjected to confining pressure are more conducive to bifurcations than cylinders made of materials with isotropy, obeying normality, and subjected to no confining pressure. In addition, diffuse mode bifurcations are found possible in the pre-peak regime of the stress-strain curve. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 983-1000 
    ISSN: 0363-9061
    Keywords: geomechanics ; indirect boundary element method (BEM) ; three-dimensional (3-D) elastostatics ; iterative methods ; approximate solution ; Engineering ; Civil and Mechanical Engineering
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The research herein primarily addresses to geomechanical problems of underground constructions in Mining and Civil Engineering. The problems are solved using the Indirect Boundary Element Method (IBEM). Although the geometry of the constructions themselves is usually very complicated, it will become much more complicated if we were to draw the existing joints. The computational problem therefore is how to deal with huge amount of equations and find out efficient methods of their formation and solution keeping in mind restraints of the computer memory and calculation time. Several approaches are used to enhance the performance of the Indirect Boundary Element Method. One of them deals with application of efficient equation solvers. It is shown that Krylov-type methods like CGS and GMRES with simple Jacoby preconditioning appear to be efficient and robust. In addition, adaptive integration on the boundary elements, together with diagonal dominance of equationsmake it possible to accelerate convergence of the iterative procedure. Some of the problems discussed allow a substantial reduction of matrix entries that leads to a very cheap iterative solution keeping reasonable accuracy of the results. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 97-132 
    ISSN: 0363-9061
    Keywords: constitutive model ; rate-independent type ; strain response envelope ; granular material ; uniqueness ; Engineering ; Civil and Mechanical Engineering
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper reviews some incrementally non-linear constitutive equations of interpolation type, and proposes a new approach to illustrate the discrepancies between different interpolation models. This approach uses the strain response envelopes, based on experimental data when restricted to triaxial plane, and the Jacobian of the constitutive equations to examine the loss of uniqueness. A new family of interpolation functions is proposed to meet the three requirements: C1-continuity of strain response envelope, correct description of experimental data, and respect of the one-to-one property. © 1998 by John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 153-174 
    ISSN: 0363-9061
    Keywords: finite-element ; sea ice pack ; rheology ; viscous-plastic ; viscous fluid ; Engineering ; Civil and Mechanical Engineering
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    Notes: In this paper the effects of four different rheologies on the evolution of a large-scale sea ice pack are determined and compared. Two rheologies are of viscous-plastic form, and two are viscous fluid relations. The initial pack domain is rectangular, and the motion is driven by wind stress and resisted by ocean drag. Two adjacent edges are rigid shore boundaries, and the other two are free boundaries at open water which move during the pack motion, so that the pack domain changes in time. Two different forms of boundary conditions at the rigid shore edges are considered, which also influence the evolution. The governing equations are solved numerically using a finite-element method, and, unlike previous numerical treatments, no artificial viscosity is incorporated to stabilise the algorithm near interfaces between converging and diverging flow. Instability arises when any tensile stress is abruptly cut-off when diverging flow is initiated, and an alternative view is offered. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 263-275 
    ISSN: 0363-9061
    Keywords: non-ideal interface ; crack scattering ; domain decomposition ; collocation methods ; Engineering ; Civil and Mechanical Engineering
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    Notes: This work presents a numerical algorithm for solving crack scattering in a transversely isotropic medium whose symmetry axis is perpendicular to the crack surface. The crack is modelled as boundary discontinuities in the displacement u and the particle velocity v, of the stresses [κu+ζv], where the brackets denote discontinuities across the interface. The specific stiffness κ introduces frequency-dependence and phase changes in the interface response and the specific viscosity ζ is related to the energy loss.The numerical method is based on a domain decomposition technique that assignes a different mesh to each side of the interface, that includes the crack plane. As stated above, the effects of the crack on wave propagation are modelled through the boundary conditions, that require a special boundary treatment based on characteristic variables. The algorithm solves the particle velocity-stress wave equations and two additional first-order differential equations (two-dimensional case) in the displacement discontinuity. For each mesh, the spatial derivatives normal to the interface are solved by the Chebyshev method, and the spatial derivatives parallel to the interface are computed with the Fourier method. They allow a highly accurate implementation of the boundary conditions and computation of the spatial derivatives, and an optimal discretization of the model space. Moreover, the algorithm allows general material variability. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 327-350 
    ISSN: 0363-9061
    Keywords: finite element analysis ; large strain ; remeshing ; integration ; penetration ; bearing capacity ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A practical method is presented for numerical analysis of problems in solid (in particular soil) mechanics which involve large strains or deformations. The method is similar to what is referred to as ‘arbitrary Lagrangian-Eulerian’, with simple infinitesimal strain incremental analysis combined with regular updating of co-ordinates, remeshing of the domain and interpolation of material and stress parameters. The technique thus differs from the Lagrangian or Eulerian methods more commonly used. Remeshing is accomplished using a fully automatic remeshing technique based on normal offsetting, Delaunay triangulation and Laplacian smoothing. This technique is efficient and robust. It ensures good quality shape and distribution of elements for boundary regions of irregular shape, and is very quick computationally. With remeshing and interpolation, small fluctuations appeared initially in the load-deformation results. In order to minimize these, different increment sizes and remeshing frequencies were explored. Also, various planar linear interpolation techniques were compared, and the unique element method found to work best.Application of the technique is focused on the widespread problem of penetration of surface foundations into soft soil, including deep penetration of foundations where soil flows back over the upper surface of the foundation. Numerical results are presented for a plane strain footing and an axisymmetric jack-up (spudcan) foundation, penetrating deeply into soil which has been modelled as a simple Tresca or Von Mises material, but allowing for increase of the soil strength with depth. The computed results are compared with plasticity solutions for bearing capacity. The numerical method is shown to work extremely well, with potential application to a wide range of soil-structure interaction problems. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 495-508 
    ISSN: 0363-9061
    Keywords: consolidation ; cohesive soil ; clay ; axial strain ; true triaxial ; finite difference method ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper presents a simplified approach for the analysis of axial strain induced by three-dimensional consolidation of cohesive soils. The axial strain is divided into a constant volume component and a consolidation component. A relevant undrained stress-strain relationship is required to determine the constant volume component. A theoretical formulation is developed for the evaluation of the consolidation component. Predictions of the axial strain accompanying true triaxial laboratory tests for a variety of stress patterns correlate sufficiently well with the measured data. The proposed method is potentially applicable in conjunction with a finite difference scheme to analyze the time-dependent response of pile groups subjected to static vertical loading. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 549-574 
    ISSN: 0363-9061
    Keywords: carbonatic clays ; thermo-plasticity ; nuclear waste disposal ; thermo-mechanical tests ; Engineering ; Civil and Mechanical Engineering
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    Notes: Argillaceous masses considered for potential nuclear waste repositories may exhibit significant space variability in their carbonate content. This may affect mechanical clay properties, such as strength or maximum apparent preconsolidation stress known to strongly depend on carbonate content. This paper investigates experimentally the dependence of thermo-hydro-mechanical behaviour of clays on carbonate content. The properties investigated are thermal strains, thermally induced over-consolidation, strength changes, destructuration, and thermally developed water pressure in undrained conditions. The experimental data are analysed in terms of a thermo-elasto-plasticity theory for clays, being an extension of Cam-clay model, modified to include the variability of the carbonatic content. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 695-720 
    ISSN: 0363-9061
    Keywords: wave propagation ; compaction ; pore pressure generation ; Engineering ; Civil and Mechanical Engineering
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    Notes: The propagation of a plane load-unload pulse through a compacting sand is analysed and illustrated for both dry sand and liquid saturated sand in undrained conditions. A major feature is the interaction between the initial loading wave and the faster following unloading wave. Free draining and undrained conditions exhibit distinct qualitative and quantitative results, and the pore liquid pressure generation is a significant physical feature. Illustrations show the effects of different applied surface pulse shapes. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 777-790 
    ISSN: 0363-9061
    Keywords: piles ; rafts ; finite elements ; preconditioning ; conjugate gradients ; Engineering ; Civil and Mechanical Engineering
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Analysis of piled raft foundations, taking account of their full three-dimensional complexity, can be accomplished by modern finite element analysis techniques. The characteristics of the (preconditioned conjugate gradient) numerical method applied to this problem are analysed, and then the method isused in a field problem of a raft subjected to very rapidly varying loading patterns. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 791-818 
    ISSN: 0363-9061
    Keywords: Engineering ; Civil and Mechanical Engineering
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    Notes: An analytical model to simulate the penetration of the piezocone penetrometer in cohesive soils is presented here. The elasto-plastic coupled field equations of the saturated cohesive soils (given by Voyiadjis and Abu-Farsakh) is used in this analysis. The numerical simulation of the piezocone penetration is implemented into a finite element program. The analytical model is used to analyze the miniature piezocone penetration tests (PCPT) conducted at LSU calibration chambers. Simulation of the piezocone penetration is done for two cases. In the first case, the soil-penetrometer interface friction is neglected, while in the second case, the soil-penetrometer interface friction is taken into consideration. The constraint approach is used to model the soil-piezocone interface friction in which the Mohr-Coulomb frictional model is used to define the sliding potential. Analysis is done for three different soil specimens with different stress histories. The results of the numerical simulations are compared with the experimental measurements of the miniature piezocone penetration tests (PCPT) in cohesive soil specimens conducted in LSU calibration chambers. The resulting excess pore pressure distribution and its dissipation using the numerical model are compared with some available prediction methods. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 1001-1020 
    ISSN: 0363-9061
    Keywords: stone-column reinforcement ; homogenisation technique ; elastoplastic analysis ; sub-iteration scheme ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A numerical model is proposed to analyse elastic as well as elastoplastic behaviour of stone-column reinforced foundations. The stone-columns are assumed to be dispersed within the in situ soil and a homogenization technique is invoked to establish equivalent material properties for in situ soil and stone-column composite. The difficulties encountered in carrying out elastoplastic analyses of composite materials are overcome by adopting a separate yield function for each of the constituent materials and a sub-iteration procedure within an implicit backward Euler stress integration scheme. In the proposed procedure, equilibrium as well as kinematic conditions implied in the homogenization procedure are satisfied for both elastic as well as elastoplastic stress states.The proposed model is implemented in an axi-symmetric finite element code and numerical prediction is made for the behaviour of model circular footings resting on stone-column reinforced foundations. This prediction indicates good agreement with experimental observation. Finally, a new scheme in which the length of stone-column is variable is proposed and its behaviour is examined through a numerical example. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 969-981 
    ISSN: 0363-9061
    Keywords: heat and moisture flow ; analytical solution ; transient analysis ; spherical heat source ; coupled analysis ; Green's function method ; Engineering ; Civil and Mechanical Engineering
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The present paper develops an analytical approach to the problem of heat-induced moisture movement in the vicinity of a spherical heat source embedded in an undeformable, moist porous solid of infinite extent. A transient-state distribution of temperature within the infinite medium is assumed to induce the moisture transport process. The numerical results, presented in the paper, illustrate the influence of the moisture transport characteristics on the time-dependent distribution of moisture within the porous medium. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 49-71 
    ISSN: 0363-9061
    Keywords: unsaturated soil ; heat transfer ; moisture transfer and stress-strain behaviour ; model and validation ; Engineering ; Civil and Mechanical Engineering
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper focuses attention on the development of a numerical model of the hydro/thermo/mechanical behaviour of unsaturated clay and its consequent verification and validation. The work presented describes on-going collaboration between the Cardiff School of Engineering and Atomic Energy of Canada. The model development, which was carried out at Cardiff, can be described as being based on a mechanistic approach to coupled heat, moisture and air flow. This is then linked to a deformation analysis of the material within a ‘consolidation’ type of model. The whole is solved via the finite element method to yield a computer software code named COMPASS (COde for Modelling PArtly Saturated Soil). Some aspects of verification and validation of the model have been addressed in-house. However, the purpose of current AECL work is to provide an independent, rigorous, structured programme of validation and the paper will also explore the further validation of COMPASS within this context. © 1998 by John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 133-149 
    ISSN: 0363-9061
    Keywords: thermoporoelasticity ; thermoporoplasticity ; Laplace transform ; Stehfest algorithm ; finite element method ; Engineering ; Civil and Mechanical Engineering
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Solutions are presented for the behaviour of a layered porous space which contains a decaying heat source. Such a problem arises when high-level nuclear waste is placed in deep underground depositories in deep clayey formations of sedimentary basins. The geometry of the problem is one dimensional and the porous space is constituted by two layers: a deep low permeability layer which contains the nuclear waste disposal and a superficial layer. The solution is used to examine the effects of contrasts of permeability, thermal conductivity and specific heat capacities between the two layers on the large-scale behaviour of the porous space. Results are presented, using realistic data, for the pore pressure and temperature evolution at the heat source centre, and for the vertical displacement of the ground level. The superficial layer has no significant effects on pore pressure, temperature and stress evolution near the heat source centre. The vertical displacement of the ground level is mainly due to the thermal dilatation of the pore water, so it decreases with an increasing of permeability of the superficial layer. The solution of the time-dependent problem is carried out by applying Laplace transforms to the field variables, obtaining solutions and then using numerical methods to invert the transformed solutions. Comparisons with numerical simulations taking into account the non-linear and non-reversible behaviour of the rock mass are presented. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 245-261 
    ISSN: 0363-9061
    Keywords: Cosserat continuum model ; equivalent continuum medium ; layered rock mass ; finite element method ; non-associative plasticity ; Engineering ; Civil and Mechanical Engineering
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Layered rock masses can be modelled either as standard, orthotropic continua if the layer bending can be neglected or as Cosserat continua if the influence of layer bending is essential. This paper presents a finite element smeared joint model based on the Cosserat theory. The layers are assumed to be elastic with equal thickness and equal mechanical properties. All the cosserat parameters are expressed through the elastic properties of layers, layer thickness and joint stiffness. Plastic-slip as well as tensile-opening of layer interface (joint) are accounted for in a manner similar to the conventional non-associative plasticity theory.As an application, the behaviour of an excavation in a layered rock mass is examined. The displacement and stress fields given by smeared joint models based on the Cosserat continuum and the conventional anisotropic continuum approaches are compared with those obtained from the discrete joint model. The conventional anisotropic continuum model is found to break-down completely when the effective shear modulus in the direction parallel to layering is low in comparison to the shear modulus of the intact layer, whereas the Cosserat model is found to be capable of accurately reproducing complex load-deflection patterns irrespective of the differences in shear moduli. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 393-416 
    ISSN: 0363-9061
    Keywords: fabric ; porosity ; tensor ; yield ; stress ; strain ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The porosity of soils is considered to be a directional measure and its distribution is characterized by a functional form. This form has been used to extend the critical state soil mechanics framework to include the effects of structure in soils. A new internal plastic energy dissipation formulation has been proposed to account for fabric arrangement. New expressions for the yield locus, and the plastic stress-strain response of structural soils have been derived. The applicability of the concepts to model the plastic stress-strain behaviour of a number of soils is illustrated. The advantage of the new model is very well identified in modelling the stress-strain behaviour of K0 consolidated and natural clays. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 477-493 
    ISSN: 0363-9061
    Keywords: foundation ; pile ; raft ; analysis ; case history ; Engineering ; Civil and Mechanical Engineering
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    Notes: An approximate numerical method for the analysis of piled raft foundations is presented. The raft is modelled as a thin plate and the piles as interacting non-linear springs. Both the raft and the piles are interacting with the soil which is modelled as an elastic layer. Two sources of non-linearity are accounted for: (i) the unilateral contact at the raft-soil interface and (ii) the non-linear load-settlement relationship of the piles. Both theoretical solutions and experimental results are used to verify that, despite the approximations involved, the proposed method of analysis can provide satisfactory solutions in both linear and non-linear range. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 515-548 
    ISSN: 0363-9061
    Keywords: coupled analysis ; expansive clay ; granite ; radioactive waste ; thermo-hydro-mechanical analysis ; unsaturated soils ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Coupled thermo-hydro-mechanical (THM) analyses have been used to examine the interacting phenomena associated with the simultaneous heating and hydration of an engineered bentonite barrier placed in a drift excavated in granite. The specific problem studied is an in situ test being carried out in the underground laboratory at Grimsel (Switzerland). After describing the test and the theoretical formulation, the results of a coupled THM analysis using the best parameter estimation currently available are presented and discussed. The effect of various features of analysis are explored by means of additional analyses in which each of those features are varied, one at the time. Finally, sensitivity analyses have been carried out to examine some critical aspects of the in situ test design. Performance of coupled THM analyses has led to a better understanding of the various inter-related phenomena occurring during heating and hydration of the engineered clay barrier. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 655-669 
    ISSN: 0363-9061
    Keywords: elastic nonhomogeneity ; soil deformation ; soil stresses ; surface loading ; Engineering ; Civil and Mechanical Engineering
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    Notes: The response of a compressible continuously non-homogeneous elastic soil to a static vertical point load on its surface is analytically investigated by using classical integral transform techniques and the extended power series method for obtaining the solution in the transform domain. The non-homogeneity is described by means of a depth-function which is non-zero at the surface and bounded at infinity and is capable in modelling both increasing and decreasing soil stiffness with depth. The influence of non-homogeneity on the displacements and stresses at the surface and in the interior is examined over a wide range on the governing parameters. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 721-748 
    ISSN: 0363-9061
    Keywords: cyclic behaviour ; saturated sands ; disturbed state concept ; liquefaction ; post liquefaction ; threshold transitions ; laboratory tests ; validations ; mathematical analysis ; computer implementation ; application ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A fundamental procedure is proposed for the identification of liquefaction in saturated soils based on the instability in the material's microstructure. The disturbed state concept (DSC) provides a unified constitutive model for the characterization of entire stress-strain behaviour under cyclic loading, and the values of disturbance at threshold states in the deforming microstructure provides the basis for the identification of liquefaction. The procedure is verified with respect to laboratory behaviour of two sands, saturated Ottawa and Reid Bedford. A mathematical analysis of the DSC constitutive matrix is also performed. Procedures for the application of the DSC for simplified analysis and design, and in finite element procedures are presented. It is believed that the proposed model can provide a fundamental yet simplified procedure for liquefaction analysis, and as a result, it is considered to be an improvement over the available empirical and energy-based procedures. © 1998 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 819-850 
    ISSN: 0363-9061
    Keywords: stochastic ; finite element ; seismic ; response ; random ; variability ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Some of the available stochastic finite element methods are adapted and evaluated for the analyses of response of soils with uncertain properties subjected to earthquake induced random ground motion. In this study, the dynamic response of a soil mass, with finite element discretization, is formulated in the frequency domain. The spectral density function of the response variables are obtained from which the evaluation of the root-mean-squared and the most probable extreme values of the response are made. The material non-linearities are incorporated by using strain compatible moduli and damping of soils using an equivalent linear model for stress-strain behaviour of soils and an iterative solution of the response. The spatial variability of the shear modulus is described through a random field model and the earthquake included motion is treated as a stochastic process. The available formulations of direct Monte-Carlo simulation, first-order perturbation method, a spectral decomposition method with Neumann expansion and a spectral decomposition method with Polynomial Chaos are used to develop stochastic finite element analyses of the seismic response of soils. The numerical results from these approaches are compared with respect to their accuracy and computational efficiency. © 1998 John Wiley & Sons Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 921-940 
    ISSN: 0363-9061
    Keywords: anisotropic sand ; constitutive model ; non-linear tensorial junctions ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The paper presents a constitutive model for the three-dimensional deformation-strength behaviour of inherently anisotropic sand. Based on non-linear tensorial functions, the model is developed without recourse to the concepts in plasticity theory such as yield surface and plastic potential. Benefited from the fact that no decomposition of strain into elastic and plastic parts is assumed, a unified treatment of anisotropic behaviour of deformation and strength is achieved. Anisotropy is characterized by a vector normal to the bedding plane. The extension of the constitutive model is furnished by incorporating the vector under consideration of the principle of objectivity and the condition of material symmetry. Distinct features of the model are its elegant formulation and its simple structure involving few material parameters. Model performance and comparison with experiments show that the model is capable of capturing the salient behaviour of anisotropic sand. © 1998 John Wiley & Sons, Ltd.
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  • 81
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    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 947-968 
    ISSN: 0363-9061
    Keywords: boundary element method ; complex hypersingular integrals ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The definitions of complex integrals of Cauchy and Hadamard with the singular point coinciding with the end point of the integration curve are proposed. It is shown that the new integrals satisfy most of the properties of the regular ones, including the change of variables. It is also shown that the Cauchy principal value (CPV) and Hadamard finite-part (HFP) integrals can be considered as a sum of the new type integrals. The application to numerical solution by the boundary element method (BEM) and the complex hypersingular integral equation (CHSIE) for the multiregions of interacting elastic bodies and bodies with cracks and holes is discussed. The different ways to place the collocation points are considered. The numerical results for the problems of circular hole and circular elastic inclusion in infinite plate indicated that the appropriate choice of the approximating functions leads to a high accuracy of the calculation. Applications of the new technique to geomechanics problems are discussed. © 1998 John Wiley & Sons, Ltd.
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  • 82
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    Integrated pest management reviews 2 (1997), S. 17-24 
    ISSN: 1572-9745
    Keywords: Integrated pest management ; biological control ; oilpalm ; tettigonids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The global production ofpalm oil has increased very rapidly, more than doubling between1970 and 1980. Oil palm is the second most important cash crop inPapua New Guinea (PNG), and in 1995 its export value wasUS$128 million. The principal pests of oil palm in PNG are agroup of tettigonids, collectively known as Sexava, which causedamage by defoliating the oil palm tree. Severe defoliationcauses reductions in photosynthesis and fruit production,resulting in yield losses. Control of these pests is currentlyreliant upon the use of trunk-injected monocrotophos. Because ofdifficult application methods, poor monitoring procedures, andthe difficult environment, chemical control usually occurs toolate to prevent significant yield losses. Furthermore theapplication of chemicals is expensive and environmentallyundesirable. There is enormous potential to improve the currentpest management practices, and several biological control agentscould be used in an integrated pest management (IPM) system.Agronomic practices directed towards developing biodiversitywithin the oil palm cropping system, and improved pest monitoringand surveying could also be components of this IPMscheme
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  • 83
    ISSN: 1572-9745
    Keywords: Chenopodiumalbum ; Ascochyta caulina ; biological control ; microbialherbicide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 84
    ISSN: 1871-4528
    Keywords: suberin ; suberization ; lenticel penetration ; Erwinia carotovora ssp.atroseptica ; tuber development ; Solanum tuberosum L. ; biological control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Using the fluorescent lipid stain fluorol yellow 088 to detect suberin in tubers, the numbers of layers and the thickness of the suberized cells in the periderm and within the lenticels showed changes after the early stage of tuber formation. These changes as tubers matured were affected by cultivar and soil moisture conditions. Penetration of the surface tissues of tubers by the water soluble stain safranin O was confined to the lenticles. Although the zone of suberized cells in lenticels acted to some extent as a barrier to penetration, there was not a clear relationship between permeability and suberization. Stored tubers showed thicker suberin berriers in lenticels than freshly harvested tubers. When lenticels of stored tubers proliferated the suberin barrier was disrupted but a further thick suberin barrier formed after exposure to air for two weeks. The findings are discussed in relation to biological control ofErwinia by antagonistic bacteria.
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  • 85
    ISSN: 1573-8469
    Keywords: antagonism ; biological control ; fungicide ; GUS-transformant ; root colonization ; synergism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract There were indications that endo-1,3-β-glucanase (1,3-(1,3;1,4)-β-D-Glucan 3(4)-glucanohydrolase (EC 3.2.1.6)) and cellulase (1,4-(1,3;1,4)-β-D-Glucan 4-glucanohydrolase (EC 3.2.1.4)) activity of Trichoderma harzianum Rifai isolate T3 were induced in sphagnum peat moss cultivations and dual culture experiments by the presence of Pythium ultimum. Further, P. ultimum stimulated the germination of Trichoderma conidia. Endo-1,3-β-glucanase and cellulase were purified from T. harzianum isolate T3, known to control Pythium damping-off of cucumber seedlings. The enzymes were purified from the culture filtrate of the fungus by gel filtration and isoelectric focusing. The purified endo-1,3-β-glucanase was a small protein with a molecular mass of 17 kilodaltons and a pI of 5.0. Two cellulases were purified to homogeneity and had molecular masses of 40 and 45 kilodaltons respectively, and pI's of 6.4 and 7.6 respectively. Germination of encysted zoospores and elongation of germ tubes of a plant pathogenic Pythium isolate were inhibited by low concentrations of the purified enzymes. A strong synergistic effect was observed on the inhibition of cyst germination by a combination of the endo-1,3-β-glucanase and the fungicide Fongarid. Finally, a time-course study of colonization of the rhizosphere of cucumber seedlings showed that the active fungal mycelial biomass of a GUS-transformant of T. harzianum isolate T3 increased over four weeks. Trichoderma appeared to colonize healthy roots only superficially, whereas the mucilage of the root hairs and of distal parts of wounded areas or broken parts of the roots, were extensively colonized.
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  • 86
    ISSN: 1573-8469
    Keywords: antagonists ; biological control ; comparative screening ; field screening ; rhizosphere competence ; field performance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Different screening methods for selection of biological control agents (BCAs), for controlling soil and seed-borne diseases, are discussed. The shortcomings of laboratory methods focused on mechanism of action are discussed and we conclude that these methods should be used with caution if candidates with multifactorial or plant mediated mechanisms of control are to be obtained. In vitro screens may be useful for specific groups of microorganisms, thus, screens for antibiotics may be relevant for Streptomyces spp., and promising results have been obtained using soil plating or precolonized agar methods to screen for mycoparasitism and competitive saprophytic ability. Experience with screening in the Nordic programme ‘Biological control of seed borne diseases in cereals’ is summarized. Research in the four participating countries – Finland, Sweden, Norway and Denmark – followed the same paradigm: that of obtaining antagonists, well adapted to different Nordic environments, and developing them as effective BCAs. Potential antagonists were isolated from different sources and in planta screening methods were developed in order to optimize selection of antagonists effective against a range of seed borne pathogens. Screens in the laboratory or greenhouse were followed by screening in the field. The different screening procedures are compared and evaluated.
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  • 87
    ISSN: 1573-8469
    Keywords: antagonism ; apple scab ; biological control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract As part of an ongoing research project on biological control of apple scab, this study presents a novel approach for the in vitro selection of potential antagonists of the saprophytic phase of Venturia inaequalis. A collection of forty-two fungal isolates were tested for their in vitro ability to degrade apple leaf tissue, inhibit pseudothecia, and ascospore production. The inhibition of ascospore production cannot always be linked reliably with leaf degradation or the evaluation of pseudothecia production. Consequently, ascospore production was retained as the most useful screening parameter. Six isolates proved to significantly reduce the ascospore production of Venturia inaequalis. Two were as effective as Athelia bombacina, a previously reported antagonist of pseudothecia formation and inhibited over 98% of the ascospore production. These new organisms are now available for future field tests. Future selections from a large collection of fungal and bacterial saprophytes can now be based on a reliable and simple in vitro screening method.
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  • 88
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    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 43-72 
    ISSN: 0363-9061
    Keywords: plasticity ; contaminated clays ; organic contaminants ; chemical consolidation ; chemical swelling ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Isothermal chemo-elasto-plasticity of clays is discussed, to describe strains induced in clay by permeation of it with a low dielectric constant organic contaminant, in the presence of stress. The strain is crucial in controlling permeability changes in chemically affected clay barriers of landfills and impoundments. The theory encompasses chemical softening or yield surface reduction, coefficient of chemical reversible expansion or contraction due to mass concentration increase, as well as chemical sensitivity of bulk plastic modulus. The experiments on chemistry and stress dependent permeability of Sarnia clay performed by Fernandez and Quigley (1985, 1991) are interpreted using this model. The numerical representations of the chemo-plastic softening function and the chemo-elastic strain function, as well as plastic bulk modulus sensitivity to concentration are evaluated for dioxane and ethanol. Specific requirements for the tests for chemo-plastic behavior of clays are discussed. © 1997 by John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 121-132 
    ISSN: 0363-9061
    Keywords: thermoporoelasticity ; coupling ; decoupling ; consolidation ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Based on a fully coupled thermoporoelastic formulation, this paper discusses the general conditions where the coupling should be maintained, and where a partial or full decoupling technique may be applied. This exercise is aimed at providing practical solutions for the coupled thermoporoelastic analyses where excessive manipulations and unreasonable simplifications are minimized. The necessity for full coupling and the justification for decoupling are illustrated in a thermoporoelastic application of a one-dimensional consolidation scenario. © 1997 by John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 153-174 
    ISSN: 0363-9061
    Keywords: constitutive model ; hypoplasticity ; failure ; stability ; granular material ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Recent investigations on the hypoplastic constitutive model for granular materials show that the failure surface can be surpassed by some stress paths. This is contradictory to the conventional definition of failure surface in plasticity, according to which the stress is allowed to move on the failure surface but never across it. In the present paper, the interrelations among the different constitutive models are discussed with special reference to failure and stability. For the hypoplastic constitutive equation, the accessible stress states and the stable stress states are found to be enclosed by a bound surface and a stability surface in the stress space, respectively. Theoretical findings about the bound surface and the stability surface are verified qualitatively by presenting results of triaxial tests on dry sand. © 1997 by John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 241-253 
    ISSN: 0363-9061
    Keywords: rockbolt ; Euler-Bernoulli ; beam-column ; roof-reinforcement ; stability ; pull-out ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A simple analytical procedure that applies classical beam-column theory for evaluating passive rockbolt roof reinforcement is presented in this paper. The analytical model is derived from first principles and is capable of modelling any number of reinforcing bolts. Each rockbolt is modelled as a linear spring and the model allows for non-uniform bolt spacing. In this study the rock beam is assumed to be isotropic and linearly elastic for the sake of simplicity. However, the analytical model can be extended to include anisotropic rockmass as well as inelastic material behaviour. The solution to the coupled set of governing equations is obtained by using a simple numerical solution procedure. The results from the analytical model indicate that the critical buckling load of a rock beam is strongly influenced by the ambient rock modulus. For salt-rock excavations the rock modulus typically declines with time due to various phenomena, and a diminished modulus could seriously compromise roof stability. The other main conclusion of this study is that rockbolts loose their effectiveness in restraining a roof beam once its critical buckling load is approached. In such a situation, increasing bolt stiffness does not improve its reinforcing action on a roof beam but it enhances the possibility of bolt failure due to anchor pull-out. © 1997 by John Wiley & Sons, Ltd. Int. J. Numer. Anal. Meth. Geomech., vol. 21, 241-253 (1997)
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    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 347-358 
    ISSN: 0363-9061
    Keywords: packing ; elliptical ; particle ; assemblies ; simulation ; micromechanics ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: In this paper, a new generator algorithm and a computer program PG2D is introduced for 2D numerical simulation of packing configuration in a granular material composed of elliptical particles of different a/b aspect ratios. Each elliptical particle is approximated by four connected arcs. The centre co-ordinates and radius of each arc and co-ordinates of connecting points can be determined from the formulae derived by entering the major axis length, 2a, and the eccentricity. The domain to be filled with particles can be a polygon of any shape. Given the size of the packing domain, geometrical information and numbers of particles to be generated, the packing location of each particle and the co-ordinates of contact points along with contact normal rose diagram can be generated as outputs.Simulation results show that this new algorithm can provide quite a reasonable packing model in accordance with the initial input required for the analysis of the mechanics of granular material. This generation scheme has the potential to cover packing generation and behaviour analysis of 3D sphere or ellipsoidal shaped granular materials. © 1997 by John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 409-419 
    ISSN: 0363-9061
    Keywords: parallel numerical finite difference model ; heat and moisture transfer ; parallel computing ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A parallel numerical finite difference model, employing the self-implicit method, for coupled heat and moisture transfer in unsaturated soil is presented. The model is programmed in Occam and executed on a parallel computing network of transputers. An assessment of the model was achieved via the simulation of a laboratory experiment. A very good correlation between experimental and numerical results was obtained. Comparison of results with those obtained from a parallel explicit method is also illustrated showing no significant difference. The computational time employing the new method was, however, found to be half of that obtained using the explicit method. The computational efficiency of the approach was also found to be very high. © 1997 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 485-494 
    ISSN: 0363-9061
    Keywords: finite element method ; ground water ; phreatic surface ; transient flow ; unconfined seepage ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Peformance of rectangular trench drains penetrating fully in a layer of homogeneous and isotropic soil mass down to an underlying impervious base with time has been assessed using the finite element method. Non-dimensional charts have been developed comprehensively to establish the successive positions of a phreatic surface with the passage of time for any given values of permeability of soil and its specific yield. The effect of spacing to depth ratios of drains on their performance has been examined in detail. The rate of downward movements of the phreatic surface decreases with time as well as with increases in the spacing of drains. The spacing affects considerably the magnitudes of drawdown at distant locations from the drains, whereas close to the drains, its effect becomes insignificant. © 1997 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 453-475 
    ISSN: 0363-9061
    Keywords: consolidation ; settlement ; large strain ; numerical modelling ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper presents a piecewise-linear finite-difference model for one-dimensional large strain consolidation called CS2. CS2 is developed using a fixed Eulerian co-ordinate system and constitutive relationships which are defined by discrete data points. The model is dimensionless such that solutions are independent of the initial height of the compressible layer and the absolute magnitude of the hydraulic conductivity of the soil. The capability of CS2 is illustrated using four example problems involving small strain, large strain, self-weight, and non-linear constitutive relationships. In each case, the performance of the model is comparable to other available analytical and numerical solutions. Using CS2, correction factors are developed for the conventional Terzaghi theory which account for the effect of vertical strain on computed values by elapsed time and maximum excess pore pressure during consolidation. © 1997 John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 569-579 
    ISSN: 0363-9061
    Keywords: layered rock ; heterogeneity ; method of averaging ; variation-difference method ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The main purpose of this investigation is to study the state of stress of layered rocks forming slopes of deep river valleys. For this purpose averaging technique and a variant of the Variation-Difference Method are used. Because of the averaging method, equivalent homogeneous properties of layered elastic medium are determined. The paper has two parts. The first one is devoted to the analysis of a static stress-strain state of the slopes under gravity. The rock mass in the second part is subjected to dynamic loading caused by an earthquake. As a result of the numerical solution of the raised problems, the stress distribution in slopes and at the base of a deep canyon-like river valley was obtained. © 1997 John Wiley & Sons, Ltd.
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  • 97
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    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 583-597 
    ISSN: 0363-9061
    Keywords: finite elements ; soil nailing ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A nailed soil wall curved in plan was modelled in three-dimensions by the finite element method for construction, service and ultimate loading conditions. The behaviour of the nailed soil wall, the soil-nail interaction, the role of the reinforcement, and the overall and internal failure mechanisms were investigated. © 1997 by John Wiley & Sons, Ltd.
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    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 741-752 
    ISSN: 0363-9061
    Keywords: vertical deformation analysis ; pile group ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A variational approach for the analysis of vertical deformation of pile groups is presented. The method assumes that the deformation of piles can be represented by a finite series. The method applies the principle of minimum potential energy to determine the deformation of piles. Using this method, an analytical solution for pile groups in soil modelled by the theoretical load-transfer curves can be obtained rigorously. Analysis of field tests indicates that the method can predict the performance of pile groups reasonably well.
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    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 73-73 
    ISSN: 0363-9061
    Keywords: Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: No Abstract
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    International Journal for Numerical and Analytical Methods in Geomechanics 21 (1997), S. 91-120 
    ISSN: 0363-9061
    Keywords: finite elements ; oil migration ; immiscible two-phase flow ; compaction ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The upstream-weighted finite element method with lumped mass matrix is applied to the modelling of oil migration in compacting sedimentary basins. An implicit formulation is made in Lagrangian co-ordinates of a pressure, saturation and a temperature equation, which is based on immiscible two-phase flow of oil and water. The formulation accounts for the compaction of the sediments, the generation of oil from solid organic material (kerogen), the eventual pore space generated by kerogen breakdown, and the density variations of the fluids which may set up thermal convection. The model is validated by comparison with results from a one-dimensional (1D) fractional flow-based migration model. A 2D case example showing oil expulsion from source rocks, and the filling of a trap is presented. The mass balance of the model is easily checked because all oil in the basin originates from breakdown of kerogen. Compared with other alternatives, the simple upstream-weighted finite element method is suggested as a possible first choice for a numerical method for the modelling of oil migration in compacting sedimentary basins. It easily deals with the complex geometry of a basin, it yields reasonably good results, is simple to implement, and the same implementation applies to all spatial dimensions. © 1997 by John Wiley & Sons, Ltd.
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