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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Biogeochemistry 47 (1999), S. 15-23 
    ISSN: 1573-515X
    Keywords: ethane ; groundwater ; methane ; propane ; redox ; soil gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract This study investigates the presence and concentration of light hydrocarbon gases in soil vapor located immediately above the capillary fringe of a petroleum-contaminated aquifer. A correlation was observed for the linear regression plot of redox potential versus detectable C2+C3 alkane concentrations for a limited number of sampling points. C2+C3 alkanes were not detected at points were redox potentials in groundwater exceeded --260 millivolts. The predominance of methanogenic processes in this redox range, as well as the observed C2+C3 concentration ratios, suggest that ethane and propane gases in soil vapor may be biogenically produced as well as a result of volatilization from NAPL.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Biogeochemistry 47 (1999), S. 15-23 
    ISSN: 1573-515X
    Keywords: ethane ; groundwater ; methane ; propane ; redox ; soil gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract This study investigates the presence and concentration of light hydrocarbon gases in soil vapor located immediately above the capillary fringe of a petroleum-contaminated aquifer. A correlation was observed for the linear regression plot of redox potential versus detectable C2+C3 alkane concentrations for a limited number of sampling points. C2+C3 alkanes were not detected at points were redox potentials in groundwater exceeded -260 millivolts. The predominance of methanogenic processes in this redox range, as well as the observed C2+C3 concentration ratios, suggest that ethane and propane gases in soil vapor may be biogenically produced as well as a result of volatilization from NAPL.
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  • 3
    ISSN: 1573-515X
    Keywords: Atlantic ; ethylene ; methane ; sea-air exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The vertical distributions of ethylene and methane in the upper water column of the subtropical Atlantic were measured along a transect from Madeira to the Caribbean and compared with temperature, salinity, oxygen, nutrients, chlorophyll-a, and dissolved organic carbon (DOC). Methane concentrations between 41.6 and 60.7 nL L−1 were found in the upper 20 m of the water column giving a calculated average flux of methane into the atmosphere of 0.82μg m−2 h−1. Methane profiles reveal several distinct maxima in the upper 500 m of the water column and short-time variations which are presumably partly related to the vertical migration of Zooplankton. Ethylene concentrations in near surface waters varied in the range of 1.8 to 8.2 nL L−1. Calculated flux rates for ethylene into the atmosphere were in the range of 0.41 to 1.35μg m−2 h−1 with a mean of 0.83μg m−2h−2. Maximum concentrations of up to 39.2 nL L−2 were detected directly below the pycnocline in the western Atlantic. The vertical distributions of ethylene generally showed one maximum at the pycnocline (about 100 m depth) where elevated concentrations of chlorophyll-a, dissolved oxygen, and nutrients were also found; no ethylene was detected below 270 m depth. This suggests that ethylene release is mainly related to one, probably phytoplankton associated, source, while for methane, enhanced net production occurs at various depth horizons. For surface waters, a simple correlation between ethylene and chlorophyll-a or DOC concentrations could not be observed. No considerable diurnal variation was observed for the distribution and concentration of ethylene in the upper water column.
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  • 4
    ISSN: 1573-515X
    Keywords: grassland ; methane ; peat ; spatial variability ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane (CH4) emissions from soils, representing the consequence of CH4 production, CH4 consumption and CH4 transport, are poorly characterised and show a large spatial variability. This study aimed to assess the determinants of field-scale spatial variability of CH4 emissions from wet grasslands on peat soil. Mean CH4 emission rates of a three-year experiment at 18 plots distributed over three sites in the nature preserve “Nieuwkoopse Plassen” on peat soil in the Netherlands were related to CH4 production and CH4 consumption capacities of soil layers, and to soil and vegetation characteristics. Spatial variability of CH4 emissions and possible determining factors was high. Annual CH4 emissions ranged from 3 to 37 g CH4 m-2 yr-1. Coefficients of variation (CV) of CH4 emissions were on average 37% among sites and 83% within sites. Most important determinants of spatial variability were CH4 production capacity (average: 211 ng CH4 g-1 dry soil h-1; CV: 131%) and aboveground biomass of sedges (Carex spp.) (average: 0.45 g dm-2; CV: 127%) (P 〈 0.01). Sedges may affect CH4 emissions by stimulating CH4 transport from anaerobic layers to the surface via their vascular system and/or by serving as substrate for methanogens. For extrapolation of CH4 emissions to larger areas, best results will be obtained by using factors that are easy to determine, like vegetation.
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  • 5
    ISSN: 1573-515X
    Keywords: grassland ; ground water level ; methane ; peat ; temperature ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The area of wet grasslands on peat soil in the Netherlands is slowly increasing at the expense of drained, agriculturally used grasslands. This study aimed (i) to assess the contribution of wet grasslands on peat soil to methane (CH4) emissions, and (ii) to explain differences among sites and between years in order to improve our understanding of controlling factors. For these purposes, a field study was conducted in the period 1994–1996 in the nature preserve “Nieuwkoopse Plassen”, which is a former peat mining and agricultural area. Net CH4 emissions were measured weekly to monthly with vented closed flux chambers at three representative sites, and at ditches near these sites. Three-years average of CH4 emissions was 7.9 g CH4 m- 2 yr-1 for Drie Berken Zudde, 13.3 for Koole, and 20.4 for Brampjesgat. Ditches near the sites emitted 4.2–22.5 g CH4 m-2 yr-1. The time-course of CH4 emissions for all experimental sites and years was fit with a multiple linear regression model with ground water level and soil temperature as independent variables. Lowering or raising the ground water level by 5 cm could decrease or increase CH4 emissions by 30–50%. Therefore, ground water level management of these grasslands should be done with care.
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  • 6
    ISSN: 1573-515X
    Keywords: climate ; methane ; N2O ; Puerto Rico ; soil oxygen ; soil phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We measured soil oxygen concentrations at 10 and 35 cm depths and indices of biogeochemical cycling in upland forest soils along a rainfall and elevation gradient (3500–5000 mm y−1; 350–1050 masl) and along topographic gradients (ridge to valley, ∼150 m) in the Luquillo Experimental Forest, Puerto Rico. Along the rainfall gradient, soil O2 availability decreased significantly with increasing annual rainfall, and reached very low levels (〈3%) in individual chambers for up to 25 consecutive weeks over 82 weeks of study. Along localized topographic gradients, soil O2 concentrations were variable and decreased significantly from ridges to valleys. In the valleys, up to 35% of the observations at 10–35 cm depth were 〈3% soil O2. Cross correlation analyses showed that soil O2 concentrations were significantly positively correlated along the topographic gradient, and were sensitive to rainfall and hydrologic output. Soil O2 concentrations in valley soils were correlated with rainfall from the previous day, while ridge sites were correlated with cumulative rainfall inputs over 4 weeks. Soils at the wettest point along the rainfall gradient had very high soil methane concentrations (3–24%) indicating a strong influence of anaerobic processes. We measured net methane emission to the atmosphere at the wettest sites of the rainfall gradient, and in the valleys along topographic gradients. Other measures of biogeochemical function such as soil organic matter content and P availability were sensitive to chronic O2 depletion along the rainfall gradient, but less sensitive to the variable soil O2 environment exhibited at lower elevations along topographic gradients.
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  • 7
    ISSN: 1573-515X
    Keywords: alpine tundra ; methane ; trace gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We measured CH4 fluxes from three major plant communities characteristic of alpine tundra in the Colorado Front Range. Plant communities in this ecosystem are determined by soil moisture regimes induced by winter snowpack distribution. Spatial patterns of CH4 flux during the snow-free season corresponded roughly with these plant communities. InCarex-dominated meadows, which receive the most moisture from snowmelt, net CH4 production occurred. However, CH4 production in oneCarex site (seasonal mean=+8.45 mg CH4 m−2 d−1) was significantly larger than in the otherCarex sites (seasonal means=−0.06 and +0.05 mg CH4 m−2 d−1). This high CH4 flux may have resulted from shallower snowpack during the winter. InAcomastylis meadows, which have an intermediate moisture regime, CH4 oxidation dominated (seasonal mean=−0.43 mg CH4 m−2 d−1). In the windsweptKobresia meadow plant community, which receive the least amount of moisture from snowmelt, only CH4 oxidation was observed (seasonal mean=−0.77 mg CH4 m−2 d−1). Methane fluxes correlated with a different set of environmental factors within each plant community. In theCarex plant community, CH4 emission was limited by soil temperature. In theAcomastylis meadows, CH4 oxidation rates correlated positively with soil temperature and negatively with soil moisture. In theKobresia community, CH4 oxidation was stimulated by precipitation. Thus, both snow-free season CH4 fluxes and the controls on those CH4 fluxes were related to the plant communities determined by winter snowpack.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Biogeochemistry 47 (1999), S. 187-202 
    ISSN: 1573-515X
    Keywords: boreal peatland ; floating peat ; methane ; reservoirs ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The effect of flooding on methane (CH4) fluxes was studied through the construction of an experimental reservoir in a boreal forest wetland at the Experimental Lakes Area in northwestern Ontario. Prior to flooding, the peatland surface was a small source of CH4 to the atmosphere (1.0 ± SD of 2.3 mg CH4 m−2 d−1). After flooding, CH4 fluxes from the submerged peat surface increased to 64±68 mg CH4 m−2 d−1. CH4 bubbles within the submerged peat caused about 1/3 of the peat to float. Fluxes from these floating peat islands were much higher (440±350 mg CH4 m−2 d−1) than from both the pre-flood (undisturbed) and the post-flood (submerged) peat surfaces. The high fluxes of CH4 from the floating peat surfaces may be explained by a number of factors known to affect the production and consumption of CH4 in peat. In floating peat, however, these factors are particularly enhanced and include decreased oxidation of CH4 due to the loss of aerobic habitat normally found above the water table of undisturbed peat and to increased peat temperatures. The extremely high fluxes associated with newly lifted peat may decrease as the islands age. However, CH4 flux rates from floating peat islands that were several years old still far exceeded those from undisturbed peat surfaces and from the water surface of a newly created reservoir.
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  • 9
    Electronic Resource
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    Springer
    Biogeochemistry 47 (1999), S. 187-202 
    ISSN: 1573-515X
    Keywords: boreal peatland ; floating peat ; methane ; reservoirs ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The effect of flooding on methane (CH4) fluxes was studied through the construction of an experimental reservoir in a boreal forest wetland at the Experimental Lakes Area in northwestern Ontario. Prior to flooding, the peatland surface was a small source of CH4 to the atmosphere (1.0± SD of 2.3 mg CH4 m−2 d−1). After flooding, CH4 fluxes from the submerged peat surface increased to 64±68 mg CH4 m−2 d−1 CH4 bubbles within the submerged peat caused about 1/3 of the peat to float. Fluxes from these floating peat islands were much higher (440±350 mg CH4 m−2 d−2) than from both the pre-flood (undisturbed) and the post-flood (submerged) peat surfaces. The high fluxes of CH4 from the floating peat surfaces may be explained by a number of factors known to affect the production and consumption of CH4 in peat. In floating peat, however, these factors are particularly enhanced and include decreased oxidation of CH4 due to the loss of aerobic habitat normally found above the water table of undisturbed peat and to increased peat temperatures. The extremely high fluxes associated with newly lifted peat may decrease as the islands age. However, CH4 flux rates from floating peat islands that were several years old still far exceeded those from undisturbed peat surfaces and from the water surface of a newly created reservoir.
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  • 10
    ISSN: 1573-515X
    Keywords: alpine tundra ; methane ; trace gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We measured CH4 fluxes from three major plant communities characteristic of alpine tundra in the Colorado Front Range. Plant communities in this ecosystem are determined by soil moisture regimes induced by winter snowpack distribution. Spatial patterns of CH4 flux during the snow-free season corresponded roughly with these plant communities. In Carex-dominated meadows, which receive the most moisture from snowmelt, net CH4 production occurred. However, CH4 production in one Carex site (seasonal mean = +8.45 mg CH4 m-2 d-1) was significantly larger than in the other Carex sites (seasonal means = –0.06 and +0.05 mg CH4 m-2 d-1). This high CH4 flux may have resulted from shallower snowpack during the winter. In Acomastylis meadows, which have an intermediate moisture regime, CH4 oxidation dominated (seasonal mean = –0.43 mg CH4 m-2 d-1). In the windswept Kobresia meadow plant community, which receive the least amount of moisture from snowmelt, only CH4 oxidation was observed (seasonal mean = –0.77 mg CH4 m-2 d-1). Methane fluxes correlated with a different set of environmental factors within each plant community. In the Carex plant community, CH4 emission was limited by soil temperature. In the Acomastylis meadows, CH4 oxidation rates correlated positively with soil temperature and negatively with soil moisture. In the Kobresia community, CH4 oxidation was stimulated by precipitation. Thus, both snow-free season CH4 fluxes and the controls on those CH4 fluxes were related to the plant communities determined by winter snowpack.
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  • 11
    ISSN: 1573-515X
    Keywords: Atlantic ; ethylene ; methane ; sea-air exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The vertical distributions of ethylene and methane in the upper water column of the subtropical Atlantic were measured along a transect from Madeira to the Caribbean and compared with temperature, salinity, oxygen, nutrients, chlorophyll-a, and dissolved organic carbon (DOC). Methane concentrations between 41.6 and 60.7 nL L-1 were found in the upper 20 m of the water column giving a calculated average flux of methane into the atmosphere of 0.82 μg m-2 h-1. Methane profiles reveal several distinct maxima in the upper 500 m of the water column and short-time variations which are presumably partly related to the vertical migration of zooplankton. Ethylene concentrations in near surface waters varied in the range of 1.8 to 8.2 nL L-1. Calculated flux rates for ethylene into the atmosphere were in the range of 0.41 to 1.35 μg m-2 h-1 with a mean of 0.83 μg m-2 h-1. Maximum concentrations of up to 39.2 nL L-1 were detected directly below the pycnocline in the western Atlantic. The vertical distributions of ethylene generally showed one maximum at the pycnocline (about 100 m depth) where elevated concentrations of chlorophyll-a, dissolved oxygen, and nutrients were also found; no ethylene was detected below 270 m depth. This suggests that ethylene release is mainly related to one, probably phytoplankton associated, source, while for methane, enhanced net production occurs at various depth horizons. For surface waters, a simple correlation between ethylene and chlorophyll-a or DOC concentrations could not be observed. No considerable diurnal variation was observed for the distribution and concentration of ethylene in the upper water column.
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  • 12
    ISSN: 1573-515X
    Keywords: carbon dioxide ; gas gradients ; methane ; nitrous oxide ; peatland ; winter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract CO2 and CH4 fluxes during the winter were measured at natural and drained bog and fen sites in eastern Finland using both the closed chamber method and calculations of gas diffusion along a concentration gradient through the snowpack. The snow diffusion results were compared with those obtained by chamber, but the winter flux estimates were derived from chamber data only. CH4 emissions from a poor bog were lower than those from an oligotrophic fen, while both CO2 and CH4 fluxes were higher in the Carex rostrata-occupied marginal (lagg) area of the fen than in the slightly less fertile centre. Average estimated winter CO2-C losses from virgin and drained forested peatlands were 41 and 68 g CO2-C m- 2, respectively, accounting for 23 and 21% of the annual total CO2 release from the peat. The mean release of CH4-C was 1.0 g in natural bogs and 3.4 g m-2 in fens, giving rise to winter emissions averaging to 22% of the annual emission from the bogs and 10% of that from the fens. These wintertime carbon gas losses in Finnish natural peatlands were even greater than reported average long-term annual C accumulation values (less than 25 g C m-2). The narrow range of 10–30% of the proportion of winter CO2 and CH4 emissions from annual emissions found in Finnish peatlands suggest that a wider generalization in the boreal zone is possible. Drained forested bogs emitted 0.3 g CH4-C m-2 on the average, while the effectively drained fens consumed an average of 0.01 g CH4-C m- 2. Reason for the low CH4 efflux or net oxidation in drained peatlands probably lies in low substrate supply and thus low CH4 production in the anoxic deep peat layers. N2O release from a fertilized grassland site in November–May was 0.7 g N2O m-2, accounting for 38% of the total annual emission, while a forested bog released none and two efficiently drained forested fens 0.09 (28% of annual release) and 0.04 g N2O m- 2 (27%) during the winter, respectively.
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  • 13
    ISSN: 1573-515X
    Keywords: carbon dioxide ; gas gradients ; methane ; nitrous oxide ; peatland ; winter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract CO2 and CH4 fluxes during the winter were measured at natural and drained bog and fen sites in eastern Finland using both the closed chamber method and calculations of gas diffusion along a concentration gradient through the snowpack. The snow diffusion results were compared with those obtained by chamber, but the winter flux estimates were derived from chamber data only. CH4 emissions from a poor bog were lower than those from an oligotrophic fen, while both CO2 and CH4 fluxes were higher in theCarex rostrata- occupied marginal (lagg) area of the fen than in the slightly less fertile centre. Average estimated winter CO2-C losses from virgin and drained forested peatlands were 41 and 68 g CO2-C m−2, respectively, accounting for 23 and 21% of the annual total CO2 release from the peat. The mean release of CH4-C was 1.0 g in natural bogs and 3.4 g m−2 in fens, giving rise to winter emissions averaging to 22% of the annual emission from the bogs and 10% of that from the fens. These wintertime carbon gas losses in Finnish natural peatlands were even greater than reported average long-term annual C accumulation values (less than 25g C m−2). The narrow range of 10–30% of the proportion of winter CO2 and CH4 emissions from annual emissions found in Finnish peatlands suggest that a wider generalization in the boreal zone is possible. Drained forested bogs emitted 0.3 g CH4-C m−2 on the average, while the effectively drained fens consumed an average of 0.01 g CH4-C m−2. Reason for the low CH4. efflux or net oxidation in drained peatlands probably lies in low substrate supply and thus low CH4 production in the anoxic deep peat layers. N2O release from a fertilized grassland site in November–May was 0.7 g N2O m−2, accounting for 38% of the total annual emission, while a forested bog released none and two efficiently drained forested fens 0.09 (28% of annual release) and 0.04 g N2O m−2 (27%) during the winter, respectively.
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  • 14
    Electronic Resource
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    Springer
    Biogeochemistry 44 (1999), S. 205-220 
    ISSN: 1573-515X
    Keywords: grassland ; ground water level ; methane ; peat ; temperature ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The area of wet grasslands on peat soil in the Netherlands is slowly increasing at the expense of drained, agriculturally used grasslands. This study aimed (i) to assess the contribution of wet grasslands on peat soil to methane (CH4) emissions, and (ii) to explain differences among sites and between years in order to improve our understanding of controlling factors. For these purposes, a field study was conducted in the period 1994–1996 in the nature preserve “Nieuwkoopse Plassen”, which is a former peat mining and agricultural area. Net CH4 emissions were measured weekly to monthly with vented closed flux chambers at three representative sites, and at ditches near these sites. Three-years average of CH4 emissions was 7.9 g CH4 m−2 yr−1 for Drie Berken Zudde, 13.3 for Koole, and 20.4 for Brampjesgat. Ditches near the sites emitted 4.2–22.5 g CH4 m−2 yr−1. The time-course of CH4 emissions for all experimental sites and years was fit with a multiple linear regression model with ground water level and soil temperature as independent variables. Lowering or raising the ground water level by 5 cm could decrease or increase CH4 emissions by 30–50%. Therefore, ground water level management of these grasslands should be done with care.
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  • 15
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    Springer
    Biogeochemistry 44 (1999), S. 221-237 
    ISSN: 1573-515X
    Keywords: grassland ; methane ; peat ; spatial variability ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane (CH4) emissions from soils, representing the consequence of CH4 production, CH4 consumption and CH4 transport, are poorly characterised and show a large spatial variability. This study aimed to assess the determinants of field-scale spatial variability of CH4 emissions from wet grasslands on peat soil. Mean CH4 emission rates of a three-year experiment at 18 plots distributed over three sites in the nature preserve “Nieuwkoopse Plassen” on peat soil in the Netherlands were related to CH4 production and CH4 consumption capacities of soil layers, and to soil and vegetation characteristics. Spatial variability of CH4 emissions and possible determining factors was high. Annual CH4 emissions ranged from 3 to 37 g CH4 m−2 yr−1. Coefficients of variation (CV) of CH4 emissions were on average 37% among sites and 83% within sites. Most important determinants of spatial variability were CH4 production capacity (average: 211 ng CH4 g−1 dry soil h−1; CV: 131%) and aboveground biomass of sedges (Carex spp.) (average: 0.45 g dm−2; CV: 127%) (P〈0.01). Sedges may affect CH4 emissions by stimulating CH4 transport from anaerobic layers to the surface via their vascular system and/or by serving as substrate for methanogens. For extrapolation of CH4 emissions to larger areas, best results will be obtained by using factors that are easy to determine, like vegetation.
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  • 16
    ISSN: 1573-515X
    Keywords: climate ; methane ; N2O ; Puerto Rico ; soil oxygen ; soil phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We measured soil oxygen concentrations at 10 and 35 cm depths and indices of biogeochemical cycling in upland forest soils along a rainfall and elevation gradient (3500–5000 mm y−1; 350–1050 masl) and along topographic gradients (ridge to valley, ∼150 m) in the Luquillo Experimental Forest, Puerto Rico. Along the rainfall gradient, soil O2 availability decreased significantly with increasing annual rainfall, and reached very low levels (〈3%) in individual chambers for up to 25 consecutive weeks over 82 weeks of study. Along localized topographic gradients, soil O2 concentrations were variable and decreased significantly from ridges to valleys. In the valleys, up to 35% of the observations at 10–35 cm depth were 〈3% soil O2. Cross correlation analyses showed that soil O2 concentrations were significantly positively correlated along the topographic gradient, and were sensitive to rainfall and hydrologic output. Soil O2 concentrations in valley soils were correlated with rainfall from the previous day, while ridge sites were correlated with cumulative rainfall inputs over 4 weeks. Soils at the wettest point along the rainfall gradient had very high soil methane concentrations (3–24%) indicating a strong influence of anaerobic processes. We measured net methane emission to the atmosphere at the wettest sites of the rainfall gradient, and in the valleys along topographic gradients. Other measures of biogeochemical function such as soil organic matter content and P availability were sensitive to chronic O2 depletion along the rainfall gradient, but less sensitive to the variable soil O2 environment exhibited at lower elevations along topographic gradients.
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  • 17
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    Climatic change 40 (1998), S. 277-284 
    ISSN: 1573-1480
    Keywords: ombrotrophic bogs ; microbial ecology ; methane ; climate change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Gases are produced from wetlands when plant biomass is degraded by microbial consortia, producing carbon dioxide aerobically and methane when oxygen is lacking. In anaerobic waterlogged situations, such as the catotelm of ombrotrophic bogs, this methane forms minute gas bubbles that severely reduce the hydraulic conductivity and hence the degradation of biomass due to the lack of nutrients. The bogs thus become carbon sinks, formed from the partially degraded biomass that accumulates as peat. The results of an investigation of an ombrotrophic bog, Mer Bleue, Ontario, Canada are summarized here, and the effects that climate change may have on such bogs are discussed. Any change of the water table in wetlands will have a substantial effect upon their ecology. If the water table should fall allowing bogs to become aerobic, most of the accumulated biomass carbon could be returned to the atmosphere by degradation to carbon dioxide, and as well, methane entrapped within the matrix would be released directly to the atmosphere. If on the other hand, the bogs are flooded, then the entrapped bubbles will coalesce allowing the gas to escape to the atmosphere, while at the same time the degradation of the peat will be enhanced.
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  • 18
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    Aquatic geochemistry 4 (1998), S. 403-427 
    ISSN: 1573-1421
    Keywords: methane ; trace gases ; North Sea ; air-sea exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The methane concentration in the atmosphere andsurface water was surveyed along 58° N acrossthe North Sea. In addition, the vertical methanedistribution in the water column was determined at sixstations along the transect. The methane contents ofthe surface water as well as in the water column wereextremely inhomogeneous. Input by freshwater fromriver discharge and injection of methane from thesediment were both observed. The survey continued fromthe western side of the North Sea to the Elbe Riverestuary. The Elbe River appears to have low methaneconcentrations compared to other European rivers, itsaverage input into the North Sea is estimated to be70 nmol s-1 of methane. Near 58° N,1°40' E, an abandoned drill site releases about 25 % ofthe North Sea's emission of methane to the atmosphere.The advective methane transport induced by watercirculation was assessed for May 16, 1994, using a 3-DNorth Sea circulation model. For the period of thissurvey, the North Sea's source strength foratmospheric methane is estimated using in situwind velocities. In comparison to the advectivetransport by the water circulation, the gas flux tothe atmosphere appears to be the dominant sink ofNorth Sea methane. This flux is estimated to bebetween 1500 · 106 mol a-1 and 3100 ·106mol a-1, depending on the relationbetween wind speed and gas transfer velocity.
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  • 19
    ISSN: 1573-515X
    Keywords: carbon dioxide ; hysteresis ; methane ; peat ; temperature ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The ability to predict the effects of climate change on trace gas fluxes requires a knowledge of microbial temperature responses. However, the response of a microbial community to temperature in a given substrate may be complicated by its thermal history. To examine the effect of sequentially changing temperature on methane and carbon dioxide production in different peat types, we incubated anaerobic peat samples from 3 types of northern peatlands, a bog, a sedge fen and a cedar swamp, in both rising and falling temperature regimes. Graphic and statistical comparisons of the different temperature regimes suggest hysteresis in microbial response to temperature, although the absolute rates at any given temperature often did not differ. Where regressions for temperature response (Arrhenius plots) were significant, they generally differed between temperature regimes. The greatest differences among treatments occurred during the first half of the 40-d incubation. Increases in carbon dioxide production were similar across all peat types, but methanogenesis varied widely: methane production was uniformly low in the bog peat but increased sharply with temperature in the other two peat types. The complicating effect of history or chronology on substrate responses to environmental stimuli may restrain our ability to model the responses of complex systems to changing conditions.
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  • 20
    ISSN: 1573-515X
    Keywords: drainage ; denitrification ; methane ; nitric oxide ; nitrous oxide ; nitrification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Intermittent drainage of rice fields isdiscussed as an option to mitigate emission ofCH4, an important greenhouse gas. HoweverN2O, a potentially more effective greenhouse gas,may be emitted during the aeration phase. Therefore,the metabolism of NO, N2O, NH $$_4^ + $$ ,NO $$_2^ - $$ and NO $$_3^ - $$ and the kinetics ofCH4 oxidation were measured after aeration ofmethanogenic rice field soil. Before aeration, thesoil contained NH $$_4^ + $$ in relatively highconcentrations (about 4 mM), while NO $$_2^ - $$ andNO $$_3^ - $$ were almost undetectable. Immediatelyafter aeration both NO and N2O were produced withrates of about 15 pmol h-1 gdw-1 and 5 pmolh-1 gdw-1, respectively. Simultaneously,NH $$_4^ + $$ decreased while NO $$_2^ - $$ accumulated. Later on, NO $$_2^ - $$ was depletedwhile NO $$_3^ - $$ concentrations increased.Characteristic phases of nitrogen turnover wereassociated with the activities of ammonium oxidizers,nitrite oxidizers and denitrifiers. Oxidation ofNH $$_4^ + $$ and production of NO and N2O wereinhibited by 10 Pa acetylene demonstrating thatnitrification was obligatory for the initiation ofnitrogen turnover and production of NO and N2O.Ammonium oxidation was not limited by the availableNH $$_4^ + $$ and thus, concomittant production of NOand N2O was not stimulated by addition ofNH $$_4^ + $$ . However, addition of NO $$_3^ - $$ stimulated production of NO and N2O in bothanoxic and aerated rice soil slurries. In this case,10 Pa acetylene did not inhibit the production of NOand N2O demonstrating that it was due todenitrification which was obviously limited by theavailability of NO $$_3^ - $$ . In the aerated soilslurries CH4 was only oxidized if present atelevated concentrations 〉50 ppmv CH4). Atatmospheric CH4 concentrations (∼1.7 ppmv)CH4 was not consumed, but was even slightly produced.CH4 oxidation activity increased afterpreincubation at 20% CH4, and then CH4was also oxidized at atmospheric concentrations. CH4oxidation kinetics exhibited sigmoid characteristicsat low CH4 concentrations presumably because ofinhibition of CH4 oxidation by NH $$_4^ + $$ .
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    Climatic change 40 (1998), S. 229-245 
    ISSN: 1573-1480
    Keywords: carbon ; carbon dioxide ; methane ; dissolved organic carbon ; peatlands ; climatic change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Northern peatlands play an important role globally in the cycling of C, through the exchange of CO2 with the atmosphere, the emission of CH4, the production and export of dissolved organic carbon (DOC) and the storage of C. Under 2 × CO2 GCM scenarios, most Canadian peatlands will be exposed to increases in mean annual temperature ranging between 2 and 6° C and increases in mean annual precipitation of 0 to 15 %, with the most pronounced changes occurring during the winter. The increase in CO2 uptake by plants, through warmer temperatures and elevated atmospheric CO2, is likely to be offset by increased soil respiration rates in response to warmer soils and lowered water tables. CH4 emissions are likely to decrease in most peatlands because of lowered water tables, except where the peat surface adjusts to fluctuating water tables, and in permafrost, where the collapse of dry plateau and palsa will lead to increase CH4 emission. There likely will be little change in DOC production, but DOC export to water bodies will decrease as runoff decreases. The storage of C in peatlands is sensitive to all C cycle components and is difficult to predict. The challenge is to develop quantitative models capable of making these predictions for different peatlands. We present some qualitative responses, with levels of uncertainty. There will be, however, as much variation in response to climatic change within a peatland as there will be among peatland regions.
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  • 22
    ISSN: 1573-0662
    Keywords: tropospheric chemistry ; ozone ; Russia ; trans-Siberian railroad ; Siberia ; carbon monoxide ; methane ; nitrogen oxides ; trace gases ; atmospheric composition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Using a laboratory wagon traveling along the Trans-Siberian railroad, O3, NO, NO2, CO, CH4, SF6 and black carbon aerosol have been measured during the summer of 1996. The expedition from Niznij Novgorod (500 km east of Moscow) to Vladivostok (and back to Moscow) has shown the great potential of the train method; here the first results are presented and discussed. A wealth of boundary layer air data was obtained during the over 18000 km travel without serious contamination problems from the electric train itself. The diurnal O3 cycle peaked generally below 50 nmole/mole, showed the effects of changes in J(NO2), and often dropped to a few nmole/mole at night time during inversions. Over the vast Siberian lowlands situated between the Ural mountains and the river Yenisey, CH4 levels were consistently elevated at around 1.95 µmole/mole, which we mainly attribute to wetland emissions. Over eastern Siberia, however, CH4 levels were generally lower at 1.85 µmole/mole. In contrast, over the west Siberian lowlands, CO levels were relatively low, often reaching values of only 110 nmole/mole, whereas over eastern Siberia CO levels were higher. Very high CO levels were detected over a 2000 km section east of Chita, along the river Amur, which represented an enormous polluted air mass. 14C analysis performed on several CO samples confirms that the origin was biomass burning. SF6, which was measured as a general conserved tracer, showed an eastward attenuation from 4.0 to 3.9 pmole/mole, with peaks in a number of places due to local Russian emissions.
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    Biogeochemistry 41 (1998), S. 215-235 
    ISSN: 1573-515X
    Keywords: arctic ; carbon dioxide ; climate change ; methane ; plant transport ; species composition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We conducted plant species removals, air temperaturemanipulations, and vegetation and soil transplants inAlaskan wet-meadow and tussock tundra communities todetermine the relative importance of vegetation typeand environmental variables in controlling ecosystemmethane (CH4) and carbon dioxide (CO2) flux. Plastic greenhouses placed over wet-meadow tundraincreased air temperature, soil temperature, and soilmoisture, but did not affect CH4 or CO2 flux(measured in the dark). By contrast, removal ofsedges in the wet meadow significantly decreased fluxof CH4, while moss removal tended to increaseCH4 emissions. At 15 cm depth, pore-waterCH4 concentrations were higher in sedge-removalthan in control plots, suggesting that sedgescontribute to CH4 emissions by transportingCH4 from anaerobic soil to the atmosphere, ratherthan by promoting methanogenesis. Inreciprocal-ecosystem transplants between thewet-meadow and tussock tundra communities, CH4and CO2 emissions were higher overall in thewet-meadow site, but were unrelated to transplantorigin. Methane flux was correlated with localvariation in soil temperature, thaw depth, andwater-table depth, but the relative importance ofthese factors varied through the season. Our resultssuggest that future changes in CH4 and CO2flux in response to climatic change will be morestrongly mediated by large-scale changes in vegetationand soil parameters than by direct temperature effects.
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  • 24
    ISSN: 1573-515X
    Keywords: carbon dioxide ; eastern Tennessee ; ecosystem metabolism ; methane ; streams ; Smoky Mountains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The partial pressures of CO2 (pCO2) andCH4 (pCH4) in streams are not only governed byinstream processes, but also by transformations occurring in soil andgroundwater ecosystems. As such, stream water pCO2 andpCH4 can provide a tool to assess ecosystem respiration andanaerobic metabolism throughout drainage basins. We conducted three surveyssampling the gas content of streams in eastern Tennessee and western NorthCarolina to assess factors regulating ecosystem metabolism in catchmentswith contrasting geomorphologies, elevations and soil organic matterstorage. In our first survey, the influence of drainage basin geomorphologyon ecosystem respiration was examined by sampling streams drainingcatchments underlain by either shale or dolomite. Geomorphology isinfluenced by geology with shale catchments having shallower soils, broader,unconstrained valley floors compared with dolomite catchments.pCO2 varied little between catchment types but increased froman average of 3340 ppmv in spring to 9927 ppmv in summer or 9.3 and 28 timesatmospheric equilibrium (pCO2(equilib)), respectively. Incontrast, pCH4 was over twice as high in streams drainingshale catchments (306 ppmv; pCH4(equilib) = 116) compared withmore steeply incised dolomite basins (130 ppmv; pCH4(equilib)= 51). Using the ratio of pCH4:pCO2 as an indexof anaerobic metabolism, shale catchments had nearly twice as muchanaerobiosis (pCH4:pCO2 = 0.046) than dolomitedrainages (pCH4:pCO2 = 0.024). In our secondsurvey, streams were sampled along an elevational gradient (525 to 1700 m)in the Great Smoky Mountains National Park, USA where soil organic matterstorage increases with elevation. pCO2 did not vary betweenstreams but increased from 5340 ppmv (pCO2(equilib) = 15) to8565 ppmv (pCO2(equilib) = 24) from spring to summer,respectively. During spring pCH4 was low and constant acrossstreams, but during summer increased with elevation ranging from 17 to 2068ppmv (pCH4(equilib) = 10 to 1216). The contribution ofanaerobiosis to total respiration was constant during spring(pCH4:pCO2 = 0.017) but during summer increasedwith elevation from 0.002 at 524 m to 0.289 at 1286 m. In our last survey,we examined how pCO2 and pCH4 changed withcatchment size along two rivers (ca. 60 km stretches in both riverscorresponding to increases in basin size from 1.7–477km2 and 2.5–275 km2). pCO2and pCH4 showed opposite trends, with pCO2decreasing ca. 50% along the rivers, whereas pCH4roughly doubled in concentration downstream. These opposing shifts resultedin a nearly five-fold increase of pCH4:pCO2along the rivers from a low of 0.012 in headwaters to a high of 0.266 65-kmdownstream. pCO2 likely declines moving downstream asgroundwater influences on stream chemistry decreases, whereaspCH4 may increase as the prevalence of anoxia in riversexpands due to finer-grained sediments and reduced hydrologic exchange withoxygenated surface water.
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    Biogeochemistry 37 (1997), S. 227-236 
    ISSN: 1573-515X
    Keywords: Louisiana USA ; wetlands ; methane ; methanogensis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane emissions from three wetland habitats in the MississippiRiver deltaic plain were measured over a three year period. Fluxdata collected indicate that each habitat was a net source of methane to the atmosphere throughout the year. Average emissionfrom a Taxodium distichum / Nyssa aquatica (bald cypress / watertupelo) swamp forest was 146 ± 199 mgCH4 m-2d-1 whileemissions from a Sagittaria lancifolia (bulltongue) freshwatermarsh averaged 251 ± 188 mg CH4m-2d-1. Methane flux from a Spartina patens / Sagittaria lancifolia intermediate marsh was significantlyhigher, 912 ± 923 mg CH4m-2d-1. Seasonal variation wassignificant with emissions being higher in the late summer andearly fall. Significant diurnal emissions were observed fromthe Sagittaria lancifolia marsh site. Soil temperature (5 and 10 cm depths) was found to be significantly correlated with methaneemission from the three sites.
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    Biogeochemistry 37 (1997), S. 77-88 
    ISSN: 1573-515X
    Keywords: climate change ; elevated carbon dioxide ; hydrology ; methane ; transpiration ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane emissions from wetland soils are generally a positive function ofplant size and primary productivity, and may be expected to increase dueto enhanced rates of plant growth in a future atmosphere of elevatedCO2. We performed two experiments with Orontium aquaticum, acommon emergent aquatic macrophyte in temperate and sub-tropical wetlands, todetermine if enhanced rates of photosynthesis in elevated CO2atmospheres would increase CH4 emissions from wetland soils.O. aquaticum was grown from seed in soil cores under ambient and elevated(ca. 2-times ambient) concentrations of CO2 in an initialglasshouse study lasting 3 months and then a growth chamber study lasting 6months. Photosynthetic rates were 54 to 71% higher underelevated CO2 than ambient CO2, but plantbiomass was not significantly different at the end of the experiment. Ineach case, CH4 emissions were higher under elevated thanambient CO2 levels after 2 to 4 months of treatment, suggestinga close coupling between photosynthesis and methanogenesis in our plant-soilsystem. Methane emissions in the growth chamber study increased by 136%. We observed a significant decrease in transpirationrates under elevated CO2 in the growth chamber study, andspeculate that elevated CO2 may also stimulate CH4 emissions by increasing the extent and duration offlooding in some wetland ecosystems. Elevated CO2 maydramatically increase CH4 emissions from wetlands, a sourcethat currently accounts for 40% of global emissions.
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  • 27
    ISSN: 1573-515X
    Keywords: aquatic marcrophytes ; methane ; methane oxidation ; methyl fluoride ; plant/microbial ; interactions ; rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane oxidation rates in the rhizosphere of Pontederia cordata,Sagittaria lancifolia, and Typha latifolia were quantified in fieldstudies using the methyl fluoride inhibition technique. An averageoxidation of 22.9 ± 17.7% (sd,n = 44) was found for all field experiments (oxidation is expressedas a % of total potential emission in the presumedabsence of oxidation). Greenhouse experiments using the same techniquegave an average rhizospheric oxidation of 64.9 ±17.0% (sd, n = 44). Comparison of a subset ofgreenhouse plants with the methyl fluoride (MF) and a light oxic/darkanoxic (LO/DA) technique for suppressing CH4 oxidationyielded similar percentages (57.7 ±15.0% for MF and 58.5 ±13.9% for LO/DA, n = 11). Rhizospheric oxidationdisplayed a seasonal trend in Typha latifolia with decreasingoxidation percentages during warmer months as the importance ofrhizospheric CH4 oxidation declined relative toCH4 emission (46.5 ±13.8% in December and 13.5 ±1.7% in July). However, the absolute rateof methane oxidation was highest during the warmer months (44.2± 3.4 mg m-2 d-1 inDecember and 318.7 ± 151.4 mg m-2d-1 in July). As methane emission rates increased,the sensitivity of the methyl fluoride technique decreased dueto the larger error between replicate flux measurements.
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  • 28
    ISSN: 1573-515X
    Keywords: die-back ; methane ; methanogenesis ; Phragmites australis ; rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methanogenesis was measured during the summer of 1994, in sediment coresand bulk samples from a Phragmites australis wetland in northern Jutland,Denmark. We compared sediment from healthy reed and dying-back reed, andan open lagoon resulting from die-back. Cores revealed variability withdepth and between sites, with the highest rates coinciding with layers oforganic gyttja, and negligible methane production from the underlying sandbase. Methanogenesis rates in the lagoon and die back sites were higher(up to 100–150 nmol h-1 g-1dry wt. sediment) than in the healthy reed (50–80 nmolh-1 g-1), with the highest rates being recordedfrom May to July. At these times, methanogenesis was markedly temperature-limited; samples incubated at 30 °C anon-limiting temperature, gave rates as high as 200–400nmol h-1 g-1 for the lagoon and die-backareas and 150 nmol h-1 g-1 for the healthyarea. Addition of 8 mM acetate and H2/CO2headspace suggested that both acetate-fermenting andCO2-reducing bacteria were present. Acetate additions suggested some co-limitation by substrate availability, with acetate limitation occurring in the healthy site during July and in the die-back site during August. Lower rates during August, especially in the healthy area, were associated with low water levels which resulted in more oxidized sediments. The data reveal highly variable methanogenesis in the sediment which, when considered with sediment depths, indicates that sites of Phragmites die-back have significantly greater rates of anaerobic mineralization than surrounding healthy wetland, and may be intense sources of methane.
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  • 29
    ISSN: 1573-515X
    Keywords: autochthonous organic matter ; carbon dioxide ; decomposition ; methane ; nitrous oxide ; δ13C
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The vertical distribution of dissolved greenhouse gases (CH4,ΣCO2 and N2O), NO $${\text{NO}}_{\text{2}} - $$ ,and δ13C of ΣCO2 in Lake Biwa during a stagnantperiod was precisely determined. ΣCO2 as well as NO $${\text{NO}}_{\text{3}} - $$ was accumulated in the hypolimnion, whereas NO $${\text{NO}}_{\text{2}} - $$ and CH4concen\-trations were generally higher in theepilimnion than in the hypolimnion. In August, NO $${\text{NO}}_{\text{2}} - $$ andCH4 were ephemerally accumulated at the thermocline. Theconcentration of CH4 always exceeded equilibrium with respectto air/water exchange. N2O was rather uniformly distributed inboth time and space, and remained near equilibrium with respect toair/water exchange. All of these observations are similar to otherstratified, oligotrophic lakes, in which the hypolimnia were welloxygenated. The δ13C of ΣCO2 became morenegative with increasing depth, and showed a strong negativecorrelation with apparent oxygen utilization. From the data, the δ13Cvalue of organic matter decomposed into ΣCO2 inthe hypolimnion was calculated by isotope mass-balance, and found tobe in a similar range to δ13C of phytoplankton and benthic algaeand distinctively higher than δ13C of both terrestrial andsedimentary organic matters. This suggests that autochthonous organicmatter was the major source of ΣCO2.
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  • 30
    ISSN: 1573-515X
    Keywords: glucosidase ; methane ; peat ; phosphatase ; sulphate ; sulphatase ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Possible interactions between soil enzymes and thebiogeochemistry of wetlands were investigated duringa field-based drought simulation. Under control(waterlogged) conditions, correlations were foundbetween the activity of the enzyme B-glucosidase andtwo properties associated with carbon cycling, namelyi) CH4 release r = 0.79,p lt 0.01) and ii) dissolvedorganic carbon concentration (r= -0.81, p lt 0.01). In contrast,the transition to drought conditions resulted in correlations betweenB-glucosidase activity and certain mineralisationprocesses, namely the release of mg and Ca(r = 0.72, p lt 0.05). Sulphataseactivity correlated with changes in sulphate concentration during the droughtsimulation (r = 0.73, p lt 0.05).Further support for the suggested enzymic involvement in biogeochemicalprocesses was found in laboratory studies. Theseexperiments indicated that increasing the abundance ofB-glucosidase could stimulate trace gas emissions(p lt 0.001) and increase the concentration ofmagnesium and calcium (p lt 0.05). Increasedsulphatase abundance caused a suppression of methane emissions(p = 0.053).
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    Journal of atmospheric chemistry 23 (1996), S. 37-49 
    ISSN: 1573-0662
    Keywords: Ab initio ; methane ; chlorine ; kinetic isotope effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Recent studies suggest that the destruction of methane by Cl• in the marine boundary layer could be accounted for as another major sink besides the methane destruction by OH•. High level ab initio molecular orbital calculations have been carried out to study the CH4+Cl• reaction, the carbon Kinetic Isotope Effect (KIE) is calculated using Conventional Transition-State Theory (CTST) plus Wigner and Eckart semiclassical tunneling corrections. The calculated KIE is around 1.026 at 300 K and has a small temperature variation. This is by far the largest KIE among different processes involving atmospheric methane destruction (e.g., OH•, soil). A calculated mass balance of atmospheric methane including the KIE for the CH4+Cl• reaction is found to favor those methane budgets with enhanced biological methane sources, which have relatively lighter carbon isotope composition.
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    Biogeochemistry 34 (1996), S. 57-70 
    ISSN: 1573-515X
    Keywords: Cladium jamaicense ; Eleocharis spp. ; Typha domingensis ; interstitial water ; methane ; sulfate ; northern Belize
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Wetlands of northern Belize provide a unique opportunity to study methane production and emissions from marshes dominated by identical species (Typha domingensis, Cladium jamaicense) and genus (Eleocharis spp.), but differing substantially in the amount of sulfates present in the sediments. Some marshes occur on limestone marls rich in gypsum (CaSO4) while others are underlain by alluvial sands poor in sulfates. Concentrations of methane and sulfates in the sediment interstitial water are one or more orders of magnitude different for these two geological substrata averaging 139.2 and 14.9 μM of CH4, and 0.08 and 11.53 mM of SO4 −2 2 on alluvial sands and limestone respectively. The amount of methane found in the internal atmosphere of plants from alluvial sands is significantly higher (6.3 μM) than in plants from limestone (0.19 μM). The average methane emissions measured in wetlands located on alluvial sands were 25.2 mg m−2 h−1 while emissions from marshes on limestone were only 2.4 mg m−2 h−1. These values extrapolated for the entire year and the respective wetland areas resulted in the estimate of total CH4 emissions from northern Belize of 0.066 Tg per year.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 73-75 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
    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 20 (1996), S. 153-154 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 191-208 
    ISSN: 0363-9061
    Keywords: foundation design ; pavement design ; layer-stiffness technique ; moving strip load ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Analytical determination of stresses and deformations caused by moving loads is vital to foundation and pavement designs. In current applications, moving loads are often approximated to be vertical impact loads. In this work, however, a live load is modelled as a uniform distribution of normal or shear stresses in actual motion. Then, a layer stiffness approach utilizing linear elasticity is followed in determining the surface and interior deformations due to the live load. By superimposing the two solutions for normal and shear surface stresses, the new approach can be made to provide an approximate solution to the problem of evaluating stresses and deformations caused by a wide wheel load rolling on a layered elastic system. Although elastic solutions in general are inadequate to explain the more significant consequences of pore pressure generation and dissipation in the soil subgrade, these results can certainly be useful to examine the shearing effects of wide rolling wheels on the asphalt layer and immediate settlement of the subgrade. It is found that the dynamic effects of a smoothly rolling wide load are significant at relatively low wheel velocities compared to those of shear waves in the subgrade and base.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 143-152 
    ISSN: 0363-9061
    Keywords: settlement ; axially loaded ; circular ; piles ; piers ; drilled shafts ; caissons ; numerical model ; variational principles ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A variational model for the analysis of axially loaded piers is presented. A closed-form solution technique employing an iterative procedure, is developed to obtain the displacement and forces in the pier along its axial direction. The method is suitable for similar analyses of pile foundations. It is shown that displacements and the load distribution along the axis of the pier compare well with a more sophisticated finite element solution. Furthermore, the new model complements the well-known Reese model employing t-z curves for the analysis of settlement of axially loaded piers. This new formulation using continuum mechanics principles, distributes the work done by the applied load as compressive strain energy in the pier, and as shear strain energy in the soil, as well as, the compressive strain energy in the soil surrounding the pier and at the bottom of the pier.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 77-77 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 173-190 
    ISSN: 0363-9061
    Keywords: stress/stability analysis ; constitutive modelling ; non-linear fault behaviour ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A boundary element model for stress/stability analysis of underground excavations in the vicinity of faults is presented. The boundary element formulation adopts the fictitious stress method for the simulation of excavation boundaries and the displacement discontinuity method for the representation of faults. The numerical model employs the Barton-Bandis non-linear joint model for the modelling of the fault behaviour and linear elastic behaviour for the rock. An incremental-iterative in situ stress relaxation algorithm is implemented for the non-linear analysis of the faults. Both deformation and peak strength models of Barton-Bandis are incorporated for modelling the mechanical behaviour of the fault. The non-linear deformation of fault considers the effects of coupling between shear and normal stresses and displacement, joint closure, joint separation, hardening followed by post-peak or residual behaviour. The peak strength model employs a mobilized non-linear shear strength envelope. The differences between linear and non-linear simulation of the fault models are discussed. A comparison of model predictions with the classical Mohr-Coulomb peak strength model with constant joint stiffness is presented. The numerical model is used for a case study of Canadian hard rock underground mine. The shear and normal displacements along the fault during four mining sequences with backfill simulation are presented and discussed.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 229-230 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 253-273 
    ISSN: 0363-9061
    Keywords: elastic porous media ; wave propagation ; first-order silent boundary technique ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Wave propagation both in one- and in two-dimensional saturated elastic porous media is analysed by means of a two-field finite element model with silent boundaries. An extension of the elastic ‘multidirectional’ transmitting boundary to two-phase media is developed to simulate the silent boundary condition. The theoretical assessment and the numerical formulation of the first-order silent boundary technique is presented in detail. Some examples are used to demonstrate the reliability of the first-order method, especially for problems with plane and axisymmetric waves having various angles of incidence. Finally, the wave propagation along a pile shaft is presented, to simulate a common non-destructive dynamic pile test.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 287-294 
    ISSN: 0363-9061
    Keywords: torsional surface waves ; propagation ; hoterogeneous half-space ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The paper discusses the propagation of torsional surface wave in a homogeneous substratum over a half-space with linearly varying rigidity and density. The study reveals that under assumed conditions, a torsional surface wave propagates in the medium. The velocities of torsional surface waves have been calculated numerically and are presented in a number of graphs. It is also observed that for a stratum over a homogeneous half-space, the velocity of torsional surface waves coincides with that of Love waves. For a non-homogeneous half-space it is observed that the velocity of torsional surface waves is always higher than that of Love waves propagated in a homogeneous layer over a homogeneous half-space. An attempt is also made to assess the possible propagation of torsional surface waves in a half-space with linearly varying rigidity and density, lacking a superficial layer. It is concluded that such a half-space allows two solutions for torsional waves while a homogeneous half-space has one.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 381-401 
    ISSN: 0363-9061
    Keywords: Poroelasticity ; FEM ; borehole ; anisotropy ; rock mechanics ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The finite element equations for non-linear, anisotropic poroelasticity are cast in the form of measurable engineering constants. Two problems of importance to the rock and petroleum industry are analysed by the FEM. First, the classical Mandel's problem with an extension to transversely isotropic case is investigated. Second, the problem of an inclined borehole is explored. In particular, the effect of material anisotropy on stress concentration near the wall with implication to borehole instability is examined in detail.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 489-516 
    ISSN: 0363-9061
    Keywords: cavity expansion ; critical state models ; plasticity ; pile installation ; normally and overconsolidated clays ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Boundary value problems for hardening/softening soils, such as Cam-Clay, usually require the extensive use of finite element methods. Here analytical and semi-analytical solutions for the undrained expansion of cylindrical and spherical cavities in critical state soils are presented. The strain is finite, the initial cavity radius is arbitrary and the procedure applicable to any isotropically hardening materials. In all cases only simple quadratures are involved, and in the case of the original Cam-Clay a complete analytical solution can be found. In addition to providing models of the behaviour of displacement piles and pressuremeters these results also provide valuable benchmark solutions for verifying various numerical methods.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 595-604 
    ISSN: 0363-9061
    Keywords: compressibility ; elastic settlement ; geosynthetic-reinforced soil ; mechanical foundation model ; prestressing ; Engineering ; Engineering General
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    Notes: In the present paper, a new foundation model has been proposed by introducing a stretched rough elastic membrane in the Pasternak shear layer sandwiched between two spring layers which is an extension of Kerr model. Considering the equilibrium of different elements, the equations governing the elastic settlement response of the model are derived. Finite difference scheme has been employed to solve the governing equations. The parametric studies carried out show the effect of several parameters on the elastic settlement response of the model. The proposed model is well suited for idealizing the behavior of geosynthetic-reinforced granular fill - soft soil system besides other applications.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 571-593 
    ISSN: 0363-9061
    Keywords: methane gas ; finite element ; coal mining ; diffusion ; adsorption ; outbursts ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: This paper presents the development of a mathematical model for methane gas migration in coal seams. The major focus of this model is the coupling between the gas flow and deformation of solid coal. The effect of diffusion of adsorbed methane gas from the solid matrix to the voids has been taken into account. The adsorption of gas in the coal seam causes a two-phase state of gas flow. The governing equation for the two-phase gas flow is a non-linear partial differential equation with non-linear boundary conditions. A finite element model has been developed for simulation of the distribution of pressure and concentration of methane gas due to gas migration in coal seams.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 673-690 
    ISSN: 0363-9061
    Keywords: tunnel analysis ; new implicit method (NIM) ; Engineering ; Engineering General
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    Notes: Tunnel excavation is a coupled three-dimensional problem dealing with two different structures: lining and rockmass. For a simple application it is useful to develop simplified methods by treating the problem as plane strain.If the problem of tunnel face advance presents an axisymmetric geometry, then we show that the major parameter governing the ground-interface-lining interaction is the convergence of the tunnel U0 at the moment of the lining installation.The ‘New Implicit Method’ (NIM) presented in this paper makes use of principles similar to those of the ‘convergence-confinement’ method, but it provides a better appreciation of the coupled behaviour of rockmass and lining. For independent time constitutive laws (elasticity and plasticity), we point out that the convergence U0 depends not only on the mechanical behaviour of the rockmass and on the distance from the tunnel face, as predicted by the ‘convergence-confinement’ method, but also on the stiffness of the lining previously set.We present the ‘NIM’ for elastic and perfect elastoplastic rockmasses without dilatancy for many criteria. The development of this new method is based on the results of tunnel calculations with an axisymmetric FEM numerical model that takes into account the three-dimensional aspect of the problem.Using this method is simple and its results agree well with the FEM numerical results. Its accuracy is highly satisfactory for a geotechnical study.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 693-713 
    ISSN: 0363-9061
    Keywords: unfrozen layer ; osmotic ; diffusion ; transport ; moisture ; temperature ; optimization ; Engineering ; Engineering General
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    Notes: Two series of freezing column tests with distilled water and municipal solid waste leachate were investigated, using illitic silty clay. Temperature distributions along the freezing column were recorded as a function of distance and time. Unfrozen moisture content and osmotic pressures as a function of temperature were calculated.It was shown that temperature distributions as a function of distance and time were similar in all tests, probably as a result of the limited amount of moisture intake. The amount of moisture intake was directly related to freezing time and temperature gradient in the freezing column. Unfrozen moisture contents, ion concentrations and temperature gradients were identified as the controlling parameters that contributed to the boundary layer transport (BLT) of metal ions in frozen specimens. Na+ concentration profiles were mostly dependent on water movement in the freezing column. The behaviour of Ca2+ and Mg2+ cations was similar to Na+; their concentrations in the soil solution decreased with freezing time due to ion exchange.Temperature, moisture content in an unfrozen boundary layer (UBL), and concentration gradient were taken into consideration in the development of a boundary layer transport model (BLTM). Based on the experimental results and Powell's optimization technique, the diffusivity parameters of various metal ions were calculated. Comparison of experimental and predicted results indicated that the BLTM can predict the migration of metal ions in UBL.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 725-751 
    ISSN: 0363-9061
    Keywords: damage mechanics ; earthquakes ; gravity dam ; damage evolution ; absorbing boundary ; anisotropic behaviour ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: In this paper, the seismic response analysis of concrete gravity dams is presented using the concept of Continuum Damage Mechanics. The analysis is performed using the finite element technique and a proper material degradation/damage model. The damage criterion used here is a second order tensor model based on elastic-brittle characterization and on a power function of the principal tensile stress. The methodology employed is shown to be computationally efficient and consistent in its treatment of both damage growth and propagation. Other important features considered in the analysis are: (1) dam-foundation interaction (2) appropriate modelling of joined rock mass using continuum damage mechanics, and (3) proper modelling of unbounded domain of foundation rock. The infinite media representation of the foundation material has been achieved by using doubly asymptotic approximation. The results of the analysis indicate that the seismic response of a damaged concrete dam could be significantly different from that of an undamaged one. In particular, the analysis shows that during a seismic event, the microstructure of a damaged zone can significantly change due to growth and propagation of microcracks.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 831-844 
    ISSN: 0363-9061
    Keywords: double porosity ; consolidation ; fissured material ; coupled problems ; Engineering ; Engineering General
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    Notes: The mathematical base of the double porosity concept, consisting of the continuity and equilibrium equation respectively, is briefly reviewed. A quasi-steady-state transfer function, the so-called leakage term, is used. Important aspects of the developed code, based on the double porosity theory, are presented together with two hypothetical example problems. The resulting trend of the settlements are compared to those from previous work and was found to be significantly different. However, the implications are that the present study exhibits a more realistic prediction for the settlement.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 907-908 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
    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 20 (1996), S. 887-905 
    ISSN: 0363-9061
    Keywords: creep ; modelling ; long-term ; triaxial ; drainage ; marine clay ; Engineering ; Engineering General
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    Notes: A new finite element program is introduced and its predictive capabilities are compared to results from two long-term, drained laboratory creep tests on a deep sea clay. The constitutive behaviour is based on Cam clay critical state plasticity theory with creep and time-dependent hardening. Creep is computed using either Singh-Mitchell's three-dimensional equation or Taylor's secondary compression relationship. The experimental creep data include a triaxial specimen subjected to two deviatoric stress increments and a one-dimensional consolidation specimen subjected to three vertical stress increments. In addition, the pore pressure behaviour following an increase in stress is examined in the triaxial sample. Predictions compare favourably to test data, which provide confidence for applying the chosen constitutive model and numerical formulation to solve seabed-related problems on the continental slope that are of interest to geologists, the oil industry and the navy, among others.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 517-544 
    ISSN: 0363-9061
    Keywords: rock reinforcement ; load distribution ; cable bolts ; fully grouted ; Engineering ; Engineering General
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    Notes: Explanation for the widely reported observation that fully grouted reinforcement is more effective in hard rock that behaves as a discontinuum than in soft rock is presented. Analytical solutions are presented for the distribution of displacement and load along an untensioned fully grouted elastic bolt, of specified bond stiffness, which is activated during excavation by either a continuous or discontinuous distribution of rock displacement. The results indicate that significantly higher axial loads are developed for the discontinuous case.Since the mechanics of bond failure depend on the type of bolt and grout used, in the second part of the paper a finite difference formulation is introduced and combined with a non-linear model for the bond behaviour of a cement grouted seven-wire strand cable bolt. The results of a parametric study indicate that, because the bond is frictional and depends on confinement at the borehole wall, for the same profile of rock mass displacement lower loads are developed in soft rock. Furthermore, in soft rock, excavation induced stress changes can cause a dramatic reduction in bond strength, so that, even after significant rock mass displacement, the axial load developed is significantly less than the tensile strength of the cable. A combination of these effects can explain why failures of cable bolted ground involve debonding at the cable-grout interface in soft rock, and why instances of cable rupture are confined to hard, blocky rock masses.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 647-671 
    ISSN: 0363-9061
    Keywords: tailings ; consolidation ; evaporation ; salinity ; numerical modelling ; Engineering ; Engineering General
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    Notes: Large-strain consolidation theory has been used as the basis of a computer program for dealing with the problem of consolidation of slurried tailings. The work was carried out in the context of the gold-mining industry in Western Australia, where net annual evaporation rates are high (from about 3 to more than 4m/yr). Therefore, a simple, but effective, method of dealing with evaporation has been included in the model. The paper describes the model, and then uses it with some typical problems to illustrate its versatility and to show the complexity of the behaviour which can occur.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 691-692 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. ii 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 79-99 
    ISSN: 0363-9061
    Keywords: Land displacement ; groundwater pumping ; Galerkin finite element model ; Engineering ; Engineering General
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    Notes: Equations of equilibrium (force balance) and flow in multidimensions were coupled in this paper to describe land displacements due to pressure decline in aquifers. A Galerkin finite element model based on these equations was developed. The saturated/unsaturated behaviour and the isotropic/anisotropic properties of permeability and elasticity were considered when the model was formulated. This model was verified by comparing its simulation results with those of known analytical solutions for simplified cases. The simulation of displacements due to pressure decline in unsaturated media was also performed. Those results demonstrated that the choice of boundary ranges for an aquifer with infinite domain may significantly affect the estimated horizontal and vertical displacements. To obtain a good estimation of land displacements, the boundary ranges should be carefully chosen. The displacements occurring in unconfined aquifers are caused by the drop of the water table and the change in body force in the dewatering zone. Simulation results also indicated that the change in body force should be considered once an unconfined aquifer has been pumped. Otherwise, the horizontal and vertical displacements in unconfined aquifers would be overestimated and underestimated, respectively. The behaviour of land displacements due to pumping was shown to be affected by changes in the total stresses in aquifers.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 57-72 
    ISSN: 0363-9061
    Keywords: piled raft systems ; raft-pile-soil interaction ; finite layer methods ; foundations ; Engineering ; Engineering General
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    Notes: This paper presents a method of analysis for piled raft systems constructed in layered soils. The method presented takes account of the interactions of the raft, piles and soil without the cost of a full three-dimensional rigorous analysis. This is done by the use of finite layer methods for the analysis of the soil and finite element methods for the raft. Examples are provided in the paper for piled rafts constructed on layered soils, and results are presented for bending moments in the raft and loads in the piles.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 1-33 
    ISSN: 0363-9061
    Keywords: interface constitutive model ; deformation behaviour ; spherical asperity interaction ; dual asperity interaction ; shear and dilatancy of joints ; Engineering ; Engineering General
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    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: An interface constitutive model is presented accounting for slip and sliding effects and also for dilatancy phenomena. The microslip effects are described by considering spherical asperity interaction with variation of contact area and generation of progressive or reverse slip zones. The incremental constitutive equations are derived with proper memory rules accounting for generation and annihilation of particular slip zones during the process of variable loading. It is further assumed that sliding of spherical contacts occurs along large asperities whose slope varies due to the wear process. The predicted shear and dilatancy curves are shown to provide close quantitative simulation of available experimental data. The strain ratchetting effect for non-symmetric cyclic loading was exhibited using the asperity wear model. The model presented could be applied to simulate rock joints, masonry, or concrete cracked interfaces, under monotonic and cyclic loading.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 155-171 
    ISSN: 0363-9061
    Keywords: pollutant migration ; solute breakthrough curves ; numerical simulation ; porous media ; Engineering ; Engineering General
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    Notes: The effect of heterogeneity on solute transport in porous media is examined by means of physical experiments and controlled numerical simulations. The special cases of layered, clogged and aggregated porous media are particularly investigated. The breakthrough curves (BTCs) obtained from some sections of the physical models are extremely distorted with extended concentration tails. These tailings are caused by different trajectories of the tracer through fine (millimeter and centimeter) scale spatial heterogeneities. On the other hand, BTCs in sections of the physical models having no heterogeneous nature, showed classical ‘S’-shape.A computer simulation based on an improved capacitance model was used to match the experimental data. The BTCs can be represented adequately by the model. However, it seems necessary to determine the fitting parameters experimentally in order to relate them to actual physical phenomena.
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 275-285 
    ISSN: 0363-9061
    Keywords: elasticity ; stress analysis ; inclusion ; interface ; sand ; Engineering ; Engineering General
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    Notes: In this paper, the stress states of a sand particle (or aggregate) with an interface layer in a cement paste (or mortar) subjected to uniaxial compression or tension are studied. This is a dual layer inclusion problem. The general analytical solutions of stresses and deformations are obtained in closed form, and the solutions of several special cases including the sand (or aggregate) treated as rigid body and as a hole as well as when the thickness of the interface layer approaches zero are also given.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 295-302 
    ISSN: 0363-9061
    Keywords: cubic-strain quadrilateral ; predicting collapse-loads ; Engineering ; Engineering General
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    Notes: In this paper, a fourth-order displacement (cubic strain) Serendipity quadrilateral element is presented. The shape functions and integration scheme are introduced, followed by a series of convergence tests, indicating that the element does not have any spurious zero-energy modes, and passes the patch test and single-element tests. Modifications are then made to enable the element's use in effective stress analysis problems. Examples are finally solved using the element and a comparison is made between some computed and closed-form solutions. It is also shown that the cubic strain quadrilateral may be used in conjunction with or as a substitute for the cubic strain triangle when predicting collapse loads for undrained plane or axisymmetric problems in the fully plastic range.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 331-349 
    ISSN: 0363-9061
    Keywords: elasticity ; buried pipes ; surface heading ; soil-structure interaction ; Engineering ; Engineering General
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    Notes: A method is presented which may be used to compute the displacements, strains and moments (both in-plane and transverse) in buried structures such as pipelines and culverts subjected to longitudinal bending. This type of bending can occur if a surface loading such as a vehicular loading or an embankment loading is applied to the soil above the pipe or culvert.Fourier transforms are used to reduce the three-dimensional problem to one involving only two spatial directions, thereby reducing the data preparation and computation time. Conventional finite element analysis is used to approximate the field quantities in the transformed two-dimensional plane. Two Fourier integral element types have been developed which have many applications in geotechnical engineering.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 443-452 
    ISSN: 0363-9061
    Keywords: heat-fluid-stress diffusion ; Gauss-Legendre ; Laplace transform ; Stehfest method ; Engineering ; Engineering General
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    Notes: Three methods (Gauss-Legendre method, Stehfest method and Laplace transform method) are used to evaluate a solution of a coupled heat-fluid linear diffusion equation. Comparing with the results by Jaeger, the accuracy and efficiency of the Stehfest and Gauss-Legendre methods and the limitations of the truncated solutions obtained by Laplace transformation are discussed. It is concluded that the Stehfest method gives accurate results and is numerically more efficient than the other two methods, particularly for the solutions in early time. Two transformations with u=-ln(x) and u=arctan(xπ/2), where u is the original integral variable, are considered in the Gauss-Legendre method.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 431-442 
    ISSN: 0363-9061
    Keywords: foundations ; rigid pier ; moment carrying capacity ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Numerical predictions of the immediate moment carrying capacity of a short pier foundation in saturated clay are presented. Three-dimensional finite element analyses are carried out using linear and non-linear programs and using a linear axi-symmetric program.Preliminary investigations are made to determine suitable boundary distances for analysis at full-scale and size of loading increment for non-linear analyses.Predictions of the behaviour of prototype pier and of conventional and centrifuge models of this pier are then made. It is shown that the axi-symmetric program yields significantly higher rotations per unit moment than the linear three-dimensional program and that, using both of these programs, elastic analyses of the conventional and centrifuge models and of the prototype yield very similar results. It is also shown that non-linear analyses of the conventional and centrifuge models yield significantly different moment/rotation relationship in accordance with the behaviour actually observed in the model tests. The relationship obtained for the centrifuge model is shown to differ only slightly from that obtained for the prototype, due to the boundary restrictions in the model, and to be of the same order as the centrifuge test result at working condition but not at ultimate capacity.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 545-546 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. ii 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 865-886 
    ISSN: 0363-9061
    Keywords: finite element method ; large deformation ; cone penetration test ; layered soil ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: An Eulerean large-strain finite element formulation is presented to simulate static soil penetration. The method is an extension of the Updated Lagrangean description to an Eulerean formulation taking into account convection of deformation-history-dependent properties as well as material properties. The strength of the soil is characterized by a non-associated Drucker-Prager criterion which depends on peak and critical friction angles. The model is applied to cone penetration in two-layer systems: (a) clay on sand and (b) sand on clay.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 635-646 
    ISSN: 0363-9061
    Keywords: slope stabilization ; piles ; soil response modelling ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Piles used for the stabilization of slopes have to be adequately designed to resist the induced lateral loads due to the movement of the unstable slope. In this paper, a numerical method is presented for the analysis of this problem. In this approach, the piles are modelled using beam finite elements. The soil response at the individual piles is modelled using the modulus of subgrade reaction and pile-soil-pile interaction considered using the theory of elasticity. Two case histories, one for single pile and the other for pile group, are analysed which show that the numerical model can predict the general characteristics of the piles reasonably well. The study suggests that the design of the piles based on the computed response from single pile analysis, ignoring group effects, may be unduly conservative.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 753-767 
    ISSN: 0363-9061
    Keywords: dynamic ; compaction ; soil ; damping ; non-linear stressing ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The majority of currently available analytical tools to predict ground stresses due to impact are based on linear spring-dashpot dynamic models. Although these simple models adequately represent stiff ground possessing linear visco-elastic behaviour, they suffer from two striking limitations when applied to relatively softer ground; (1) the inability to account for the permanent deformation resulting from impact, (2) failure to incorporate stiffness changes of softer soil within the impact duration. In this paper, the authors present an improved analytical approach formulated on the basis of a series of laboratory impact tests, to address the shortcomings of the current dynamic models in relation to soft soils. In this procedure, the impact zone is modelled as three distinct zones; (1) a zone beneath the falling weight undergoing non-linear axial deformation while being in vertical motion, (2) an inner zone immediately surrounding zone 1 with non-linear shear deformation, and (3) an outer zone undergoing a relatively lower degree of (linear) shear deformation. The soil constitutive parameters pertinent to the model are obtained from a modified dynamic compression test that simulates the impact conditions. It is shown that analytical predictions of the impact stress history and penetration are in agreement with test results. The findings are useful in the exploration of dynamic compaction techniques that will be effective in soft soil improvement.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 845-846 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996) 
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    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 231-252 
    ISSN: 0363-9061
    Keywords: interfaces and joints ; landslides ; viscoplastic behavior ; hierarchical single surface models ; laboratory testing ; calibration ; finite element method ; validations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A constitutive model to describe viscoplastic or time-dependent behaviour of interface materials is presented. Viscoplastic characteristics of the interface material are modeled based on Perzyna's theory of viscoplasticity and the Hierarchical Single Surface (HiSS) series of constitutive models. Experiments performed using a new interface test device to characterize the behaviour of cohesive soil-rock interfaces are described. Procedures to derive model parameters are presented together with validation of the model. Finite element implementation of the interface element is described along with verification of the model with respect to field behaviour of a creeping natural slope.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 365-375 
    ISSN: 0363-9061
    Keywords: Rayleigh waves ; propagation ; heterogeneous incompressible substratum ; homogeneous incompressible half-space ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The paper studies the propagation of Rayleigh waves in an incompressible layer with general variation of rigidity as μ=μ0(1+bz)m resting over a homogeneous incompressible elastic half-space. Instead of using the Whittaker function, the expansion formula proposed by Newlands has been used for better results at shallow depths. As a particular case for m=1, the results have been shown to coincide with those obtained by Newlands. The velocities have been computed for different values of m and the results are presented in graphs.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 351-364 
    ISSN: 0363-9061
    Keywords: elastic non-homogeneity ; circular foundation ; elastic indentation ; integral equations ; weathered crust ; contact problem ; surface non-homogeneity ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The present paper examines the elastostatic problem pertaining to the axisymmetric loading of a rigid circular foundation resting on the surface of a non-homogeneous elastic half-space. The non-homogeneity corresponds to a depth variation in the linear elastic shear modulus according to the exponential form G(z)=G1+G2e-ζz. The equations of elasticity governing this type of non-homogeneity are solved by employing a Hankel transform technique. The mixed boundary value problem associated with the indentation of the half-space by the rigid circular foundation is reduced to a Fredholm integral equation which is solved via a numerical technique. The numerical results presented in the paper illustrate the influence of the near-surface elastic non-homogeneity on the settlement of the foundation.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 403-430 
    ISSN: 0363-9061
    Keywords: swelling ; chemo-poroelasticity ; borehole stability ; osmosis ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Water-absorbing rocks are formed from minerals that can hold water in their crystal structure or between grain boundaries. Such water absorption is often accompanied by a change in the crystal dimension that manifests itself as a swelling of the rock. Swelling is particularly pronounced in rocks containing phyllosilicates because of the ease with which these minerals hydrate; it is thus of geological and geotechnical relevance in shales, clay-rich soils and zeolitized tuffs. The model of hydration swelling that we present here is based on extended versions of the equations of poroelasticity and Darcy's transport law, which we derive using a non-equilibrium thermodynamics approach. Our equations account for the hydration reaction under the assumption that the reaction rate is fast in comparison with the rate at which hydraulic state changes are communicated through the rock, i.e. that local physico-chemical equilibrium persists. Using a finite-element scheme for solving numerically the governing equations of our model, we simulate the creep of shales during a routine swelling test and calculate the stress and strain distributions around wellbores drilled in shale formations that undergo swelling. We show that swelling effects promote tensile failure of the wellbore wall.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 303-304 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
    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 20 (1996) 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 771-783 
    ISSN: 0363-9061
    Keywords: localization ; regularization ; discontinuity ; plasticity ; mohr-Coulomb ; ductile fracture ; Engineering ; Engineering General
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    Notes: A frictional material model is investigated with respect to the existence and development of a regularized strong discontinuity within the constitutive framework of plasticity theory. It appears that the condition for the existence of such a discontinuity is identical to the classical bifurcation criterion for band shaped bifurcation in the rate of deformation field. The model behaviour is also discussed beyond onset of localization, for a band with fixed orientation, where the state variables are allowed to change.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 815-830 
    ISSN: 0363-9061
    Keywords: groundwater ; velocity ; heat transquent ; heated cylinder ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: An isothermally heated, impervious cylinder, which is placed normal to the path of flowing groundwater, is theoretically evaluated for its potential to serve as a kind of ‘groundwater velocimeter’. The essential task is to determine whether the variation in heat output along the cylinder perimeter is sufficiently large to permit measurement for typical groundwater velocities. Using finite elements, the governing equations of advective thermal transport in saturated porous media are solved to obtain the variation in heat output along the circumference of the heated cylinder. An annular region of different hydraulic conductivity is assumed to separate the cylinder from the surrounding formation. The creation of such a region during placement of a cylinder is inevitable. A parametric study led to the following conclusions: (1) A smaller cylinder radius is preferable since the time to achieve a particular degree of asymmetry in heat output is then greatly reduced. (2) An annular region of lower hydraulic conductivity, relative to formation, reduces output asymmetry by no more than 25%, but if hydraulic conductivity is increased, output asymmetry can increase several times. (3) For annular regions having a higher hydraulic conductivity than the surrounding formation, annular thickness is not important. (4) The least groundwater speed which may be accurately measured by such a device will depend heavily upon instrumentation but is tentatively placed at about 5⋅0×10-5 cm/s. Theoretical results are approximately confirmed by preliminary experiments with a prototype device which has been constructed so as to directly measure the expected variation in thermal output. Partial construction details are provided.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 847-864 
    ISSN: 0363-9061
    Keywords: finite element-method ; contaminant migration ; fractured porous media ; mass transport ; double-porosity model ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper describes the development of a finite element method for analysing contaminant transport in double-porosity geomaterials using a time-stepping approach. In many cases, double-porosity models may be used to represent fractured rock formations and fissured soils. A distinctive feature of utilizing this kind of model is that it is not necessary to have an intimate knowledge of the nature, distribution and properties of individual fractures and fracture arrangement since the fracture geometry and details are considered only in an averaged or equivalent continuum sense. The flux exchange that occurs between the fluid in the fractures and in the solid matrix is represented by a linear heriditary process. This has the consequence that in order to carry the solution forward from time t to t+Δt, it is necessary to know and to store the complete contaminant history up to time t. This paper shows that all the hereditary information necessary to carry the solution forward is contained in the values of certain hereditary variables at time t so that it is not necessary to store the complete time history and consequently a more efficient numerical process can be developed.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 35-56 
    ISSN: 0363-9061
    Keywords: waste containment systems ; slope failure ; strain-softening ; landfill ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The potential for progressive failure in waste containment systems is an important design consideration. Many common interfaces between components in containment systems exhibit strain-softening behaviour; however, slopes are presently designed using limit equilibrium methods that do not account for these effects. An analytical model is developed to investigate the potential for progressive failure due to strain softening. Results are presented in a non-dimensional form relating the potential for strain softening to the slope geometry, the waste properties and the properties of the containment system interface. The potential for progressive failure increases as (i) the waste stiffness decreases relative to the initial stiffness of the interface resistance, (ii) the length of the slip surface increases and (iii) the rate of strain softening with displacement increases. Analysis of a case study slope failure indicates that the analytical approach produces results that are consistent with field observations and comparable to results from a more sophisticated, numerical analysis. Although simple, this analytical approach serves as a useful design guide to identify cases where it is unsafe to use the peak shear strength in a limit equilibrium analysis.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 101-117 
    ISSN: 0363-9061
    Keywords: dynamic photoelasticity ; stress waves ; WAVE ; stress wave modelling ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Dynamic photoelasticity is used as a means for visualizing the complex interaction process between elastic waves and geometrical discontinuities. The photoelastic experiments are back-analysed by the dynamic finite difference program WAVE, and the code is assessed in terms of its accuracy and modelling capabilities. Three model geometries are investigated: (i) a stope situated within a homogeneous medium; (ii) a stope surrounded by softened material, the interface between the softened and bulk material being bonded and (iii) a stope situated within softened material, with a non-cohesive material interface. Prominent waves resulting from the diffraction, refraction and reflection of incident waves, as well as normalized dynamic stress intensification factors at the stope face, stope back area and along the hanging-wall skin are analysed in this study.The parting planes are found to reflect a portion of the incident energy and thus shield the stope. However, a non-cohesive parting plane traps energy within the hanging-wall beam, and any shielding benefits are negated. WAVE has been proven to model accurately the diffraction, refraction and reflection of stress waves in a homogeneous medium and the interaction with cohesive and non-cohesive interfaces separating two material types.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 119-141 
    ISSN: 0363-9061
    Keywords: inverse analysis ; parameter identification ; underground excavation ; optimization technique ; finite element method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A probabilistic framework to perform inverse analysis of geotechnical problems is presented. The formulation allows the incorporation of existing prior information on the parameters in a consistent way. The method is based on the maximum likelihood approach that allows a straightforward introduction of the error structure of field measurements and prior information. The difficulty of ascribing definite values to the uncertainties associated with the various types of observations is overcome by including the corresponding variances in the set of parameters to be identified. The inverse analysis results in a minimization problem that is solved by coupling the optimization technique to the finite element method. Two examples are presented to illustrate the performance of the method. The first one corresponds to a synthetic case simulating the excavation of a tunnel. Young's modulus, K0 value and measurements variances are identified. The second case concerns the excavation of a large underground cavern in which again Young's modulus and K0 are identified. It is shown that introduction of prior information permits the estimation of parameters more consistent with all available informations that include not only monitored displacements but also results from in situ tests carried out during the site investigation stage.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 209-213 
    ISSN: 0363-9061
    Keywords: torsional surface waves ; geophysical prospecting ; earthquake damage ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: It is well known that an elastic homogeneous half-space does not allow torsional surface waves to propagate. The present paper attempts to find out the possibility of propagation of such waves in a viscoelastic half-space. The study reveals that although the homogeneous elastic half-space does not allow torsional surface waves to propagate, a viscoelastic half-space does so. The wave is damped due to the viscoelastic parameter. It has also been found that as the viscoelastic parameter decreases, the medium becomes elastic and the torsional surface waves ceases to propagate.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 215-228 
    ISSN: 0363-9061
    Keywords: concrete ; interface layer ; microstructure ; mortar ; stress ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: In this paper, the influence of geometrical and physical parameters (size of the sand particle, thickness of the interface layer and ratios of the modulus of elasticity) on stress distributions in a mortar is studied. It is found that a weak or soft interface layer in the mortar will greatly reduce the strength of the concrete; if the modulus of the interface layer approaches to that of the cement paste and the modulus of the sand particle (or aggregate) is 4-10 times as large as that of the cement paste, the concrete will possess a much higher strength and thus has a better property.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 305-306 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 307-329 
    ISSN: 0363-9061
    Keywords: absorbing boundary ; liquefaction ; saturated soil ; soil-structure interaction ; 3-D strain space multimechanism ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A non-linear seismic response analysis method for 2-D saturated soil-structure system with an absorbing boundary is presented. According to the 3-D strain space multimechanism model for the cyclic mobility of sandy soil, a constitutive expression for the plane strain condition is first given. Next, based on Biot's two-phase mixture theory, the finite element equations of motion for a saturated soil-structure system with an absorbing boundary during earthquake loadings are derived. A simulation of the shaking table test is performed by applying the proposed constitutive model. The effectiveness of the absorbing boundary is examined for the 2-D non-linear finite element models subjected to random inputs. Finally, a numerical seismic response analysis for a typical saturated soil-structure system is performed as an application of the proposed method.
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 377-379 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 453-455 
    ISSN: 0363-9061
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical and Analytical Methods in Geomechanics 20 (1996), S. 457-488 
    ISSN: 0363-9061
    Keywords: Linear thermo-poro-elastic materials ; boundary element method ; Green's functions ; Dirac delta functions ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper presents a direct boundary element method of numerical analysis, formulated in the Laplace transform domain, for a plane strain analysis of a linear thermo-poro-elastic material consolidating in the presence of a heat source. The equations governing the behaviour of the material are assumed to be a set of self-adjoint and fully coupled linear equations. A physical intepretation of the constants appearing in the linear theory relevant to engineering applications is presented. A boundary integral equation is developed from the governing equations in a straightforward way using the properties of Dirac delta functions, and an approximate boundary element method of numerical analysis is implemented using the Green's functions derived previously by the authors. The numerical analysis presented is motivated by the engineering design of a heat generating radioactive waste repository located deep underground. For this reason, there is a description of the application of the boundary integral equation method presented to the numerical solution of several problems of theoretical and practical interest in the area of radioactive waste disposal in clay-like soils.
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