ALBERT

Description: Initiation and cessation of growth and total height of seedlings at ages 2 and 3 years were measured in a nursery experiment with 100 seed sources of Piceamariana (Mill.) B.S.P. from natural stands sampled across the range from the Atlantic Coast to Alaska. Correlations with climatic and geographic factors were calculated and principal component, variance, and regression analyses made. The results showed that photoperiod and temperature were major factors of natural selection and that a clinal variation pattern is predominant. Since south–north trends of photoperiod and temperature are closely related to latitude, the regression of phenological variables and of height on latitude of origin gave an indication of response gradients. Total height changed by 2 to 11% from the experimental mean if a seed source was moved 1° of latitude north or south from its native area to a new site. The consequences for seed movement and breeding programs are discussed.

Description: not available

Description: The shear strength of an unsaturated soil is written in terms of two independent stress state variables. One form of the shear strength equation is[Formula: see text]The transition from a saturated soil to an unsaturated soil is readily visible. A second form of the shear strength equation is[Formula: see text]Here the independent roles of changes in total stress σ and changes in pore-water pressure uw are easily visualized.Published research literature provides limited data. However, the data substantiate that the shear strength can be described by a planar surface of the forms proposed. A procedure is also outlined to evaluate the pertinent shear strength parameters from laboratory test results.

Description: Volume change constitutive relations for unsaturated soils are proposed from a semi-empirical standpoint. One equation describes the deformation of the soil structure and a second equation defines the volume of water present in the element. Each equation can be viewed as a three-dimensional surface with two independent stress state variables forming the abscissas.Uniqueness is tested by measuring volume changes resulting from stress changes in two orthogonal directions and comparing predicted and measured volume changes resulting from a stress change in a third direction. Samples of undisturbed Regina Clay and compacted kaolin showed good agreement between the predicted and measured volume changes for monotonic deformation of the soil structure. The agreement was not as close for the water phase. The variation was attributed to difficulties in measuring water volume changes over a long period of time. The laboratory results indicate that the proposed constitutive equations are of the appropriate form for use in engineering practice.

Description: It is common for the rate of seepage through a tailings embankment to be estimated on the basis of a conventional flow net analysis assuming steady seepage conditions. Moreover an impervious seal is generally recommended against the upstream face of the dam to minimize seepage flow through the sand embankment. This study shows that, due to rapid rates of placing, slimes can exist in an under-consolidated state. Field measurements are cited in support of the theory and the implications of under-consolidated slimes in the pond are discussed in detail. Procedures to analyse the utility of an upstream seal are also discussed and design examples reflecting actual operating conditions are given.

Description: Tailings dams differ from conventional earthfill structures in that much more time is available to optimize design since their construction is extended over a longer period. Laboratory data are presented on a variety of tailings sands which indicate that they are relatively strong and incompressible. Poor performance is likely to result from inadequate seepage control and instability due to liquefaction. In order to take advantage of opportunities for ongoing design, in situ permeability and density monitoring is needed together with pore pressure measurements. An infiltration test for the determination of permeability above the water table is proposed. In situ density determinations are made by driving a nuclear probe into the sands. The latter technique offers considerable promise for evaluating liquefaction potential of natural and fill deposits. Field experience is used to illustrate the application of the techniques.

Description: A study to observe the effects of overburden pressure and other parameters on the freezing behavior of a saturated soil was undertaken. A linear relationship between effective overburden pressure and the flow of water into or out of a freezing soil was observed. The effective pressure at which no flow occurred was termed the shutoff pressure. At pressures less than the shutoff pressure water was sucked to the freezing front resulting in segregated ice, ice lensing, and heaving. This heaving could significantly exceed the heave due to the volumetric expansion of the in situ porewater. At pressures greater than the shutoff pressure water was expelled from the freezing front thereby reducing the volume of in situ water and resulting in a relatively small amount of heave. Shutoff pressure was observed to depend on soil type, stress history, and freezing temperature. The effects of overburden pressure upon flow of water in a freezing soil and frost heave were recommended as additional criteria for assessing soil frost susceptibility.

Description: The data collected at a warm-oil test pipeline at Inuvik. N.W.T. are analyzed making use of the theory of thaw–consolidation proposed by Morgenstern and Nixon. The observed pore pressures, settlements, and rate of melting in the thawing permafrost foundation have been compared with their corresponding theoretical predictions. Bearing in mind the natural variability of ice-rich permafrost deposits, the agreement between prediction and observation is extremely encouraging. As the data collected at this test facility form the only completely documented case history of a thawing foundation in permafrost published to date, this comparison between theory and actual performance is valuable in establishing a level of confidence in the application of the theory of thaw–consolidation.

Description: Previously published data are inadequate to explain the high natural shear strength of oil sand. Dissolved gas comes out of solution when confining stresses are removed rapidly, and this results in an internal pressure that expands the oil sand specimens disrupting their fabric. Geophysical logs indicate that in situ densities are much higher than those determined from conventionally cored specimens.Although the behavior of slopes in oil sands suggests that the shear strength is high, the source of strength of the oil sand has not been explained. Therefore detailed oil sand strength testing was undertaken on samples obtained in a special manner. Down-hole refrigeration of cored sections resulted in relatively high-quality specimens, and these were shaped on a lathe to provide triaxial and shear-box test samples.Strength tests on dense Ottawa sand, oil sand tailings and densely recompacted oil sand were performed: standard behavior was observed throughout. A series of triaxial and shear-box tests on undisturbed oil sands demonstrated a Mohr failure envelope that is highly curved, which displays no cohesion intercept and which is extremely steep for the initial portion of the envelope. Optical and scanning electron microscope investigations have revealed a dense interpenetrative structure and a considerable degree of grain surface rugosity. These factors give rise to a very high dilation rate before failure, and the dilation rate is suppressed as normal stress increases. The suppression of dilation results in shear of grains and grain asperities, giving rise to an apparent cohesion intercept at higher normal stresses. The curvilinear failure envelopes may be conveniently expressed as power-law relationships, and this form of expression will prove useful in stability analysis.

Description: The Athabasca Oil Sands are largely within the McMurray Formation, which is a transgressive blanket quartz sand of Lower Cretaceous age. Millennia of erosion have resulted in extensive exposures of oil sand along river valleys in the vicinity of Fort McMurray. Study of these slopes has contributed to understanding the nature and behavior of oil sands. Oil sand slopes with active toe erosion are characteristically high and steep (up to 70 m at slopes over 50°), have an indurated outer face and display a stress–relief exfoliation joint system that controls slope recession phenomena. Bitumen does not contribute mechanically to slope stability. The major agents affecting slope morphology are the lithology, the aspect and the basal stratigraphy. Ravelling along exfoliation fractures is the major failure mode, block falls are a minor failure mode and rotational landslides have not been observed. Remolded oil sand may flow viscously, but intact oil sand displays an unusually high strength.