ISSN:0008-3674    

DOI:10.1139/t99-114

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Laboratory and field experiments demonstrate that substantial dewatering occurs when the waste clay from oil sands operations is subjected to one cycle of freeze-thaw. The enhanced permeability resulting from the freezing process causes further dewatering and accompanying strength increases during post-thaw consolidation. The findings presented here were guided by a number of different materials handling scenarios which take advantage of the freeze-thaw process and are driven by the appropriate geotechnical, geochemical, and geothermal input parameters. Different conceptual design scenarios are examined to demonstrate how this process might be feasibly implemented at the commercial scale. Emphasis is placed on the large-scale requirements, sensitivity to input parameters, and the coupling of the continuing applied research with the conceptual materials handling models. The latter point is of generic interest to those involved in mine waste management.Key words: mine wastes, freeze-thaw, volume reduction, disposal, large strain consolidation.

ISSN:0008-3674    

DOI:10.1139/t99-028

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

A bounding-surface hypoplasticity model is modified to incorporate the basic premises of critical-state soil mechanics and cover both dense and loose sand behavior. The modification consists of rendering the phase-transformation line a function of the state parameter, which measures the difference between the current and critical void ratios at the same value ofp, such that when the state parameter is zero, the phase-transformation line becomes identical to the critical-state line inq-pspace. As a result the dilatancy depends on the state in a way that yields a zero value at critical state. This dependence allows a realistic modelling of the response of a sand in either loose or dense state, or in the transition from one state to another state. A comparison between model simulations and a sequence of experimental results for drained, undrained, monotonic, and cyclic loading conditions shows that the proposed concept and modelling technique work effectively over a wide range of densities and confining pressures using a unique set of parameters (or parameter dependence) for a given sand.Key words: bounding surface, critical state, dilatancy, phase transformation, soil plasticity, state parameter.

ISSN:0008-3674    

DOI:10.1139/t99-029

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Geotechnical variability is a complex attribute that results from many disparate sources of uncertainties. The three primary sources of geotechnical uncertainties are inherent variability, measurement error, and transformation uncertainty. Inherent soil variability is modeled as a random field, which can be described concisely by the coefficient of variation (COV) and scale of fluctuation. Measurement error is extracted from field measurements using a simple additive probabilistic model or is determined directly from comparative laboratory testing programs. Based on an extensive literature review, the COV of inherent variability, scale of fluctuation, and COV of measurement error are evaluated in detail, along with the general soil type and the approximate range of mean value for which the COVs are applicable. Transformation uncertainty and overall property uncertainty are quantified in a companion paper.Key words: inherent soil variability, measurement error, coefficient of variation, scale of fluctuation, geotechnical variability.

ISSN:0008-3674    

DOI:10.1139/t99-038

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

To evaluate geotechnical variability on a general basis that will facilitate the use of reliability-based design procedures, it is necessary to assess inherent soil variability, measurement error, and transformation uncertainty separately. The inherent variability and measurement error are addressed in a companion paper, and transformation uncertainty is addressed herein. A second-moment probabilistic approach is applied to combine these uncertainties consistently based on the manner in which the design soil property is derived. The design properties considered in this paper are undrained shear strength, effective stress friction angle, in situ horizontal stress coefficient, and Young's modulus. This paper concludes with specific guidelines on the typical coefficients of variation for these common design soil properties as a function of the test type and the type of correlation used.Key words: transformation uncertainty, undrained shear strength, friction angle, in situ horizontal stress coefficient, Young's modulus, geotechnical variability.

ISSN:0008-3674    

DOI:10.1139/t99-039

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The suction profile of a desiccating soil is dependent on the water table depth, the soil-water retention characteristics, and the climatic conditions. In this paper, an unsaturated flow model, which simulates both liquid and vapour flow, was used to investigate the effects of varying the water table depth and the evaporation rate on the evaporative fluxes from a desiccating tailings deposit under steady-state conditions. Results obtained showed that at a critical evaporation rate, beyond which evaporation is no longer dictated by climatic conditions, the matric suction profiles remain basically unchanged. The critical evaporation rate varies inversely with the water table depth. It is associated with the maximum evaporative flux that might be extracted from a soil at steady-state conditions. The time required to establish steady-state conditions is directly proportional to the water table depth, and it acquires a maximum value at the critical evaporation rate. A detailed investigation of the movement of the drying front demonstrated the significance of attaining a matric suction of about 3000 kPa on the contribution to flow in the vapour phase.Key words: matric suction, mine tailings, potential evaporation, steady state evaporative conditions, surface evaporative flux.

ISSN:0008-3674    

DOI:10.1139/t99-030

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The focus of this paper is on the development and validation of a numerical model of flow through simplified embankment dams with fractures. Two laboratory experiments were conducted to provide data for validation of the numerical model, one dealing with steady flow in a Hele-Shaw cell and one with steady flow through a bed of packed glass beads. A horizontal fracture, extending from the upstream boundary to a point within the embankment, was used in both experiments, and it was shown to have a significant influence on the discharge, pressure distribution, height of the seepage face, and free surface profile. Comparisons between numerically determined and experimentally measured results were carried out with respect to the discharge, pressure distribution, height of the seepage face, and free surface profile. In the experiments it is shown that a fracture increases the discharge and that the discharge increases more when a fracture is located far away from the free surface profile than when it is located close to the free surface profile. The height of the seepage face above the tailwater is strongly dependent upon the length of the fracture. The influence on the free surface profile is greater when a fracture is close to the free surface profile than when it is far away from the free surface profile. These effects are also found in the numerical simulations. It is thus concluded that the agreement is generally satisfactory between the experimental and numerical results.Key words: numerical model, embankment dam, fracture, experimental data, discharge.

ISSN:0008-3674    

DOI:10.1139/t99-032

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Salt rocks, such as potash and rock salt, show a complex mechanical behavior that is rate and history dependent. Various approaches exist to represent the main features of the response of these rocks through constitutive models. The approach proposed in this paper is to formulate the constitutive equations using internal state variables (ISV) in the context of the unified theory of inelastic flow. To illustrate the application of this approach, the authors use an updated version of a viscoplastic model with reduced expressions for laboratory triaxial tests at relatively high confining pressure. It is shown that, under these conditions, mixed hardening of salt rocks can be described through a combination of scalar and directional ISV. The authors also describe in some detail a procedure to obtain the material parameters for the model equations. The paper shows some characteristics of the model response for various loading paths, illustrating the good agreement with experimental observations and highlighting some of the differences with a classical isotropic hardening model.

ISSN:0008-3674    

DOI:10.1139/t99-033

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

This paper summarizes the findings from an experimental program concerning the hydromechanical behavior of two smectite clays tested under high stresses. Increasing axial stress on the smectite samples under controlled relative humidity (suction) leads to collapse in the soil structure and increases the degree of saturation. Irreversible volume change is observed in samples tested under cyclic suction with constant axial load. Water-retention (adsorption and desorption) behavior of the smectite clays tested in this study is affected by particle size, initial void ratio, and confinement conditions during the tests. Laponite, which has a large specific surface area, tends to hold more water than hectorite at a given relative humidity. More water is adsorbed by samples compacted at lower axial stress.Key words: smectite clays, hydromechanical stresses, behavior, relative humidity and suction, water retention, degree of saturation.

ISSN:0008-3674    

DOI:10.1139/t99-035

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The findings from a rare opportunity to exhume, examine, and sample a granular underdrain leachate collection system at a large municipal landfill site are reported. The "clear stone" drainage blanket was constructed from uniform, coarse gravel (with a nominal 50 mm particle size) obtained by crushing dolomitic limestone. After exposure to municipal landfill leachate for 1-4 years, the drainage stone was found to contain a considerable mass and volume of clog and slime materials. These were composed of mineral precipitates, fine granular particulate, and biofilm, growing under the ambient anaerobic conditions prevalent below the landfilled waste. The spatial distribution, physical and hydraulic properties, and chemical and microbiological composition of this material were examined and compared with similar material recovered from a laboratory mesocosm. The findings suggest a theoretical framework for a model of clogging behaviour of leachate collection drains at municipal solid waste landfill sites.Key words: municipal waste, leachate, clogging, drainage, biofilm, cementation.

ISSN:0008-3674    

DOI:10.1139/t99-036

出版商:NRC Research Press    

年代:1999

数据来源: NRC