摘要:

Mobilization of the pullout resistance of geosynthetics in monotonic and cyclic modes is described from both displacement- and load-controlled tests performed at normal stresses in the range 4-17 kPa. The tests were performed on three geogrids and two geomembranes embedded nearly 1.0 m in a uniformly graded sand. Results for load-controlled tests at a constant rate of 0.25 kN/(m ·min-1), followed by several series of load cycles of increasing amplitude, are compared with displacement-controlled tests at a constant rate of 0.5 mm/min. In general the geogrids behave as an equivalent textured sheet. Pullout behaviour, and especially the incremental displacement mobilized at cyclic loads close to the maximum resistance, is found to vary with type of geogrid. In only one case was cyclic pullout resistance of a grid found to exceed the monotonic resistance. A comparison of the cyclic and monotonic response yields a constant ratio of pullout resistance at large displacement, but one which is not unique to a particular specimen. Cyclic strains of decreasing amplitude are mobilized along a test specimen, with most of the necessary relative displacement occurring close to the loaded end and the embedded end showing little response.Key words: pullout testing, monotonic, cyclic, dynamic, geosynthetics, reinforced walls.

ISSN:0008-3674    

DOI:10.1139/t97-088

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Triaxial compression tests were performed on unsaturated sand-bentonite buffer at elevated temperatures and pressures. Air and water drainage lines from the specimen were generally kept closed through (i) heating, (ii) pressuring, and (iii) shearing. The tests can therefore be characterized as undrained-undrained-undrained tests. Effects of open drainage were also explored. Confining pressures ranged from 0.2 to 3.0 MPa at temperatures of 26, 65, and 100°C. Specimens were statically compacted to a constant dry density of 1.67 Mg/m3, and to degrees of saturation between 35 and 98%. Suction - water content relationships were established to determine the initial total suction before testing. Results indicate that undrained strengths increase with decreasing degree of saturation (50 <=Sr<= 100%), with increasing confining pressure, and with decreasing temperature. The normalized compression modulusE50/sudoes not respond monotonically to changes in saturation, pressure, and temperature. Changes in strength and stiffness have been described in relation to net mean stress and suction in shear strength - net mean stress - suction space.Key words: sand-bentonite, unsaturated, suctions, temperature, strength, stiffness, structure.

ISSN:0008-3674    

DOI:10.1139/t97-093

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Free swell, semiconfined swell, and one-dimensional oedometer swell tests were performed on La Biche shale specimens in solutions of different salinities. The swelling behaviour of La Biche shale was found to be highly anisotropic and dependent on electrolyte concentration, stress, and swelling history. Drained triaxial compression tests were conducted on La Biche shale specimens subjected to different degrees of swelling. The test results indicate that the Young's modulus decreases with increasing swelling. The strength loss due to swelling can be explained by the Hvorslev failure theory. A descending power law is proposed to describe the cohesion reduction with the swelling.Key words: shale, salinity, swelling, strength weakening, modulus softening.

ISSN:0008-3674    

DOI:10.1139/t97-087

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Recent work at the Underground Research Laboratory of Atomic Energy of Canada Limited in Pinawa, Manitoba, has shown that high compressive stresses near the tunnel face significantly contribute to the loss of strength, and eventual failure of the rock, through stress-induced brittle fracturing. A program of laboratory testing has been undertaken to investigate the effects of brittle fracture on the progressive degradation of rock mass strength. The work carried out in this study involves a detailed analysis of the crack initiation and propagation thresholds, two key components in the brittle-fracture process. This paper describes new techniques developed to enhance existing strain gauge and acoustic emission methodologies with respect to the detection of these thresholds and their effects on the degradation of material strength.Key words: tunnel, rock failure, brittle fracture, crack initiation, crack propagation.

ISSN:0008-3674    

DOI:10.1139/t97-091

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A geothermal model is described that simulates simultaneous deposition, freezing, and thawing of mine tailings or sequentially placed layers of embankment soil. When layers of soil or mine tailings are placed during winter subfreezing conditions, frozen layers are formed in the soil profile that may persist with time. The following summer, warmer soil placement may not be sufficient to thaw out layers from the preceding winter. Remnant frozen soil layers may persist for many years or decades. The analysis is unique, as it involves a moving upper boundary and different surface snow cover functions applied in winter time. The model is calibrated based on two uranium mines in northern Saskatchewan. The Rabbit Lake scenario involves tailings growth to a height of 120 m over a period of 24 years. At Key Lake, tailings increase in height at a rate of 1.3 m/year. Good agreement between the observed position of frozen layers and those predicted by the model is obtained. Long-term predictions indicate that from 80 to 200 years would be required to thaw out the frozen layers formed during placement, assuming 1992 placement conditions continue. Deposition rates of 1.5-3 m/year give the largest amounts of frozen ground. The amount of frozen ground is sensitive to the assumed snow cover function during winter.Key words: geothermal, model, tailings, freezing, deposition.

ISSN:0008-3674    

DOI:10.1139/t97-081

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

This paper shows the results of large settlements observed over several years in Belgrade for a hotel founded on four rectangular rafts with expansion joints of 1 m width, and for a silo group built on the right bank of the Danube River. The capacity of the silo group is 400 MN. The settlement calculation for these structures was made using deformation parameters deduced from cone penetration test results. The theoretical solution for stresses and displacements was obtained by the finite difference method. Observed and calculated settlements show satisfactory agreement.Key words: settlement, raft foundation, finite difference, cone penetration tests.

ISSN:0008-3674    

DOI:10.1139/t97-090

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Finite element computer programs are frequently used to analyze and design embankments and similar earth structures. In most of the available computer programs, lack of a proper constitutive relationship to deal with volume change when an increase in the degree of saturation occurs, namely collapse phenomena, is a major handicap. In this paper, volume change results obtained from isotropic compression tests conducted on unsaturated compacted soil specimens are presented. Dependence of the bulk modulus of the soil on water content is investigated. Next, a hyperbolic formulation for volume change behavior of unsaturated soils taking into account variation of soil water content is presented. This hyperbolic model relates mean applied stress, volume change, and water content and represents a three-dimensional surface, the so-called "state surface". Suitability of the proposed model to predict collapse phenomena is verified by examining the model prediction against available experimental data.Key words: hyperbolic, unsaturated soil, collapse, volume change, suction pressure, bulk modulus.

ISSN:0008-3674    

DOI:10.1139/t97-089

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A fundamental study of the undrained behaviour of sands under multiaxial loading is presented. The investigation was carried out using Fraser River and Syncrude sands in a hollow cylinder torsional shear device. Shear loading was carried out under strain control to capture the postpeak strain-softening characteristics of loose sands. It is shown that the undrained response of loose sands is highly dependent on the loading direction. The friction angle mobilized at phase transformation and steady state is a unique material property, independent of the mode of loading, direction of principal stress and initial consolidation stress, and void ratio state. There is no unique relationship between steady state strength and void ratio which is independent of stress path and the level of initial confining stress.Key words: anisotropy, hollow cylinder torsional shear, liquefaction, sand, simple shear, triaxial.

ISSN:0008-3674    

DOI:10.1139/t98-007

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Foundation movements at the Syncrude tailings dyke continued over several years in response to the construction of the dyke. Major movements have been observed in a relatively narrow layer of previously sheared clay-shale material of the Clearwater Formation. The residual strength of this highly plastic clay increases with the rate of shear. By reviewing the existing literature on the rate effects on residual strength and using data from new experiments on Clearwater Clay Shale, a general correlation between soil plasticity and rate effects is found. This rate dependence of the residual strength of Clearwater clay shale has been incorporated into a deformation analysis, which made it possible to compute time-dependent movements of the foundation soil to a satisfactory level. By using a rate-dependent plasticity model, a prediction of anticipated foundation velocities and how they decrease with time may be achieved.Key words: finite element, rate effects, residual strength, Syncrude tailings dyke, time-dependent movements.

ISSN:0008-3674    

DOI:10.1139/t97-086

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The Frank slide, involving an estimated 30 million m3of rock occurred in 1903 on the east face of Turtle Mountain, southwestern Alberta, Canada. It resulted in the loss of approximately 70 lives. Numerous authors have discussed the mechanism of the slide, with both limit equilibrium and elastic finite element analyses being conducted. This paper represents the first published account of the application of elasto-plastic finite difference and distinct element techniques to the Frank slide. It constitutes an attempt to improve our understanding of the ground deformation processes involved. The results of an extensive elasto-plastic modelling study illustrate that although the prime cause of the slide was the adverse geological structure, mining at the base of Turtle mountain could have acted as a final triggering mechanism. This appears to be in agreement with accounts published at the time of the disaster.Key words: landslides, numerical modelling.

ISSN:0008-3674    

DOI:10.1139/t98-005

出版商:NRC Research Press    

年代:1998

数据来源: NRC