摘要:

According to stability postulates by other authors, soils that exhibit nonassociated flow may become unstable when exposed to certain stress paths inside the failure surface. Several series of conventional triaxial tests on fully saturated specimens have been performed to study the regions of stable and unstable behavior. For saturated specimens that tend to compress, undrained conditions lead to effective stress paths directed within the region of potential instability, and instability is observed, provided the yield surface opens up in the outward direction of the hydrostatic axis. Thus, instability occurs inside the failure surface. Instability is not synonymous with failure, although both lead to catastrophic events. The location of the region of potential instability and its determination are discussed. The submarine Nerlerk berm, which suffered six slides during its construction, is analyzed using a newly developed method of instability analysis. It is shown that conventional slope stability methods do not capture the mechanics of instability and subsequent liquefaction. The proposed analysis method is based on the location of the region of potential instability and the stress state in the ground. In addition, a trigger mechanism is required to initiate the instability. These topics are discussed with reference to the slides in the Nerlerk berm.Key words: instability, nonassociated flow, plastic properties, sand, shear strength, submarine slope.

ISSN:0008-3674    

DOI:10.1139/t93-088

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

A generalized model for three-dimensional analysis, using the method of columns, is presented. The model is an extension of the two-dimensional general limit equilibrium formulation. Intercolumn force functions of arbitrary shape can be specified to simulate various directions for the intercolumn resultant forces. A unique feature of the model involves the use of a geostatistical procedure (i.e., the Kriging technique) in modelling the geometry of the slope, the stratigraphy, the potential slip surface, and the pore-water pressure conditions. The technique simplifies the data-input procedure and expedites the column discretization and the factor of safety computations. The shape of the intercolumn force functions was investigated for several slope geometries using a three-dimensional finite element stress analysis. The significance of the intercolumn force functions in three-dimensional stability analyses was also studied. The model was utilized to study a case history involving an open-pit mining failure. The results indicate that the model is able to provide a more realistic simulation of the case history than was possible using a conventional two-dimensional model.Key words: stability analysis, general limit equilibrium, three-dimensional, method of columns, factor of safety.

ISSN:0008-3674    

DOI:10.1139/t93-089

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Natural Ca-montmorillonite clay soils or engineered clay barriers in western Canada are often used to contain brine generated from the surface disposal of potash tailings or from drilling activities associated with the oil and gas industry. The performance of these barriers has ranged from excellent to poor. The influence of salt brines on the geotechnical properties of these soils has been recognized as a potentially important factor for some time. It has been well documented in the literature that the behavior of clayey soils is strongly influenced by physicochemical interactions between clay particles and pore-fluid chemistry; consequently, the properties of these soils are sensitive to changes in the electrolyte concentration of the pore fluid. An increase in the concentration of the pore fluid to the levels of a concentrated brine can cause significant changes in the geotechnical properties of the soil. In this paper, the impact of brine contamination on the geotechnical properties of two Ca-montmorillonitic clayey soils of glacial origin from western Canada is reviewed. The influence of clay–brine interactions on the index properties (liquid limit, plastic limit, plastic index, mineralogy, density, grain size, and compaction characteristics), mechanical properties (volume change and shear strength), and hydraulic properties (hydraulic conductivity) is described. A quantitative explanation for the changes that occur in the hydraulic and mechanical properties of these soils as a result of brine permeation is also provided. This explanation relates the changes in pore-fluid chemistry to changes in an effective physicochemical stress state. This approach may be used to predict the changes in hydraulic conductivity, volume, or shear strength of a clayey soil as a result of brine contamination.Key words: clay–brine interactions, diffuse double layer, hydraulic conductivity, soil structure, physicochemical.

ISSN:0008-3674    

DOI:10.1139/t93-090

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The method of thickened tailings disposal has been in use at an active copper–zinc mine near Timmins, Ontario, for approximately 25 years. The thickened tailings deposit that has been formed was investigated. Field and laboratory tests were conducted to determine particle-size distribution at various horizontal locations, in situ values of hydraulic conductivity, moisture-retention characteristics, groundwater levels, and in situ water contents. The results of the investigation show that the thickened tailings deposit is relatively homogeneous. Shallow groundwater levels were also observed to follow the gently sloping topography of the tailings surface. Upward-seepage analyses were conducted for various steady-state evaporative fluxes. The analyses showed the tailings tend to maintain saturated conditions for the highest potential rate of evaporation observed. The ability of the tailings to maintain saturation is attributed to the shallow groundwater levels and the high air-entry value of the tailings. The tendency to saturated conditions at the tailings surface is a positive result. Saturated conditions in the tailings minimize the diffusion of atmospheric oxygen into the tailings. This aids in the prevention of acid generation in these tailings, which have the potential to oxidize and produce acid drainage.Key words: tailings, saturation, evaporation, acid generation.

ISSN:0008-3674    

DOI:10.1139/t93-091

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Two analytical models for snow creep and glide forces on structures in deep snow covers are compared theoretically and checked against field data. The results show that the formulations contained in the 1990 Swiss guidelines for avalanche defence are incompatible with a continuum mechanical model based on linear creep and glide constitutive equations. In addition, the formulations in the 1990 Swiss guidelines neglect the pressure from the component of body force in the slope-normal direction, which is an unnecessary simplification.Key words: snow pressure, quasi-static, creep, glide, deep snow cover, continuum.

ISSN:0008-3674    

DOI:10.1139/t93-092

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The drained behaviour of loose sands under simultaneous increase in stress ratio and principal stress rotation is investigated. The hollow cylinder torsional device, which permits independent control of four stress parameters, namely effective mean normal stress, stress ratioR, intermediate principal stress parameterb, and the inclination ασof the major principal effective stressto the vertical, is adopted as the testing device. Drained tests carried out on saturated sand indicate that deformations under increasingRand ασare path independent, if the final stress state is within the approximate bounds ofR < 2 and ασ < 45°. With increasing stress ratioRand (or) principal stress rotation, deformations gradually become path dependent. Once loaded to a stress state within the domainR < 2 and ασ < 45°, the strain response under subsequent principal stress rotation is shown to be independent of the previous loading history. It is demonstrated that the strain response under any general increasingR − ασpath in the domain ofR < 2 and ασ < 45° can be predicted using the results of a limited number of tests characterizing that domain. Strain increment direction αΔϵis shown to be approximately coincident with and totally governed by the stress increment direction αΔσ, when the stress increment direction αΔσis preferentially inclined towards the vertical deposition direction.Key words: sand behaviour, hollow cylinder torsional device, principal stress rotation, stress-path testing.

ISSN:0008-3674    

DOI:10.1139/t93-093

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The injection of grout in the microfissures of concrete dams in operation is very tricky because of the high pressures required to penetrate the slightly opened fissures. These conditions of grouting may result in the propagation of the fissures and contribute to the loss of stability of the mass. The technique using acoustical emission to follow the injection in real time has been evaluated. Water injection tests have been carried out on large dimensions (2.64 m × 1.42 m × 0.40 m) fissured concrete slabs instrumented with pressure, load, and displacement transducers. According to a study comparing two types of acoustical emission transducers, the low-frequency transducers would be more appropriate for this type of application. Moreover, the detected acoustical signals are not due to a constant pressure flow, but to the accelerations and decelerations of the grout, and to the mechanisms resulting from the variations of pressure and flow of the fluid (opening and closure of the fissure). Thus these observations confirm that the acoustical emission may be an interesting means to control the injections and, in particular, to determine the process of grout flow.Key words: concrete, fissure, injection, water test, pressure, acoustical emission. [Journal translation]

ISSN:0008-3674    

DOI:10.1139/t93-094

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Deficiency investigations were undertaken at Hugh Keenleyside Dam, near Castlegar, British Columbia, to identify the nature and sources of foundation defects responsible for high uplift pressures under a section of the concrete dam. Several techniques employed in the investigations proved particularly useful in delineating the defects. These were temperature surveys and chemical analysis of flows from pressure instruments and foundation drains, air-injection tests, foundation coring and installation of additional piezometers. A comprehensive program of pressure response testing of cells, piezometers, and drains was also carried out to establish the interconnections within the rock foundation. Detailed assessments of construction records to assemble relevant geological and foundation conditions, foundation excavation, preparation, and treatment aspects, and particular structural foundations were vital in discerning the cause for the high uplift pressures. Piping of a relatively thin, upstream, impervious till blanket (required for the earthfill dam) on blast-induced, highly fractured rock extending under the structure was found to be the defect responsible for reservoir leakage and high uplift pressures.Key words: uplift pressures, concrete dam, foundation drains, piezometers, uplift cells, temperature survey.

ISSN:0008-3674    

DOI:10.1139/t93-095

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Of the existing in situ stress-measurement techniques, the doorstopper is particularly suited for use in highly stressed zones where core discing may occur. The main reason is that the doorstopper requires a very short intact core length to obtain a valid measurement in comparison with other techniques that use overcoring to perform stress relief, such as borehole-deformation gauges, CSIR (Council for Scientific and Industrial Research), and CSIRO (Commonwealth Scientific and Industrial Research Organization) gauges. The paper presents stress-measurement results obtained with the modified doorstopper technique in highly stressed granite, at the Underground Research Laboratory (URL) of Atomic Energy of Canada Limited. A brief description of the modified doorstopper technique and of a stress-calculation model that includes the nonlinear anisotropic behaviour found in highly stressed rocks is made. Stress-measurement results obtained at the URL with different techniques are compared with those obtained with the modified doorstopper cell.Key words: doorstopper, high stresses, anisotropy, nonlinear elasticity, core discing.

ISSN:0008-3674    

DOI:10.1139/t93-096

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Alberta's largest historic landslide dammed the Saddle River near Rycroft, Alberta, and thrust the bed of the river upward against the opposite valley wall forming a type 6 landslide dam. The Rycroft landslide occurred within a day or two of 17 June 1990 on the north wall of the Saddle River, 12 km northeast of Rycroft, Alberta. The triggers for the landslide are considered to be the lateral and vertical erosion of the river as a result of a severe rainstorm and the ensuing flood. The slide scarp arcs for 1 km through a cultivated field. The loss of farmed land was 13 h (32 acres); a further 10 h (25 acres) may be lost by retrogression of the scarp. The toe heaved the riverbed upward as much as 20 m and thrust it laterally 60 m to be compressed against the opposite valley wall. About 40 Mm3of ground moved. The rupture surface dipped steeply through postglacial lake clay and till, curved abruptly to pass on a subhorizontal surface through preglacial clay, then curved upward under the riverbed. This preglacial clay is a new factor in landslide assessment in northwestern Alberta.Key words: landslide, landslide dam, Interior Plains, preglacial clays.

ISSN:0008-3674    

DOI:10.1139/t93-097

出版商:NRC Research Press    

年代:1993

数据来源: NRC