摘要:

This paper presents the results of a 3 year monitoring program of the volumetric water content in two clay deposits on Montréal Island. The water content was monitored by means of a neutron depth moisture probe, which was lowered down in a series of 3–6 m deep, permanently installed, aluminium access tubes. These tubes are located at various distances from deep-rooted trees on two experimental sites. On the first site, a two-storey reinforced concrete building, surrounded by four rows of 15–20 m high silver maples, has suffered a differential settlement of over 150 mm. On the second site, a three-storey apartment block, surrounded on two sides by a row of 5–10 m high maples, has suffered a differential settlement of about 50 mm. The paper analyses the volumetric water content variations and compares them with both the rainfall deficits calculated for the period of observation and the elevation profiles of the building foundations. In addition, a comparison is made between the observed damages and a classification proposed by the Building Research Establishment of England.Key words: volumetric water content, trees, settlement, distortions, clay deposits, seasonal variations, damages.

ISSN:0008-3674    

DOI:10.1139/t92-021

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The design of underground openings in horizontally layered strata on the basis of classical linear arching theory assumes the ultimate load capacity of the roof is limited by crushing or compressional failure at the centre of the arch or at the abutments. In this study, physical model tests on limestone, granite, and potash beams revealed a progressive failure mechanism dominated by discrete tensile fracturing, a quite different failure process to that assumed by classical theory. Subsequently, discrete crack propagation finite element analysis successfully simulated the failure mechanisms observed in the physical models.Key words: rock mechanics, underground design, roof stability, Voussoir arch, fracture.

ISSN:0008-3674    

DOI:10.1139/t92-022

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The paper presents the volume change theory and the designation of associated soil properties that must be measured for an unsaturated soil. The equipment required for the measurement of each of the relevant volume relationships is described. Several testing procedures for obtaining the volume change indices during loading and unloading of an unsaturated soil are presented. Typical results from loading and unloading tests on compacted silt and compacted glacial till specimens are presented and analyzed. The analysis is given in order to illustrate the application of the volume change theory to practical problems.Key words: unsaturated soil, volume change indices, constitutive relations, coefficients of volume change, oedometer tests.

ISSN:0008-3674    

DOI:10.1139/t92-023

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Results of an investigation of the response of piles in sand, under lateral loads, are presented. Model piles of three different diameters and flexural stiffnesses were tested in a centrifuge apparatus to determine prototype pile behavior. The experimental results, consisting of pile head displacements and bending moment distributions along the pile length, were interpreted, analyzed, and compared with the results of several numerical analyses. The piles were treated as elastic beams on nonlinear springs, examining several different types of soil reaction relationship (p-ycurves). A newp-yrelationship was developed for piles in cohesionless soil which provided very satisfactory results.Key words: pile, sand, lateral loading, centrifuge, numerical analysis.

ISSN:0008-3674    

DOI:10.1139/t92-024

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The project is concerned with the acquisition of reliable data from large-scale silos, and in particular data relating to pressures imposed on the silo by the stored material. For the purposes of the study a square plan-form steel silo was used, and the stored material was Leighton Buzzard sand. The experimental work was carried out in the environmentally controlled conditions of the laboratories at Building Research Establishment, Watford, United Kingdom. The project adopted the pressure cells designed by V. Askegaard. Both wall cells and embedded cells were used to measure pressure at the interface of the wall and stored material and within the stored material, respectively. For the embedded cells, it has been shown that the installation procedure is critical in obtaining reliable results. Preliminary tests were carried out in small-scale models until confidence in repeatability of the placement method was achieved. Even then there was some variation in results, and to ensure confidence each large-scale test was repeated five times. Pressures measured by both wall and embedded cells were compared to obtain calibration factors, and then the overall vertical equilibrium of the model was checked and found to be within the bounds of experimental error. The authors are confident of the accuracy of data which can now be achieved provided care is taken with both installation procedures and calibration checks.Key words: pressure measurement, silos, granular media, pressure cell calibration.

ISSN:0008-3674    

DOI:10.1139/t92-025

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The minimum factor of safety of a slope can be found by using various methods of optimization or by random search. This paper presents a combined approach that uses the random search to find an estimate of the global minimum which is employed by the methods of optimization as a starting point. Guidelines have been given to select an appropriate number of random trials. Two simplified methods for calculating the factors of safety are suggested to minimize the computing time of the random searches. The approach has proved to be more efficient than either a purely stochastic or a deterministic one.Key words: slope stability, landslide, factor of safety, critical slip surface, method of optimization, random search, Monte Carlo method.

ISSN:0008-3674    

DOI:10.1139/t92-026

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

This paper examines the behaviour of dense, nonaqueous phase liquids (DNAPLs) in fractured media, with an emphasis on waste-disposal ponds constructed in fractured clay and rock. Calculations are presented to estimate the height of DNAPL that may accumulate at the base of a disposal pond prior to initial entry into a water-saturated fracture. This height is found to be a function of the fluid densities, the DNAPL–water interfacial tension, the fracture aperture, and the position of the water table. A numerical model is applied to estimate the steady-state rate of DNAPL leakage from a disposal pond underlain by vertical fractures. This rate of leakage is found to be a function of the spacing of fractures, the fracture aperture, the DNAPL density, and the height of the water table in the formation outside of the impoundment. It is demonstrated that a wide range of leakage rates can occur over a relatively narrow range of parameters. A conceptual analysis of two-phase flow examines the conditions that lead to both uniform and sparse DNAPL migration pathways beneath a disposal pond in fracture networks. A case history is presented as field evidence of the concepts discussed. In particular, the case history demonstrates that sparse DNAPL migration pathways can occur in fractured rock, and that relatively low dissolved phase concentrations can exist in the immediate vicinity of DNAPL source zones.Key words: nonaqueous phase liquids, ground water, fractures, disposal ponds.

ISSN:0008-3674    

DOI:10.1139/t92-027

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Three different 406 mm diameter piles were tested with lateral, vertical, and moment loadings. The purpose of the full-scale field tests was to assess the ability of the piles to withstand large lateral deformations that may be caused by earthquake-induced soil liquefaction. Two concrete shaft piles were tested to failure with lateral displacements at the pile top of up to 300 and 650 mm and pile curvatures of up to 0.16 and 0.35 rad/m, respectively. The third pile, a concrete-filled steel pipe shaft pile, reached a maximum lateral displacement at the pile top of 550 mm and a curvature of 0.08 rad/m without failure or significant distress. It is concluded that stronger piles that push through the soil may tolerate larger lateral displacements than weaker piles and that reducing the spiral reinforcing pitch from 150to 100 mm on concrete piles greatly increases the pile ductility.Key words: lateral load test, piles, reinforced concrete, concrete-filled pipe, seismic, liquefaction, pile curvature.

ISSN:0008-3674    

DOI:10.1139/t92-028

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The relationship between molding water content and hydraulic conductivity of a compacted sand-bentonite mixture was examined in a laboratory test program. This program involved triaxial permeability testing of nine specimens of 8% bentonite and Ottawa sand, compacted at standard Proctor density using molding water contents ranging from6 to 19%. The permeability tests were conducted using hydraulic gradients ranging from 19 to 40. The specimens were subjected to an average effective stress during testing of 21 kPa. The tests were conducted using continuous back pressure saturation. Each test was run for a minimum of 40 000 min (approximately 28 days) to enable the flow in and out of the specimen to come to equilibrium with respect to each other. The hydraulic conductivity decreased from 6.5 × 10−9 cm/s for a molding water content of 5.9% to 1.4 × 10−9 cm/s for a molding water content of 15.8%. However, although the hydraulic conductivity was related to the molding water content, the variation in hydraulic conductivity was relatively small. Therefore, the low values reported for all hydraulic conductivity tests suggest that molding water content is not a critical design factor in the construction of a low-permeability sand-bentonite liner.Key words: molding water content, bentonite, liners, hydraulic conductivity, triaxial permeability testing, covers, sand.

ISSN:0008-3674    

DOI:10.1139/t92-029

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Cracking in soils that are undergoing drying is controlled by soil suctions and by soil properties such as compression modulus, Poisson's ratio, shear strength, tensile strength, and specific surface energy. The paper reviews the occurrence and morphology of cracks in dry-climate regions of Australia and Canada. After reviewing the behaviour of unsaturated soils and the mechanics of cracking, solutions are developed based on (i) elasticity theory, (ii) the transition between tensile and shear failure, and (iii) linear elastic fracture mechanics. The solutions are compared and related to crack depths observed in the field.Key words: clay, cracks, crust, shear strength, soil suction, tensile strength, unsaturated soil, weathering.

ISSN:0008-3674    

DOI:10.1139/t92-030

出版商:NRC Research Press    

年代:1992

数据来源: NRC