摘要:

During driving of steel piles through soft, sensitive clay into very dense sand and gravel, pore-water pressure responses were monitored. As a result of the large length of the piles and also because of the high sensitivity of the soft clays, the piles were driven in two stages. During the initial stage of driving in the soft clay, only very small pore-water pressure increases were recorded together with very low pile driving resistances; however, during the second stage of driving, high pore-water pressure increases were observed in the clay as soon as the piles penetrated into the underlying very dense sand and gravel. It was concluded that the clay deposit was loaded from below, as the piles were driven into very dense sand. The total stress changes and the resulting pore-water pressure changes in the clay were analyzed, assuming that the pile driving load was equivalent to a flexible load acting on the surface of an elastic half-space, which represents the soft clay deposit. This interpretation of the pore-water pressure increases is important for the assessment of the bearing capacity of engineering structures affected by piles driven through soft soils into very dense deposits. The potential for high pore-water pressure increases in the clay during undrained loading as well as for volume increases in the dense sand due to pile driving can be predicted from piezocone test data.Key words:pile driving, pore-water pressure, piezocone testing, soft sensitive clays, dense sand deposits.

ISSN:0008-3674    

DOI:10.1139/t96-001

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The Bouldery Clay in Singapore consists of sandstone boulders that are embedded in a matrix of very stiff to hard silty and sandy clay. The strength and deformation characteristics of the soil matrix are close to those of a weak rock or a heavily overconsolidated clay. The average value of the second cycle moduli from the pressuremeter tests and the plate load tests is 480 MPa, and the average value of the undrained shear strengh from in situ tests is 1000 kPa. The performance of raft foundations for six high-rise buildings founded on the Bouldery Clay has been vary satisfactory, and the measured maximum and differential settlements are within allowable limits. The average equivalent undrained modulus of elasticity back-calculated from settlement observations is 540 MPa, compared with the average modulus of 480 MPa from in situ tests after unloading and reloading. It is therefore recommended that unloading and reloading of at least two cycles should be carried out for in situ tests so that a more representative modulus of elasticity for the Bouldery Clay and other very stiff or hard soil can be obtained.Key words:raft foundations, Bouldery Clay, Young's modulus, settlement, high-rise buildings.

ISSN:0008-3674    

DOI:10.1139/t96-002

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The strength and deformation characteristics of undisturbed specimens measured by large-scale triaxial tests were compared with those of reconstituted specimens to evaluate the stiffness of natural ground. The undisturbed specimens were sampled from the riverbed gravel foundation of an embankment dam using the freezing sampling method with liquid nitrogen. The validity of the results from the undisturbed specimens was evaluated by comparing the stiffness of the natural ground using P- and S-wave logging (PS logging). The dynamic deformation characteristics (stiffness) of undisturbed specimens are larger than those of reconstitued specimens.Key words:shear modulus, damping ratio, gravel, laboratory test.

ISSN:0008-3674    

DOI:10.1139/t96-003

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

This paper deals with thermo-hydromechanical behaviour of nonsaturated soils. The constitutive relationship presented herein allows for the prediction of the settlement or swell of an unsaturated soil under nonisothermal oedometric conditions. Mechanical, hydraulic, and thermal compression indexes are considered for stress, capillary pressure, and temperature variables, respectively. The implementation of the relationship in a prediction scheme requires preliminary characterization of these indexes. The stress–strain and water volume change relationships are first presented from semiempirical point of view for a nonsaturated soil element under nonisothermal conditions. These relationships allow for the expression of a thermo-hydromechanical constitutive law for nonsaturated soils and propose a relationship for the change in the soil water content. The thermal compression indexes are then determined for a clayey silty sand, first using a reverse method and then a direct method. This determination is made from experimental data recorded on a prototype involving heat storage in an aquifer. The values of these thermal compression indexes are finally compared with the laboratory values obtained in a thermal triaxial cell on samples of the same soil.Key words:nonsaturated soils, thermo-hydromechanical, oedometer tests, thermal compression indexes, characterization, reverse method, direct method.[Journal Translation

ISSN:0008-3674    

DOI:10.1139/t96-004

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The relations between the angle of reach (fahrböschung) and other indexes expressing the mobility of landslides and vertical drop, horizontal reach, and volume of landslide mass have been analyzed by means of simplified plots and regression equations. Results for 204 landslides of all sizes show that whatever the mechanism of motion, all kinds of landslides experience a continuous reduction of the angle of reach with volume increase. This reduction starts from the smallest sizes. Scattering in this relation is mostly due to mechanisms of motion and to both obstacles and topographic constraints on the path. This synthesis indicates that small landslides (less than 0.5 × 106m3), in relative terms, display excesses of travel distance similar to large landslides. Since most small landslides are not expected to develop any change in the mechanism of progression while moving, the decrease in the reach angle with volume suggests that scale effects should be taken into account. The angle of reach is found to be a proper indicator of the relative mobility of landslides and is not dependent on the height of fall.Key words:mass wasting, landslides, reach angle, runout distance, rock avalanches, shallow landslide

ISSN:0008-3674    

DOI:10.1139/t96-005

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The unsaturated shear strength parameter, φb, is usually determined using triaxial of direct shear apparatus that have been modified to allow for the control and (or) measurement of pore-air and pore-water pressures. A fairly high level of expertise is required for the characterization of φbusing these modified apparatus. A simple procedure for determining φbfor statically compacted soils at different water contents is presented along with a method of analysis. The tests can be performed on a conventional direct shear apparatus. The unsaturated shear strength parameter, φb, obtained using the proposed procedure is shown to be comparable to that obtained using the modified direct shear test. Since the proposed procedure utilizes standard laboratory direct shear equipment and takes a relatively short time to complete, it offers an easy and convenient alternative for the determination of φbfor statically compacted soils.Key words:shear strength, matric suction, unsaturated soils, statically compacted soils, direct shear test.

ISSN:0008-3674    

DOI:10.1139/t96-006

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The potential for static and cyclic liquefaction of the sand that underlies the highly seismic Fraser Delta is assessed under simple shear test conditions, typical of an earthquake shaking. A comparison of liquefaction potential is also made between simple shear and conventional triaxial stress conditions. It is shown that the liquefaction potential of sand is profoundly influenced by the stress path. The reduction factors currently applied to the cyclic triaxial resistance for representing simple shear response may involve a large degree of conservatism in design. A direct measurement of soil behaviour under stress conditions typical of earthquake loading may thus have large economic benefits.Key words:sand, liquefaction, static, cyclic, triaxial, simple shear.

ISSN:0008-3674    

DOI:10.1139/t96-007

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A practical numerical model is described for analysis of flexible retaining walls. In terms of capabilities, the model fits between traditional limit equilibrium methods and full finite element approaches; it overcomes many of the limitations associated with the former but is not equipped with the versatility offered by the latter. Using an approach similar to that adopted in boundary-element based models, the wall stiffness is represented by a series of elastic beam elements whose stiffness is combined with that of the prestressed struts and the soil to form, the overall stiffness matrix. The stiffness matrix of the soil is obtained by inversion of flexibility matrices generated by interpolation and sealing of flexibility matrices calculated for a simplified soil model using finite element methods. The soil behaves linearly elastically, as long as the pressures correspond to stress levels lying between the limits. Where the lateral displacement of the wall corresponds to a pressure outside of these allowable limits, correction forces are added until the resulting pressures are within the active or passive pressures. Arching is permitted by considering the forces acting on the wall compared with the forces consistent with possible failure surfaces within the soil. Other features that can be accomodated by the model include struts, variations in water table, and the effects of surcharges. The proposed model has been shown to capture the displacement, anchor loads, and lateral stresses for several field problems. Based on these studies and other field applications of the model a number of points have been observed that are of practical interest; these points are separately listed.Key words:numerical analysis, retaining wall, anchor, arching, soil–structure interaction, deflection

ISSN:0008-3674    

DOI:10.1139/t96-008

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Frequency-domain and time-domain electromagnetic methods were used to investigate groundwater contamination at an active brine pit in southwestern Manitoba, Canada. The objectives of the survey were to delineate contamination suspected to be occuring at the site and to compare frequency-domain electromagnetic (FDEM) and time-domain electromagnetic (TDEM) measurements in a survey area containing pipelines, fences, and power lines. The survey successfully delineated a region of high conductivity around brine pit, confirming that leakage is occurring from the pit. Modelling of the FDEM results suggests the contamination is spreading within a series of shallow sand units. Comparison of FDEM and TDEM survey results indicate that small-separation FDEM systems are much more useful for mapping in a developed area containing sources of cultural noise. The FDEM systems permit rapid mapping of spatial variations in conductivity, are affected to only a limited degree by cultural features, and provide some resolution of the depth variation of conductivity at shallow depth. It was not possible to obtain useful TDEM measurements anywhere near the active brine pit because of the signal distortion in the late-time response.Key words:geophysics, electromagnetic, brine pit, saline contamination.

ISSN:0008-3674    

DOI:10.1139/t96-009

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The finite element analysis of an instrumented geotextile-reinforced test embankment is described and the results are compared with the field measurements. The embankment was constructed to failure on a soft compressible organic clayey silt deposit at Sackville, New Brunswick. The analysis adopts a fully coupled large-strain elasto-plastic Biot consolidation model with modified Cam-clay material behaviour. It is shown that the analysis captured many features of the embankment behaviour. However, it is concluded that the elasto-plastic modified Cam-clay formulation is not adequate for accurately and simultaneously predicting the multiple characteristics (e.g., vertical and horizontal deformations, pore pressures, and geotextile strains) of the embankment behaviour, primarily because of the rate sensitive nature, and the consequent progressive failure of the foundation soil.Key words:embankment, geotextile, reinforcement, analysis, field behaviour, deformations.

ISSN:0008-3674    

DOI:10.1139/t96-010

出版商:NRC Research Press    

年代:1996

数据来源: NRC