摘要:

A study is presented of the transfer of heat within a saturated sand with reference to the analysis of artificial freezing of the ground. First, the main characteristics of the adopted finite element approach and of the technique that introduces the latent-heat effects during the water–ice phase transition are illustrated. Subsequently, the results of some laboratory freezing tests are presented on the basis of which the computer program and the procedure for working out the thermal constants of the soil were calibrated. Finally, a parametric study is discussed that concerns the effects of pipe diameter, distance between pipes, and coolant temperature on the progress of the 0 °C isotherm.Key words: artificial freezing, finite elements, heat transfer, laboratory test, Stefan problem.

ISSN:0008-3674    

DOI:10.1139/t94-001

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

In this paper an ultimate bearing capacity risk-reduction factor is proposed to account for the variation and randomness in soil properties. Through a first-order Taylor series expansion, the mean and variance of the ultimate bearing capacity were assessed. Consequently, the variation of the ultimate bearing capacity is expressed as a function of the variation in cohesion and internal friction angle. To develop a risk-reduction factor, several probability density functions were utilized. The asymptotic type II extreme-value distribution for maxima was found best suited to represent the ultimate bearing capacity. The results indicate that the risk-reduction factorFRdecreases with an increase in the coefficient of variation of ultimate bearing capacity and a decrease in the selected probability of failurepf. Forpf = 0.0001, however,FRwas found to range between 0.20 and 1.0. A numerical example is presented to illustrate the use of the proposed reduction factor.Key words: bearing capacity, coefficient of variation, probability distribution, probability of failure, risk factor, shallow foundations.

ISSN:0008-3674    

DOI:10.1139/t94-002

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Relationships between durability and lithologic characteristics of 61 mudrock samples from North America were investigated with the objective of developing a mudrock-durability classification based on lithologic characteristics. Second-cycle slake-durability index (Id2) was used as a measure of durability, whereas clay content, clay-mineral composition, texture, microfracture frequency, absorption, adsorption, dry density, void ratio, and Atterberg limits were used to characterize mudrock lithology. Based upon the amount of clay-size material, the presence or absence of laminations, and the degree of induration, the mudrocks were subdivided into claystones, mudstones, siltstones, shales, and argillites. The relationships between durability and lithologic characteristics were investigated separately for each class of mudrocks. The results show that different lithologic characteristics best correlate with the durability of each class of mudrocks. The durability of claystones correlates best with the amount of expandable clay minerals and that of mudstones with the frequency of microfractures. The degree of consolidation, as expressed by absorption, influences the durability of both siltstones and shales. The durability of argillites is related to their crystalline texture. Lithologic characteristics can be quantitatively related to a durability classification proposed herein that recognizes three classes of durability: low (Id2 < 50%), medium (Id2 = 50%–85%), and high (Id2 > 85%).Key words: mudrock, durability, lithologic characteristics, classification.

ISSN:0008-3674    

DOI:10.1139/t94-003

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Results are presented from several series of centrifuge model tests of piles installed in beds of uniform dry sand. Using identical model geometries, but varying acceleration factors, the tests demonstrate quite clearly the nature and extent of stress-level variations on the performance of piles. The results are interpreted initially in terms of bearing capacity coefficientsNtand lateral earth pressure coefficientsKs, and subsequently in terms of angle of friction, determined using available relationships. Controlled laboratory experiments with varying levels of overburden pressure around the piles indicated consistent reductions inNt, and to a lesser extent inKs. Quantitative interpretations in terms of angle of friction variations depend on selection from a range of empirical correlations available and have been made for two of those commonly used. Comparison of shaft loads in compression and extension confirms the widespread belief that there is a difference, which is found to vary quantitatively depending on the relative density.Key words: model tests, piles, sand, centrifuge, stress level.

ISSN:0008-3674    

DOI:10.1139/t94-004

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

This paper describes the recent concept of equivalent time and how it can be used in a revised version of an earlier elastic viscoplastic model for one-dimensional straining of clays. It clarifies how parameters in the model can be determined using data from single-stage or multistage creep tests. The model can describe one-dimensional stress or strain responses under general conditions that include multistage loading with creep straining, continuous loading, and unloading or reloading. It also describes modelling for constant rate of straining tests, constant rate of stressing tests, and relaxation tests. Preconsolidation pressures are shown to depend on unloading–reloading, aging, and other loading processes.Key words: clay, compression, creep, equivalent time, elastic viscoplastic, preconsolidation pressure.

ISSN:0008-3674    

DOI:10.1139/t94-005

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The effect of overburden pressure on liquefaction resistance of sand is studied and results of a site-specific investigation are presented. When estimating liquefaction resistance of sand from the indirect approach using the chart suggested by Seed et al. (1984) a correction factorKσis applied to account for vertical effective overburden stresses larger than 1 tsf. Published data indicate a decrease inKσwith increased confining stress but with a wide range ofKσvalues for the same confining stresses, predicting significantly differing liquefaction resistance. The effect of confining stresses on liquefaction resistance was investigated as part of a comprehensive seismic assessment of Duncan Dam in British Columbia. The results indicate thatKσis dependent on confining stresses and the relative density of the soil, and values are generally significantly higher than much of the previously published data.Key words: liquefaction, sand, confining stress, density, cyclic resistance ratio.

ISSN:0008-3674    

DOI:10.1139/t94-006

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Values of small-strain shear modulusGmax, for a Champlain Sea clay deposit were obtained both under an embankment built 18 years ago, and outside of the area influenced by this embankment. The small-strain shear moduliGmaxwere measured in the laboratory by using resonant column tests and in the field by spectral analysis of surface waves. In addition to verifying the two methods, comparison of the in situ and laboratory values allowed evaluation of the influence of the sampling and the need to correct the laboratory values to account for the age of the deposit. The test program also made it possible to verify the influence of the deposit's consolidation and the existing models predicting small-strain shear moduli in clay deposits.Key words: shear modulus, shear-wave velocity, resonant column, in situ test, surface waves, soft clay.

ISSN:0008-3674    

DOI:10.1139/t94-007

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Traditionally pressuremeter tests results are interpreted using only the loading pressure–expansion data. An interpretation method has been developed that makes use of both the loading and unloading portions of a pressuremeter test and incorporates nonlinear, undrained soil behaviour. This method has been modified to handle large trains. The proposed interpretation accepts that some level of soil disturbance exists during the early stages of a pressuremeter test, and hence more emphasis is placed on the unloading portion of the test. A methodology is described to allow this interpretation procedure to be applied to self-bored, prebored, and full-displacement undrained pressuremeter tests. The proposed method is evaluated using self-boring and full-displacement pressuremeter test results from various published field projects. The interpretation is accomplished using commercially available microcomputer software that can perform the curve-matching process for both loading and unloading portions of the test.Key words: pressuremeter, loading data, unloading data.

ISSN:0008-3674    

DOI:10.1139/t94-008

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The paper describes a programme of field experiments with heavily instrumented displacement piles installed in a stiff, lodgement till. Measurements of the effective stresses recorded at various levels along the pile shaft during installation, equalization, and load testing are presented. Shaft capacity is shown to be governed by an effective stress failure criterion, with the mobilized stresses depending on the clay consistency, distance from the pile tip, shaft surface texture, type of loading, installation rate, and degree of equalization.Key words: displacement pile, instrumentation, glacial till.

ISSN:0008-3674    

DOI:10.1139/t94-009

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A numerical technique that couples the distinct-element and boundary-element methods was developed to simulate a granular soil deposit as a two-dimensional, circular disk assembly. A series of simulated penetration tests of a 60° apex angle cone was performed in normally consolidated and overconsolidated disk assemblies. The simulations allowed the cone penetration mechanisms to be evaluated from microscopic as well as the conventional, continuum mechanics points of view. Results show that the soil loading history can affect the characteristics of the soil failure mechanism and dilatancy. Lateral stress measurement behind the cone base is not sensitive to soil loading history. Finer particles appear to experience higher contact stresses and hence are more likely to be crushed by the cone penetration.Key words: cone penetration, sand, shear strength, loading history, distinct-element method.

ISSN:0008-3674    

DOI:10.1139/t94-010

出版商:NRC Research Press    

年代:1994

数据来源: NRC