摘要:

A model introduced in the present paper is capable of describing the mechanical behaviour of anisotropically consolidated cohesive soils reasonably well. The salient features of the proposed model are summarized as follows: (i) generalized forms of the Cambridge models are given to both yield function and plastic potential; (ii) a combination of isotropic and kinematic hardening is used; (iii) a nonassociated-flow rule is proposed; (iv) the isotropic hardening involves plastic work not only related to volumetric change but also to deviatoric deformation; (v) the translation of the yield surface is specified by extending Ziegler's rule of kinematic hardening; (vi) the constitutive model has versatility and flexibility to describe expansion, translation, and rotation of a yield surface in stress space. Several undrained triaxial tests of anisotropically consolidated cohesive soils are simulated, and good agreement is observed between simulation and experimental data.Key words: anisotropy, dilatancy, cohesive soil, consolidated undrained shear, constitutive equation, stress-strain curve, pore pressure - strain curve, effective-stress path.

ISSN:0008-3674    

DOI:10.1139/t91-001

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A model of a pile–soil system subjected to vertical cyclic loading is proposed. The model is based on the classicalt–zconcept and on the compaction theory of granular materials to study the reduction of shearing resistance around a shaft owing to cyclic loading and the redistribution of loads carried by the shaft and tip of a pile. The model is applied to predict the behaviour of cyclically loaded piles in experimental conditions. Theoretical predictions against experimental data are presented. The model gives realistic predictions from a qualitative view point. Quantitative agreement is obtained for large-scale tests.Key words: piles, theoretical model, cyclic loading, compaction theory, redistribution of load transfer.

ISSN:0008-3674    

DOI:10.1139/t91-002

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The preliminary results of a study using mercury-intrusion porosimetry on freeze-dried samples of clayey soils are presented. The amount of secondary consolidation has been varied for several samples of three soil types by holding the consolidation stress steady at 120 kPa for different durations. Examination of the pore size distribution curves reveals that secondary consolidation cannot be due solely to the deformation of micropores. The relative degree of change in total, free and entrapped porosity appears to be related to the proportion of each initially in the sample.Key words: clays, consolidation, compressibility, fabric-structure of soils, secondary compression.

ISSN:0008-3674    

DOI:10.1139/t91-003

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A three-dimensional (3D) elastoplastic finite-element analysis, which is capable of simulating the advance of a tunnelling shield and the associated ground losses resulting from the tunnelling process, is used to calculate the deformations caused by the excavation of the Thunder Bay sewer tunnel. The soil parameters adopted in the analysis were based on the results determined from stress-dependent triaxial tests. The results of this analysis are compared with the measured soil displacements. Reasonable agreement between the calculated and observed 3D settlement distribution and horizontal displacements at different distances from the tunnel face is reported. This overall agreement for displacements under 3D conditions suggests that the method of analysis may be applicable to design problems involving tunnelling in soft clays similar to that at the Thunder Bay sewer tunnel provided that the soil parameters are reliably determined.Key words: tunnelling, three-dimensional analysis, finite element, elastoplastic displacements, ground deformations, Thunder Bay tunnel.

ISSN:0008-3674    

DOI:10.1139/t91-004

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The thermal consolidation by heating of an unsaturated silty soil is studied by means of six tests performed in a thermal triaxial apparatus. The results show the importance of the temperature parameter and a clear similarity with the classical consolidation tests on saturated soils. A constitutive law is proposed for the thermal consolidation by heat that allows the definition of indices of thermal compression. This law is used to calculate the displacements in an unsaturated fill for heat storing.Key words: unsaturated soil, consolidation, heat, triaxial, modelling. [Translated by the Journal]

ISSN:0008-3674    

DOI:10.1139/t91-005

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The softening process as observed in fissured, overconsolidated clays and mudstones is discussed in detail. Softening is classified into internal and external processes. The effect of softening is to decrease the shear strength of a material and its dilatant characteristics. This shear strength reduction is represented as a lowering of the failure envelope and a reduction in the degree of nonlinearity at low stress levels. There are some restrictions related to stress paths that affect the initiation of softening. The softening process may be formulated in terms of a time-dependent yield surface, and the finite-element method can be extended to analyze softening effects. A cut slope is analyzed as an example. The development with time of deformations is traced up to the collapse of the slope. This example contains the essentials to portray the role of the mechanism of softening. A distinction can be made between time-dependent deformation due to softening and those associated with conventional creep mechanisms.Key words: softening, time-dependent strength reduction, finite-element analysis.

ISSN:0008-3674    

DOI:10.1139/t91-006

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A comprehensive experimental investigation on the electroosmotic strengthening of soft sensitive clay was performed to assess the effectiveness of the treatment and to study the mechanism of the process. A specially designed electroosmotic cell was developed to prevent gas accumulation near the electrodes, to allow better electrode-soil contact, and to improve the treatment efficiency. This apparatus also enables the monitoring of the generated negative pore-water pressure along the sample length, settlement, voltage distribution, and current variation during treatment. The investigation covered two different types of soil trimmed at different orientations: the vertically and horizontally trimmed overconsolidated Wallaceburg clay and the vertically trimmed slightly overconsolidated soft sensitive Gloucester (Leda) clay. Results of this study showed that the voltage distribution and induced negative pore pressure at equilibrium along the sample are linear with steady current flow across the sample, indicating that the electrode design in the electroosmosis test apparatus is efficient. The electroosmotic consolidation curve is similar to that of the conventional consolidation curve, and the preconsolidation pressure was increased by 51–88% with an applied voltage up to 6 V. The undrained shear strength increased to a maximum of 172%, and the moisture content decreased by 30%. The technique of electrode reversal is employed, and a relatively uniform strength increase between the electrodes is observed.Key words: electroosmosis, electroosmotic cell, soft sensitive clay, negative pore-water pressure, preconsolidation pressure, stress–strain behaviour.

ISSN:0008-3674    

DOI:10.1139/t91-007

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A field test was undertaken to assess the effectiveness of electroosmosis in strengthening the soft sensitive (Leda) clay at the Gloucester test fill site. Specially designed copper electrodes were installed to prevent gas accumulation around the electrode and to allow pore water in the soil to flow out from the cathode without pumping. The variation of settlement, shear strength, and voltage distribution during treatment was measured, and tube samples were recovered before and after treatment for laboratory tests. The results of field vane tests at different locations within the treated area and at different times indicate that the undrained shear strength increased uniformly by approximately 50% for a period of 32 days throughout the depth of the electrodes. Concurrently, an average surface settlement of 50 mm was achieved. The total power consumption was less than 1% of the total project cost, indicating that the design of the treatment system was efficient. It is evident, therefore, that substantial increase in strength as well as general improvement in soil properties may be achieved by this improved version of electroosmosis. The elimination of pumping improved the economy of the process considerably. It is hoped that the process may receive wider application as a result of these improvements.Key words: electroosmosis, electrode, polarity reversal, Gloucester test fill, soft sensitive clay, uniformity of treatment, power consumption.

ISSN:0008-3674    

DOI:10.1139/t91-008

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Presentin situchemical treatment technologies for mitigation of petroleum hydrocarbon contamination are in the developmental stage or being tested. To devise efficient strategies for restricting the movement of petroleum hydrocarbon (PHC) molecules in the contaminated soil, it is proposed to utilize the sorption–interaction relationships between the petroleum contaminants and the soil substrate. The basic questions addressed in this paper are as follows (i) What are the prominent chemical constituents of the various petroleum fractions that interact with the soil substrate? (ii) What are the functional groups of a soil that interact with the contaminants? (iii) What are the bonding mechanisms possible between the soil functional groups and the PHC contaminants? (iv) What are the consequent changes brought about the soil physical properties on interaction with PHC's? (v) What are the factors influencing the interactions between PHC molecules and clay particles of the soil substrate? (vi) What is the possibility of improving the soil's attenuation ability for PHC's? The development of answers to the basic questions reveal that petroleum hydrocarbons comprise a mixture of nonpolar alkanes and aromatic and polycyclic hydrocarbons, that have limited solubility in water. The bonding mechanism between the nonpolar PHC's and the clay surface is by way of van der Waals attraction. The adsorption of the nonpolar hydrocarbons by the clay surface occurs only when their (i.e., the hydrocarbon molecules) solubility in water is exceeded and the hydrocarbons exist in the micellar form. Dilute solutions of hydrocarbons in water, i.e., concentrations of hydrocarbons at or below the solubility limit, have no effect on the hydraulic conductivity of clay soils. Permeation with pure hydrocarbons invariably influences the clay hydraulic conductivity. To improve the attenuation ability of soils towards PHC's, it is proposed to coat the soil surface with "ultra" heavy organic polymers. Adsorption of organic polymers by the clay surface may change the surface properties of the soil from highly hydrophilic (having affinity for water molecules) to organophilic (having affinity for organic molecules). The organic polymers attached to the clay surface are expected to attenuate the PHC molecules by van der Waals attraction, by hydrogen bonding, and also by adsorption into interlayer space in the case of soils containing swelling clays.Key words: petroleum hydrocarbons (PHC's), bonding mechanisms, functional groups, PHC-soil interaction, permeation, hydraulic conductivity, attenuation, van der Waals, organic polymers, organophilic.

ISSN:0008-3674    

DOI:10.1139/t91-009

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

This paper presents the analysis of an embankment failure over a soft clay deposit in the district of Caju, Rio de Janeiro. The uncommon feature of the analysis is related to the embankment's material, which is mainly composed of dumped sanitary and rubble fill, and the unconsolidated state of the subjacent clay layer. Index tests were performed to obtain geotechnical characteristics and a profile of the soft clay deposit, which were compared with a well-known Brazilian clay from the same area (Guanabara Bay). Oedometer tests,in situand laboratory vane tests, standard penetration tests, and conventional triaxial tests were also carried out. Total stress calculations were used to interpret and back analyze the failure and also to obtain the mobilized shear strength at both the fill and clay foundation. It was concluded that for an embankment cohesion of 0–20 kPa, the ratio between the back-analyzedCuand thein situpostfailureCuhas a magnitude similar to the soft clay sensitivity.Key words: case history, sanitary fill, soft clay.

ISSN:0008-3674    

DOI:10.1139/t91-010

出版商:NRC Research Press    

年代:1991

数据来源: NRC