Hajime Matsuoka

Swelling characteristics of fractal-textured bentonite and its mixtures

Swelling deformation and swelling pressure tests of Tsukinuno bentonite and its mixtures with Toyoura sand were performed on a modified odometer. The swelling strain and swelling pressure of bentonite and its mixtures are dependent on the dry density, the increment of water content and the surface fractality of bentonite particle aggregates in voids. The water volume absorbed by bentonite is related to the surface fractal dimension (Ds) of bentonite. The correlation of the water volume to vertical overburden pressure (p) is obtained as Vw/Vm=Kp Ds� 3 for Tsukinuno bentonite with fractal-textured surface. The maximum swelling strain is predicted according to the correlation of the water volume to vertical overburden pressure. The predictions of the maximum swelling strain are in satisfactory agreement with the experimental data. Furthermore, the good relationship between swelling strain and elapsed time is also proposed in this paper. D 2003 Elsevier Science B.V. All rights reserved.

Collapse Behavior of Compacted Clays in Suction-Controlled Triaxial Tests

Using a suction-controlled triaxial apparatus for unsaturated soils, a series of tests on a compacted clay was performed to investigate the influences of stress states, water content, void ratio, and matric suction on the collapse behavior. The triaxial tests were carried out under the conditions of (1) different stress ratios and mean stresses, (2) triaxial compression and extension, (3) different initial void ratios of specimens with the same water content, (4) different initial water contents with the same degree of compaction, and (5) different controlled matric suctions. The main conclusions were obtained as follows: (1) The volume change induced by the collapse mainly depends on the initial void ratio and mean net stress under which the collapse occurs, irrespective of imposed matric suction; (2) the amount of collapse is small at both low and high confining stresses, and there exists a maximum value of collapse at a particular mean stress; (3) the shear strain increment induced by collapse depends on stress ratio, triaxial compression, or extension stress; (4) when imposed suction is decreased, large collapse deformation takes place in the samples compacted dry-of-optimum, while little collapse deformation takes place in the samples compacted wet-of-optimum; and (5) the collapse behavior can be explained by the elastoplastic theory for unsaturated soils.

DEVELOPMENT OF A NEW IN-SITU DIRECT SHEAR TEST

An in-situ direct shear test apparatus, in both small and large sizes, and its testing techniques have been developed. This test is performed simply by pulling horizontally a latticed shearing frame, embedded in the ground, with a flexible rope or chain under the application of a constant vertical load on the sample. In the new test, the real normal and shear stresses acting on the shear plane can be exactly measured. A number of the large-sized in-situ direct shear tests have been performed on 8 kinds of coarse-grained granular materials including rockfills at various construction sites of embankments. The measured shear strengths approximate those of large-sized triaxial compression tests on samples with parallel grain-size distributions. The smaller version of this new test has been used successfully for testing sands and clays. The extreme simplicity and high accuracy of this newly developed test are emphasized.

The SMP concept-based 3D constitutive models for geomaterials

1. Spatially Mobilized Plane (SMP) and SMP Criterion 2. Introduction to Cam-Clay Model 3. The Cam-Clay Model Revised by the SMP Criterion 4. Elastoplastic Constitutive Models for Geomaterials using Transformed Stress 5. Concluding Remarks

Generalization of a Constitutive Law from Frictional Materials to Cohesive Materials

A unified constitutive law, which is capable of modelling the behaviour of both cohesive material and frictional material, is formulated based on the concept of “Extended Spatially Mobilized Plane (Extended SMP)” with a parameter of “bonding stress σo”. The “Extended SMP” includes the SMP applicable to frictional materials such as granular materials (σo=0) and the octahedral plane applicable to cohesive materials such as metals (σo→∞) at the two extremities. This corresponds to the fact that the two extremities of frictional and cohesive materials are granular material and metal. The constitutive law is quantitatively verified by experimental data of triaxial compression and extension tests on a cement-treated sand.

A Constitutive Model for Granular Materials Evaluating Principal Stress Rotation

Summary A constitutive model for granular materials by which the general strain increments (de x , de y and dγ xy ) are directly related to the general stress increments (dσ x , dσ y and dτ xy ) is proposed. The stress-strain matrix between the strain increments and Ihe stress increments is expressed in general coordinates. In order to evaluate the influence of rotation of the principal stress axes on strains, “principal stress rotation tests”, in which the stress path is the circumference of a Mohrs circle, are carried out by a “two-dimensional general stress apparatus” using a stack of aluminium rods, and analyzed by the proposed model. The effect of discontinuous change in the principal stress direction is also considered from the fabric change of granular materials. The model is extended to a three-dimensional one.