Landslides resulting from rain and melting snow are generally known to be caused by an increase in the ground water level within the slopes. In these cases, an element on a slip surface before failure is subjected to the increase in pore water pressure, and deforms under a drained condition. It is very important, therefore, to estimate the drained deformation characteristics of clay during this increase in pore pressure. A drained test of cohesive soils, however, requires a long-term period to complete, and the drained deformation of cohesive soils during the decrease in mean effective stress has never been made clear. In this paper, deformation characteristics of a saturated cohesive soil subjected to the increase in pore water pressure were investigated and were compared with its undrained deformation characteristics. State points (p', q) at which a given value of equivalent shear modulus Ge (=Δη/Δε_s, where ε_s is shear strain and η is stress ratio, q/p') is the same locate in the same very narrow zone for both of the two tests stated above. Any zone for an other Ge value locates in parallel with the other zones. Therefore, the Ge-value at a given stress state is independent of stress paths. Stress points showing the same ε_v-value forms a contour line in the pore pressure increase tests, and the line can be uniquely defined for a given ε_v-value. The distribution pattern of these lines is similar to the effective stress paths obtained from the consolidated undrained tests on overconsolidated specimens with different OCR-values. As a result, drained deformation characteristics in the pore pressure increase tests may be estimated with little error from the results of rapid undrained shear tests. In the final, to investigate the deformation behavior under general stress conditions, the effects of direction of principal stress and stress induced anisotropy on the above deformation characteristics were examined using the triaxial extension and torsional shear test results, and using the results on anisotropically consolidated specimens.

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A constitutive relationship, known as CARMEL, is proposed to predict the behaviour of anisotropically consolidated clay. Based on the principles of critical state soil mechanics the model has a non-associated flow rule and accommodates both isotropic and rotational strain hardening. A characteristic of the CARMEL model is that it can represent the changes in stress-strain behaviour of soil caused by variations in stress induced anisotropy. This permits the modelling of long stress paths, during which the induced anisotropy of the soil can be greatly changed. To assess the model, data from stress path triaxial tests reported in the literature have been predicted. Comparisons between the experimental data and predictions of CARMEL show good correlations which significantly improve on predictions using Modified Cam Clay, an isotropic associated model.

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This paper presents reinforcing mechanisms and a method for analyzing reinforced earth structures. The reinforcing mechanism presented is divided into two stages, a fixed slip surface and an arbitrarily selected slip surface. The mechanism is studied through direct shear tests and plane strain compression tests including some geotextiles. The reinforcing materials considered in this paper only have tensile strength. The authors have already proposed a method called Generalized Limit Equilibrium Method (GLEM) for analyzing stability problems. The validity of the method has already been shown in previously published papers. In this paper, the method is extended to carry out a stability analysis for reinforced earth structures. Finally, large scale model tests for the bearing capacity of foundations on reinforced slopes were carried out to investigate the validity of the proposed reinforcing mechanism and the analytical method. Through comparisons of observations of experiments and results of the analytical method, the validity of the present work is demonstrated.

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The use of vertical drains and surcharge to accelerate the consolidation of clayey soils is well established in soil improvement technology. For this method of soil treatment, it is important to monitor the progress of consolidation where the average degree of consolidation is usually defined as the ratio of current settlement to the ultimate settlement due to primary consolidation. An accurate estimate of the ultimate primary settlement is, therefore, required in order to determine the state of consolidation, and the appropriate time for surcharge removal when the desired degree of consolidation has been achieved. Recently, Tan (1995) proposed a new hyperbolic method to identify the 60% and the 90% consolidation stages from field settlement data due to one dimensional consolidation. Knowing the settlement at these points, it is possible to determine the ultimate primary settlement. Once sufficient data has been recorded to identify the linear portion of the hyperbolic plot between the 60% to 90% consolidation stages, the method can be employed. This method has been validated by application to various well documented case histories in the published literature. In Japan, however, Asaoka's method for estimating ultimate primary settlement from field observation has been widely used and is well accepted by the geotechnical engineering community. This research paper presents a comparison of two different observational methods for monitoring the progress of consolidation to determine their similarity and differences, and their accuracy of predictions compared to actual observations. First, the theoretical basis of the two methods are examined. It was found that settlement data beyond the 60% consolidation stage are needed in both methods to make accurate predictions of ultimate primary settlement. Next, both methods are applied to oedometer laboratory consolidation data for kaolin specimens in order to determine how prediction of ultimate primary settlement and coefficient of consolidation would compare in carefully controlled laboratory experiments. Finally, both methods are applied to several well documented case histories of vertical drain projects, and the predictions of ultimate primary settlement and in situ coefficient of consolidation are compared. It was found that both methods gave good agreement with predictions, making them complementary tools for use in monitoring consolidation in field applications.

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The Standard penetration test and the Swedish weight sounding test are both generally used on many railway lines. Since as these tests are relatively labour-intensive, however it is difficult to perform them at many locations on one site. At the same points on many railway embankments, both a Portable dynamic cone penetration test, which is light and portable, and the Swedish weight sounding test were made. Correlations in soil strength between these two tests were analyzed and a relationship was proposed for equations between N_C for the Portable dynamic cone penetration test and W_SW, N_SW for the Swedish weight sounding test. A conversion formula between N_C and N-value in the Standard penetration test or q_U for unconfined compression strength was also proposed.

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A numerical investigation was carried out to evaluate the effect of wall movement modes on static active earth pressure. Interface elements with bi-linear stress-displacement relation are newly developed and introduced between the backfill soil and the wall to simulate the frictional behavior. The conventional linkage elements have been idealized suitably to avoid separation between the wall and the soil during the active movement of the wall. The active state has been defined based on the progressive formation of a failure zone in the backfill. The tendency of the failure zone formation is seen to be governed by the modes of wall movement. The calculated active state parameters were compared with the parameters calculated using other methods based on rigid plastic assumptions. The resultant active thrusts and their points of application are found to be a function of the wall movement modes. Empirical equations containing wall movement mode as a governing parameter were derived for calculating the active earth pressure coefficient and the relative height of the resultant active thrust for various angles of internal friction of the backfill.

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The interaction between a penetrating shaft and the surrounding soil media under impact loading is a frequently encountered phenomenon in geotechnical engineering. Examples of such dynamic soil/shaft interaction would include dynamic pile driving, standard penetration testing (SPT), and dynamic driven rod test. Presented in this paper is a novel approach, based on the principle of dynamic system identification, which enables identification of dynamic soil-pile interaction model parameters. The analytical transfer function, relating the output stress wave forms to the input stress wave forms in the soil/shaft system, is derived using the Laplace and Fourier Transform techniques and the one-dimensional wave propagation theories. A numerical solution algorithm based on a variation of gradient method is coded into a micro-computer based program to solve the frequency-dependent soil-pile interaction parameters (Smith model) : soil damping and soil spring stiffness. To further reduce the amount of computational effort required in the solution of the frequency-dependent dynamic soil properties, it is suggested that the solution be obtained for the first-mode natural frequency of the measured stress waves. The results obtained from this simplified solution algorithm, when compared with both numerical simulations and controlled laboratory tests, are reasonably acceptable. The proposed parameter identification technique offers a viable alternative data interpretation procedure for deducing pertinent Smith model parameters used frequently in pile driving analysis.

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An important unresolved problem in geotechnical engineering practice is the determination of the shear strength of the soil obtained from a laboratory test for slope stability analysis. In certain cases, there are wide discrepancies between laboratory test results and the actual in-situ values of the shear strengths of soils. It is necessary, therefore, to develop laboratory procedures whereby a reliable result for engineering design can be obtained, and to determine shear strength values along slip surfaces relevant to different types of landslides. The emphasis of this study is to obtain relevant shear strength parameters for landslide clays from laboratory tests used in slope stability studies. This paper initially describes testing technique, preparation of sample and modification of the direct shear box apparatus during a series of tests. The shearing surfaces of landslide clays were then observed by using a scanning electron microscope to determine the influence of reversal shear on the clay particle reorientation and the difference in microstructure characteristics between the undisturbed samples and the remolded samples. The shear strengths from laboratory tests were compared with the computed values for typical landslides in Tertiary mudstone to confirm their reliability in slope stability analysis. The comparison of laboratory test results and computed results indicates that the residual strength parameters for the reversal direct shear box tests on the undisturbed samples should appropriately be used for evaluating slope stability, whereas the creep yield values agree with the computed ones for an initial slide in a non-fissured Tertiary mudstone.

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The critical state soil mechanics framework has been extended to include the effects of structure in natural soils. The porosity of these soils is considered to be a directional measure and its distribution is characterized by a functional form which is determined experimentally. The plastic energy dissipation formulations of the family of critical state soil models have been modified to account for fabric. New expressions for the state boundary surface and the yield locus of natural soils have been derived. The applicability of the concepts to model the yield of natural soils is illustrated. The collapse of the solid skeleton is evident prior to the initiation of strain-softening behavior for certain soils. It is shown that the behavior subsequent to collapse may be highly unstable depending on several factors including the rate of loading, the collapsiveness of solid skeleton, and drainage conditions.

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An undisturbed and high quality soil sample is necessary to investigate the mechanical behavior of a natural soft clay. Large intact soil samples must be prepared in order to carry out a torsional shear test or a truly triaxial compression test in geotechnical engineering practice. In this study, the applicability of a new Laval type sampler with 208 mm diameter designed based on the design principle proposed by the geotechnical group of Laval University, Canada is discussed. Laboratory tests on samples of typical Japanese sensitive soft clays obtained with a new Laval type sampler compared with samples taken with the Japanese piston sampler, the Shelby tube, NGI 54 mm sampler and ELE 100 mm (ELE-100) sampler were carried out to demonstrate the superiority of the Laval type sampler over the piston sampler. The quality of large samples obtained with a Laval type sampler was confirmed to be better than for samples obtained with other samplers.

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A rigid-plastic analysis of an assembly of regularly arranged circular elements with an equal diameter was made to consider the relationship between the micro- and macro-mechanisms of cohesive granular materials. No elastic constant for elements was employed whereas rolling and plastic sliding at the contact points was considered. The equations of equilibrium of elements at the critical state were solved by using the linear programming method to minimize the upper bound of the applied force. Some of the deformation modes were compared with the results of an experiment where a set of coins are used. It was found that the applied force at critical state can be obtained in a quasiclosed form by considering the condition of equilibrium of the whole assembly. Finally the global cohesion is related with the local one in a simple way when the number of elements are increasing.

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Sample disturbance was investigated in terms of the volumetric strain of an oedometer specimen, ε_υο, at in-situ effective overburden pressure, σ'_υο, determined from the 24-hour e-log σ'_υ curve. Unconfined compression and oedometer tests were performed on samples of natural deposits from ten different sites in Japan. The ε_υο value has a unique correlation with the plasticity index, I_p, σ'_υο, overconsolidation ratio, OCR, and degree of sample disturbance. The ε_υο values of the in-situ sample before intentional disturbance in the laboratory were in the range of 0.85% to 7.02%, and the average was 3.80%. The ε_υο values of the completely remolded sample were in the range of 7.52% to 23.07% and the average was 15.75%. The ε_υο value, resulting from intentional sample disturbance in the laboratory, is given as a function of the ratio of unconfined compressive strength, q_u, of sample disturbed in the laboratory to that of the in-situ sample. A procedure for obtaining values of strength and consolidation parameters of an in-situ soil, and a method for estimating the preconsolidation pressure, σ'_p, compression index, C_c, e-log σ'_υ curve, and coefficient of consolidation, c_υ, values for the in-situ soil are proposed from the I_p and the measured values of ε_υο, σ'_p, C_c, and c_υ for disturbed samples in the standard oedometer test.

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This paper provides a numerical analysis of the bearing capacity of a two-layered soil deposit : a crust on saturated soft clay. The surface crust is modeled as a Cosserat medium, considering couple stresses for the bending deformation, and the underlying clay layer is treated as an elasto-plastic material. The formulation of the Cosserat-FE for the two phase media is presented briefly, and a numerical comparison between the Cosserat and an ordinary continuum, for the example of a simple beam, demonstrates the effect of couple stresses. Asaoka's method allows us to predict the bearing capacity of such two-layered deposits by considering the settlement or horizontal deformation beneath the embankment. The numerical results are then discussed.

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