In order to investigate the deformation and strength characteristics of reinforced sand, a series of relatively large-inscale direct shear tests was performed. Phosphor bronze strips and sheets with different configurations were used as reinforcement to study the effects of the shape and dimensions of reinforcement. Constant pressure tests and constant volume tests were conducted with different forms of reinforcement and different values of stiffness, surface area, spatial dispersion and surface friction. Test results show that for a given amount of reinforcement material, the reinforcing efficiency is higher with reinforcement having a larger surface area, a rougher surface texture and a larger degree of dispersion. The dilatancy at the residual state depends on the reinforcement property and geometry, and it is larger in more effectively reinforced sand with a larger shear zone. More dilative characteristics of reinforced soil results in larger shear strength under constant volume conditions at large strains.

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Various constitutive models for the description of time-dependent deformation behavior have been proposed. However, it is first verified in this article that a pertinent model applicable to the description of deformation for a wide range of stress below and over the elastic limit, i.e. the yield stress, has not been found up to the present. It should be noted that a stress goes out over the yield surface at a high rate of deformation, only elastic deformation being induced. The subloading surface model does not premise that a stress exists on the yield surface even in the plastic loading process and thus describes the plastic deformation induced by the rate of stress within the yield surface, exhibiting the smooth elastic-plastic transition. In this article the subloading surface model is extended so as to describe the time-dependence for a wide range of deformation rates by allowing the stress to go out from the yield surface based on the physical interpretation that a plastic deformation due to the mutual slip between microstructures is suppressed for the deformation at a high rate causing the increase of viscous resistance acting between the microstructures. Further, based on this, a time-dependent elastoplastic constitutive equation of soils is formulated by incorporating the secondary-consolidation phenomenon, and its ability to predict deformation behavior of soils is verified by comparisons with test data on fundamental time-dependent behavior with various deformation rates, creep and stress relaxation under the undrained condition.

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Particulate materials (consisting of solid structural units in mutual contacts) are highly dissipative media. Under some circumstances they display a collapsible behaviour. Two kinds of collapse are distinguished by the author : branching-off collapse (kinking of a constitutive function) and break-down (discontinuity of a constitutive function). They are illustrated via tests with a granulated clay. With every collapse the soil structure is rebuilt, and this is especially true for break-down. It is documented, by some experimental examples, that break-down, is contrast to branchingoff collapse, takes the form of a diffusion process.

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The Deep Mixing Method (DMM), a deep in-situ stabilization technique using cement and/or lime as a stabilizing agent, is often applied to improve soft soils. Among several improvement patterns, the group column type has been extensively used to treat subsoil of lightweight structures. A series of centrifuge model tests was performed to investigate the effects of external load condition and column strength on the failure behavior of the columns and the improved ground. The model foundations with different column strength were subjected to various combinations of vertical and horizontal loads in a 30 g acceleration field in order to establish failure envelopes in a vertical-horizontal loading plane. The tests show that the column type DMM improved ground failure involves either rupture or collapse of columns, depending on the loading condition and the column strength. It is also found that each column shows shear or bending failure depending on its location and the loading condition in the case of rupture breaking failure. The experimental data are compared with FEM calculations to determine the failure envelopes. The paper describes the failure envelopes for various failure patterns as well as the model test procedure.

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Sample quality was studied at three sites ; Ariake (Japan), Bothkennar (Britain) and Drammen (Norway), using various types of samplers. It was found that the unconfined compression strength (q_u) is significantly affected by the sample quality. Sample quality obtained by the Japanese standard (JPN) sampler is the same as that by the Laval or the Sherbrooke samplers, which have a worldwide reputation for their ability to get high quality samples. However, there is a remarkable difference in q_u for the lean clay layer of the Drammen clay between the JPN and the Sherbrooke samplers. It is concluded from a series of soil investigations that the reduction of the q_u value may be caused by two different reasons : loss of the residual effective stress and destruction of the soil structure. In most of the previous studies, these two phenomena were thought to take place concurrently. When the structure is kept unchanged and only the residual effective stress is lost, the recompression technique, where a specimen is consolidated under the same stress level as in situ, is effective in producing the in situ soil behavior. However, if the soil structure is destroyed and its e-log p curve is different from the original one, the recompression technique is not capable of providing real soil behavior.

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The effects of large displacement and deformation of liquefied subsoil during earthquakes have been seriously discussed in recent years. Although mitigative measures to prevent the onset of liquefaction are desirable, it is important from an economical viewpoint that there is a level of allowable displacement and deformation below which the induced ground movement does not cause serious problems to concerned facilities. That deformation is also acceptable that can be repaired within a reasonably short period of time. The present paper briefly examines the recent experience of a river dike during the 1995 Kobe earthquake and suggests that several measures, inclusive of an embedded sheet pile wall, are able to mitigate the displacement to an acceptable level. Then the study presents the results of small shaking table tests in which displacement of a liquefied slope was mitigated by an embedded wall made of either a sheet pile or compacted sand. The study proceeds to the development of an analytical method by which the mitigative effects of embedded walls are evaluated. The proposed method is so simple that a closed-form solution is available for simplified situations. Example studies were made of several situations.

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Field data indicate that the P-wave velocity in sand or gravel is sometimes much lower than that of water, even if the soil is below the water table. It is well understood that a slight decrease in saturation normally evaluated by the B-value has a significant effect on undrained shear behavior like liquefaction of saturated soil. In the first part of this research, theoretical formulations of the B-value, P-wave velocity and Poisson's ratio are made by taking into account the decrease in bulk modulus of water due to a mixture of air bubbles. Then, computations are carried out using formulas based on the soil properties of a typical sand or gravelly soils and Masa soil from the Kobe area to make charts correlating the variables. These charts indicate that a small decrement in the B-value in the interval of B=1.0 to 0.8 will considerably decrease the P-wave velocity. Thus, the P-wave velocity which is easily measured in the field can serve as a convenient index to quantitatively evaluate the insitu soil B-value.

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The flow deformation or strain softening in undrained shear of saturated sand is discussed in this paper. When evaluating the flow of field deposits, the prime issue to be addressed is whether the soil in its in-situ state has the potential to develop flow deformation or not. This paper presents a rational method which allows for such an assessment to be made and aims at quantifying the effects of grain-size distribution on the flow potential of sandy soils. On the basis of existing laboratory and field test results on sandy soils, a flow potential formulation was developed within the framework of the state concept. Here, the SPT blow count was used as a parameter for field characterization of sand deposits whereas the void ratio range (e_max-e_min) was employed as a measure indicative of the grading properties of sandy soils. It is shown that sands with a large value of void ratio range have a high flow potential, indicating that fines-containing sands are more susceptible to flow than clean sands. Results of this study also suggest that flow with zero residual strength is limited to field deposits with a very low SPT blow count, and that soils with a void ratio range of less than 0.35, such as coarse sands and gravels, are practically safe against flow with zero residual strength.

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The filtration compatibility of soil-geotextile systems has been assessed experimentally in the laboratory with the gradient-ratio test. A nonwoven geotextile was used against a variety of model soils that were prepared from glass beads. They exhibited a range of fines content, in both gap-graded and broadly-graded size distributions. Filter blinding and clogging, if it happens, occurs within hours of initiating unidirectional flow. The zone of soil above the geotextile that is influenced is relatively thin. In gap-graded soils, the movement of fine particles appears to occur at a conditioh of D₈₅/D₁₅>8. A new dimensionless index is proposed to quantify the internal stability of gap-graded soils.

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The small strain stiffness and anisotropic nature of two sands with different geological origin have been determined via laboratory seismic tests performed in a triaxial cell. Dry triaxial reconstituted specimens of Ticino river silica sand (TS) and of Kenya carbonatic sand (KS) were subjected to isotropic and anisotropic states of effective stress ; then both shear and constrained compression waves were propagated in vertical, horizontal and oblique directions by means of five couples of piezoelectric transducers especially arranged in the specimens. The propagated compression and shear waves allow the assessment of the constrained M₀ and shear G₀ moduli respectively, at very small strains where, as a first approximation many soils can be assumed, from an engineering point of view, to behave as an elastic cross-anisotropic medium with a vertical axis of symmetry. This paper, after a brief description of the novel measuring technique adopted and of the tested materials, summarises the test results and their interpretation in order to separate the effects of the fabric anisotropy from those produced by the state of effective stresses on soil stiffness. The stiffness and anisotropic response of the two tested sands are compared. Finally the results enable us to establish five independent constants of the cross-anisotropic elasticity model, which appears to be appropriate to reproduce the behaviour at small strain of the two sands.

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A friction pile-box foundation for the support of an urban bridge in Mexico City was instrumented. The goal was to record the foundation state variables to better our knowledge of the performance of this type of foundation under static and dynamic loading. Soil-raft contact pressures, loads on selected piles, and pore water pressures in the subsoil below the foundation have been monitored from the beginning of the foundation construction until now, two and a half years after the bridge was opened to traffic. During this period, the response of the soil-foundation system was recorded during the occurrence of two seismic events in 1997. This case history yielded valuable information about the foundation performance before, during and after seismic events, regarding the analysis, design and regulations for this kind of foundation. Pile-soil-slab load sharing mechanisms are devised from these records.

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The continuity and smoothness conditions and the loading criterion are the most fundamental elements in constitutive equations for reversible/irreversible deformation, which have been defined and formulated by the author (Hashiguchi, 1993a, b, 1994). In this article the continuity and smoothness conditions are reviewed in detail. Further, the loading criterion for plastic stretching in the constitutive equation with the plastic potential surface is derived from the requirement that the proportionality factor in the plastic potential flow rule is positive ; this would generally be applicable even to constitutive equations for the description of time-dependent elastoplastic deformation. In addition, the defects caused by the violation of continuity and smoothness conditions are verified illustrating unrealistic deformation behaviors predicted by the conventional and well-known cyclic plasticity models.

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