This study concerns the development of residual deformations in soil subjected to static shear and cyclic stress components. This problem plays an important role in such situation as natural slopes, slopes of embankments and dams, quay walls. Among them, the present study focuses in particular on cyclic undrained behavior with static shear stress. Furthermore, in the case of structures with static shear stress and subjected to the earthquake shaking, the forces acting in the shear plane are generally one-way cyclic loading without reversing its direction. Experimental research was focused on the accumulation of shear strain in the soil element during one-way cyclic loading (torsional stress loading only on positive or negative side). Series of torsional shear tests on hollow cylindrical specimens of Toyoura sand with relative density of 40% and 60%, with isotropic stress condition under effective pressure of 98 kPa, 196 kPa and 294 kPa as well as anisotropic conditions were made in order to investigate the incremental shear strain per cycle during cyclic loading. The level of static shear stress was set equal to half of the ultimate stress under drained conditions (factor of safety equal to two). The experimental results showed that the presence of static shear stress increases the resistance of sandy soil. The experimental results of the shear strain increment per cycle and the number of cycles were plotted in a logarithmic scale to show a linear relationship with each other. Based on these findings a simple model for prediction of shear strain was developed.

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Centrifuge model tests have been conducted to investigate the effect of negative skin friction on piles installed through soft clay and founded in underlying dense sand. The first test series involved the study of fundamental mechanism of piles subject to negative skin friction only. In these tests, negative skin friction was induced by self-weight consolidation of clay followed by in-flight sand surcharge placement on the clay. The second test series examined the behavior of piles subject to simultaneous negative skin friction and axial load. The effects of axial load on the load-transfer characteristics along a pile experiencing locked-in negative skin friction induced by consolidating clay are investigated in detail in this paper. The effects of pile tip condition (end-bearing or socket pile), pile socket length and magnitude of applied load on the pile are also studied.

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This paper presents two kinds of constitutive model applicable for geosynthetic interfaces, namely a combined model (MODEL 1) and DSC model (MODEL 2). In order to verify the performance of the two models, back-predictions were carried out on smooth geomembrane (S-GM) and textured geomembrane (T-GM) interfaces with geotextile (GT), namely S-GM/GT and T-GM/GT interface using the parameters obtained from test results. For the combined model (MODEL 1), the total stress field is divided into two regions, i.e. pre-peak and post-peak region, to take into account the displacement-softening effect on the interface shear behavior. The DSC model (MODEL 2) was also considered to model the interface shear behavior between geosynthetics. This model is comprised of two reference states, namely the relative intact (RI) and the fully adjusted (FA) state, and one function, namely the disturbance function. Though the comparisons between measured data and back-prediction results for MODEL 1 and MODEL 2 (DSC model) showed good agreements with each other, MODEL 1 has a critical limitation related to the boundary value problem as it is inconvenient to implement'this model into FEM. Finally, DSC model (MODEL 2) was suggested as an appropriate model for simulating large-displacement shear behaviors with the characteristics of plasticity because the DSC model has been widely implemented in FEM process by many researchers.

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Soil samples were recovered from the Osaka basin, where Holocene as well as Pleistocene marine clays are thickly deposited. It is found from X-ray diffraction analysis that the component of clay minerals for these clay layers is almost identical through all depths. This fact suggests that the origin of these sediments has not been drastically changed through at least more than 1, 000, 000 years. Using data obtained by oedometer tests, this paper examines ageing effects on consolidation properties. It is found that void ratio for the Pleistocene clays keeps large even under high in situ effective overburden pressure (p'_vo). Salinity of pore fluid decreases with depth and becomes nearly zero at depths deeper than 70 m. However, the change in salinity does not give any influences on the index properties, suggesting that the relatively large void ratio for the Pleistocene clays is caused by other reasons than leaching. It is also found that the Pleistocene clays reveal no particular differences in consolidation properties, but fundamentally similar to those of Holocene clays. There is no distinguished difference in the overconsolidation ratio (OCR), non-linearity of the e-log p' relation after yield consolidation pressure including the maximum compression index (C_cmax) and the hydraulic conductivity (k). The only prominent difference in the Osaka Pleistocene clays, compared to the Holocene clay, is relatively small void ratio due to the large p'_vo.

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Air-foam treated lightweight geo-material (LGM), which is a mixture of dredged clay, cement, and air-foam, has been developed and utilized for various coastal structures, in order to reduce both overburden stress acting on an underground structure (tunnel, buried pipe, etc.) and lateral earth pressure acting on a retaining structure (quay wall, seawall, shore protection, etc.). In this study, one-dimensional compression behavior of the LGM was investigated in microscopic point of view with scanning electron microscope, optical CCD digital microscope, color laser 3-D profile microscope and mercury intrusion porosimetry (MIP). Though air-foam bubbles with diameters in a range of 200-500 μm are observed in the microscopic images, these sizes are not well reflected in the pore entrance size distribution by MIP because of the very small pore entrances. In MIP, there are in total three pore groups for LGM as in ranges of greater than 10 μm, 0.5-10 μm, and less than 0.5 μm. The group of the largest size corresponds to the air-foam bubbles, the one of the smallest size corresponds to the intra-pores in aggregates, and the one of the middle size corresponds to the inter-pores between the particle aggregates. When compression pressure increases, the observable air-foam bubbles primarily decreases; then the inter-pores between aggregates slightly decreases under a large compression pressure, but the intra-pores in aggregates do not decrease so much.

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Consolidation settlement of two Holocene marine clays improved by prefabricated vertical drain is analyzed in order to investigate the applicability of Constant Rate of Strain consolidation test by using the stress-strain relations determined by the test carried out at a strain rate of 0.02%/min. The clay deposits, found at Yokohama, Japan and Banjarmasin, Indonesia, are slightly to moderately overconsolidated. Since the final stresses inside the ground due to construction works are close to consolidation yielding stresses, settlement behavior of the clays is analyzed by considering their state of overconsolidation. Moreover, because the compressibility of clays significantly changes during the conversion from overconsolidated state to normally consolidated state, the analysis considers non-linearity in stress-strain relations. It is confirmed, from the comparison between the actual settlement and the result of the analysis, that Constant Rate of Strain consolidation test can be applied directly to detect the stress-strain relations mobilized in the field when clay deposit improved by vertical drain is concerned.

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A series of triaxial compression (TC) tests were performed on Toyoura sand to evaluate the viscous effects on the stress-strain behaviour following the shear yielding mechanism. It is shown that very different shear stress and shear strain relations obtained from TC tests performed along different stress paths become rather unique when converted into relationships between the stress parameter X^t_s=(q/p_a)/(p' /p_a)^βf_s, which is deemed to control the shear yield mechanism, and the normalized irreversible shear strain energy k_s, which is the stress path-independent strain hardening parameter for shear yielding. Along each inviscid yield locus quantified based on the test results, with an increase in the effective mean principal stress p', the deviator stress q increases at a relatively large rate while the stress ratio q/p' decreases at a relatively small rate. According to the non-linear three-component model described in the paper, the stress parameter X^t_s is decomposed into the inviscid and viscous components, X^f_s and X^v_s. The inviscid shear yield loci are described in terms of X^f_s and develop with an increase in k_s. The viscosity function g_v(k_s) is introduced to relate X^v_s to X^f_s in the form of X^v_s=X^f_s-g_v(k_s) based on the test results. It is shown that the viscous effects on the X^t_s-k_s relations obtained from the TC tests performed along a wide variety of stress path could be simulated rather well by the model taking into account the decay of the viscous component X^v_s with an increase in k_s.

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The effect of pore pressure response around a pile onp-y behavior, defined as the relation between subgrade reaction and relative displacement between soil and pile, is examined based on large shaking table tests conducted on pile-structure systems constructed in liquefiable soil deposits. Relative displacement between soil and pile during liquefaction alternatively creates extension stress state on one side and compression stress state on the other side of the pile. The pore pressure and earth pressure on the extension side decrease significantly, while those on the compression side maintain almost constant or increase slightly. The large reduction in pore pressure and earth pressure on the extension side is caused probably by the combined effect of extension stress and dilation induced by shear stress. The insignificant change in pore pressure and earth pressure on the compression side, in contrast, is probably due to the adverse effect of compression stress and dilation induced by shear stress. As a result, the horizontal subgrade reaction of the pile increases in such a way that the pile is pulled by the soil on the extension side. Such mechanism is completely different from that occurring in dry sand where horizontal subgrade reaction is always induced by the increase in earth pressure on the compression side. The reduction in pore pressure and earth pressure on the extension side becomes smaller in the soil inside than outside the pile group. This is probably because, inside the pile group, the extension stress induced by a pile on one side may be canceled by the compression stress induced by a pile on the other side, leading to an insignificant reduction in pore pressure.

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The pH and Eh effects on the mobility of zinc within landfill clay liner are investigated by modified batch tests on Osaka marine clay with cultivation of native microorganisms in the soil. The long-term mobility of zinc in landfill clay liner is discussed based on the pH buffering capacity of liner soil-leachate system. Tests results show that both pH and Eh conditions control the mobility of zinc in Osaka marine clay. Low redox potentials and neutral to basic pH conditions in landfill sites tend to prompt the insolubilization of zinc in landfill liner, in particular in the case where marine clay is used to serve as a natural liner material at offshore landfill sites. In the long-term perspective, oxygen will intrude finally into the landfill, which switches the anaerobic decomposition into an aerobic one and results a decrease in pH. Titration test results indicate that the newly generated leachate has a higher acid buffering capacity than the aged leachate, while leachates from MSW incineration ash have high hydroxides alkalinity at pH>8. Test results reveal that both of the wastes and clay liner possess enough acid buffering capacity to consume the protons produced in organic oxidation reactions. Therefore, high levels of remobilization of heavy metals are not expected in the long-term perspective.

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A new unified formulation of two dimensional limit equilibrium slope stability analysis method is developed in this paper. Based on the present formulation, Bishop's simplified Method, Janbu's simplified and rigorous methods, Lowe and Karafiath's method, Corps of Engineer's Method, Load transfer factor method, Blocking equilibrium Method, Spencer's Method and Morgenstern-Price's method and Leshchinsky's method can all be derived as a special case of the more general formulation. The authors have also investigated into several interesting examples in the determination of factor of safety. To solve for the factor of safety under difficult problem, Gauss-Newton method with a line search step selection strategy is proposed.

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