This paper examines how geotechnical characteristics of soils can be influenced by the presence of diatom microfossils, using an artificially prepared mixture of soil and diatomite. Test results indicate that the presence of diatom microfossils substantially alters the index properties as well as other fundamental engineering behaviours of a soil, owing to the predominantly hollow structures of microfossil skeletons having rough and interlocking surfaces. For example, with the increase in diatomite content, compressibility and the internal friction angle of a soil increase. This study has also made an attempt to quantify the diatom microfossils present in natural soils.

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The relationship between the shapes of the yield surface and the undrained effective stress path (UESP) of loose sand is investigated for triaxial loading conditions. It is shown that the UESP can be used in the construction of capped yield surfaces for sands. The stress ratio M_p, measured at a point where the UESP of loose sand reaches a peak, has been incorporated as a material parameter in the analytical relationship by which the yield surface is defined. The variations of M_p with void ratio, state parameter, and consolidation stresses are examined and compared with previous studies, in cases where such studies exist. It is shown that M_p is strongly influenced by soil dilatancy and anisotropy and its variation is remarkably consistent with the variation of soil strength and yielding stresses. Quantitative relationships for the variations of M_p are then introduced; these have been used elsewhere in constructing yield surfaces and modeling the constitutive behavior of sands. In addition to their use in modeling sand behavior, the yield surfaces and quantitative variations of M_p obtained here can be used in quantitative assessments of the susceptibility of loose sandy soils to flow liquefaction.

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In very loose sand, the ratio M_p of shear stress to mean normal stress at the peak point of the undrained effective stress path (UESP) is very close to the stress ratio Mat the peak point of the capped yield surface. Stress ratios M_p can therefore be used in constructing yield surfaces of sands. These stress ratios have also been used in the past in evaluating flow potential of loose sand. Application of M_p for these purposes requires that factors affecting this stress ratio, and quantitative relationships for the variation of M_p with these factors be determined. In this paper, effects of the intermediate principal stress and direction of loading on M_p are investigated, and models are developed by which these effects can be quantified. It is shown that variations of M_p with these factors are similar to the variations of yielding stresses obtained from stress-strain data. Yield surfaces obtained from the variation of M_p indicated a strong dependency of yielding stresses on inherent anisotropy. Data examined in this paper also suggest that the effects of inherent anisotropy on yielding stresses are controlled primarily by the relative magnitudes of the normal stresses applied in the principal directions of material anisotropy.

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One-dimensional consolidation inverse analysis based on the stochastic nonlinear consolidation model (SNCM) is discussed in this study. The model is determined from the standard consolidation test results, and represents the non-linearity and spatial variability of the coefficient of volume compressibility and the coefficient of permeability simultaneously. Furthermore, the inverse analysis method is proposed on the basis of the SNCM and the finite element method mixed with the Monte Carlo simulation. Measured settlement and pore water pressure are used as observation data in the inverse analysis. The method is applied to the consolidation test results of kaolin clay, and its applicability is confirmed firstly. Then the inverse analysis of an actual soft ground is performed. Future consolidation behavior of the ground is predicted, and the spatial variability and the non-linearity of the consolidation parameters are identified. It is clarified in this study that complicated spatial variability and non-linearity of the consolidation parameters could be considered appropriately in the proposed inverse analysis method, and the method gives accurate prediction of consolidation behavior.

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Monotonic and cyclic loading tests have been carried out on a silica sand over a wide range of stresses in order to compare non-crushing and crushing behaviour. Samples were sieved at several stages of testing to theoretically determine the increase in particle surface area and hence degree of crushing. Undrained shear behaviour was compared for crushing and non-crushing regions above 3 MPa. Samples consolidated to 0.1 MPa demonstrated strong dilative behaviour, while above the yield stress of 3 MPa dilation was suppressed and considerable particle crushing occurred. Shearing caused a marked increase in particle crushing particularly after the phase transformation point. Crushing at the steady state was similar for isotropic and anisotropically consolidated sands. At high confining pressures the cyclic strength curves were similar to those for loose sands except for confining pressure dependency due to particle crushing. For low confining stresses cyclic strength increased with initial stress ratio, while for high confining stresses it decreased with initial shear stress ratio. In the cyclic tests there was no significant crushing for 0.1 MPa. Crushing was seen to increase rapidly after the phase transformation point, where high strains developed and where particle rotation and translation contributed to the crushing process.

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In a major earthquake, it is reasonable to assume that the mechanical behavior of a pile foundation and the surrounding ground is nonlinear. It is commonly accepted that the dynamic behavior of a group-pile foundation is not only related to its own mechanical properties, but also to the upper structure supported by the foundation, and to the surrounding ground. It is recommended, therefore, that a full system, which consists of superstructures, foundation and ground, be considered in the dynamic analysis because of the merit that relatively few assumptions are adopted. The most important thing in the dynamic analysis, however, is that the individual nonlinear behavior of soils and piles should be properly evaluated. In this paper, a new beam theory is proposed for a reinforced concrete material (RC material). The theory is based on a weak form in which the axial-force dependency in the nonlinear moment-curvature relation is considered. Its validity is verified by experimental results of an RC cantilever beam. Then, an elevated bridge with a 12-pile foundation is analyzed using a three-dimensional elastoplastic finite element analysis (DGPILE-3D). The piles are cast-in-place reinforced concrete and have a diameter of 1.2m. Meanwhile, the ground soil is simulated with a tij subloading model in which the concepts of kinematic hardening and subloading are adopted. The purpose of the paper is to provide an accurate numerical way of evaluating the dynamic behavior of a pile foundation during an earthquake.

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The objective of this paper is to evaluate both physical and mechanical properties of in-situ light weight soil with air foams using an industrial X-ray CT scanner. The specimen used in this study was in-situ SGM (Super Geo-Material) which was a light weight soil created by mixing dredged slurry with cement and air foam. This was sampled at the trial construction site of new Kumamoto seaport, Japan. Two different materials of air orientation which were surface active agent and protein were examined at the site. First of all, the effect of different kinds of air foams on the physical property of in-situ light weight soil was discussed using the results of CT scanning, in which the distributions of the density and air foams in the soil were taken into consideration. Furthermore, as a mechanical property, a series of unconfined compression tests was conducted for the in-situ specimen, and the density evolution was also investigated by scanning of the specimen during unconfined compression. Here, the effects of both distribution and size of air foams were also clarified. Finally, the effectiveness of the industrial X-ray CT scanner in geotechnical engineering was confirmed based on all these results.

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The simplest convex conical surface in the principal stress space is proposed in this article, relaxing the requirement that the frictional angles in the triaxial compression and extension states coincide with each other. It could be adopted as the equation of the critical state surface which is incorporated into the yield/loading surface in elastoplastic constitutive equations of soils. Also, it could roughly describe the failure surface of soils although the failure surface is not a material property, depending on loading conditions, i.e. the drained (volume change) or the undrained (constant volume), the constant lateral stress or the constant mean stress, etc.

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Landfill leachate is characterized by high organic compounds that can be used by microorganisms as nutrients and induce a series of redox reactions. Thus, redox potential as well as pH is considered to have an effect on the behavior of contaminants in leachate from landfill sites. Modified batch tests, cultivating the native microorganisms in soil specimens, were conducted to evaluate the bacteria-induced redox and pH effects on the natural attenuation mechanisms of heavy metal in the bottom clay liner of landfills. The marine clay sampled from Osaka Bay, Japan was used as a natural clay liner material due to the consideration that some of the solid waste landfill sites in Japan are located in coastal areas. Iron and zinc were selected as target pollutants. Test results show that both pH and redox potential indicated a combined effect on the solubility of zinc and iron. Under the denitrification and Fe(III) reduction conditions, zinc was soluble and its solubility was only controlled by pH. When pH increased higher than 7.2, zinc precipitated as hydroxides and adsorbed on soil particle surfaces. Under the sulfate reduction condition, the formation of zinc sulfides became another attenuation mechanism. Iron was insoluble under the aerobic and denitrification conditions in natural pH conditions. Elevated levels of soluble iron were observed in moderately reduced and highly reduced conditions. A combination of nearly neutral pH and extremely low redox potential condition in landfill site tends to promote the insolubilization of zinc but the solubilization of iron.

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