A high-pressure triaxial compression and extension apparatus was employed to investigate the effects of initial relative density on the drained behavior of sand. Experiments were performed on cylindrical specimens of Cambria sand with initial relative densities of 30% and 60%, and compared with previously published results for 90%. Confining pressures in the range of 0.25 to 60MPa were employed to obtain the characteristic behavior of the sand over a large range of pressures. As the confining pressure increased particle crushing increasingly influenced the stress-strain and volume change relations, producing increasing strains to failure and increasingly contractive volume changes. Beyond certain high values of mean normal stress at failure, increasing with initial relative density, the volumetric contraction and strains to failure began to decrease. The Mohr-Coulomb failure envelopes show the greatest curvature for the highest density, but the failure envelopes merge at high pressures where, due to particle crushing, the relations between void ratio and isotropic pressure are described by a single curve. The experiments show clearly that the rates of dilation at failure and the friction angles are directly related to each other, as has been proposed by many investigators. The friction angles are higher in extension than in compression for lower confining pressures, but a crossover occurs and the friction angles are higher in compression than in extension for higher confining pressures.

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A systematic investigation of the undrained behavior of sand at high pressures was performed to study the effects of initial relative density on the stress-strain, pore pressure, and strength behavior. Experiments were conducted on Cambria sand with initial relative densities of 30% and 60%, and the results are compared with previously published data for an initial relative density of 90%. Triaxial compression and extension tests were performed on cylindrical specimens with isotropic consolidation pressures in the range from 8 to 60MPa. Particle crushing played an important role in the observed behavior. Stress-strain, pore pressure, and strength behavior were found to be very similar and almost independent of initial relative density at high pressures, because the isotropic compression curves tend to merge once particle breakage becomes important at these high pressures. Effective stress friction angles for undrained compression and extension tests varied systematically in the range from 32° to 35° with slightly higher values for the compression tests. Interpretation of all results from the experimental study in terms of total stresses shows that sand at high pressures behaves similar to a normally consolidated clay.

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This paper deals with the measurement of copper contaminant migration in soils by means of a fibre-optic sensor operating with yellow light buried in the soil. The resulting breakthrough curve is compared with a numerical analysis using the advection-dispersion equation. In order to examine the copper adsorption properties, a batch experiment was carried out. It was found that the copper adsorption on silica sand follows a Langmuir model at high concentration. The copper dispersion coefficient was estimated from the plume shape, assuming that a Gaussian distribution of concentration is applicable to the copper plumes. It is demonstrated that the measured breakthrough curve is in reasonable agreement with the one calculated from the dispersion coefficient or the longitudinal dispersivity and retardation factor measured by the batch method. The retardation factor is observed to decrease sharply with increasing concentration of copper solution up to 10 (g/L).

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A series of elasto-viscoplastic finite element analyses is performed to describe the long-term settlement measured at the reclaimed islands in Osaka Port. The compression modeling for the quasi-overconsolidated Pleistocene clays proposed by the authors has been incorporated to the procedure in which an elasto-viscoplastic deformation is assumed to occur even in the quasi-overconsolidated region (P₀≤P≤P_c). One-dimensional analysis is adopted for assessing the settlement of Sakishima and Yumeshima Reclaimed islands, whereas the plane-strain finite element analysis is carried out for investigating the deformation of the Pleistocene deposit beneath the sheet-pile composite revetment at Maishima Reclaimed Island. The proposed procedure is found to provide larger settlement for all cases compared to the conventional approach because of the consideration of viscoplastic deformation in the quasi-overconsolidated region. As for the case of the sheet-pile composite revetment, the effect of stress concentration due to ground improvement with SCP for the Holocene clay layer is remarkable on the underlying Pleistocene deposit. The measured settlement of the individual Pleistocene clay layers as well as the total settlement of the Pleistocene deposits are precisely described by the proposed procedure, whereas the conventional approach in which the instantaneous elastic deformation is assumed to occur in the quasi-overconsolidated region exhibits serious underestimation. From these results, the predictive accuracy of the proposed procedure is verified for assessing the long-term settlement at the reclaimed islands in Osaka Port.

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Changes in soil structure and overconsolidation in highly structured natural deposited clay as a result of sampling and setting in laboratory tests, together with their effects on the subsequent mechanical behavior, are numerically simulated in terms of unconventional elasto-plastic mechanics. To describe the mechanical behavior, a Super/subloading Yield Surface Cam-clay model is employed. This model allows a description of the decay of soil structure, loss/increase of overconsolidation and evolution of anisotropy with ongoing plastic deformation from the process of the soil sampling through the unloading with swelling up to the subsequent tests. The sampled clay subjected to isotropic unloading and/or one-dimensional unloading with swelling down to the first stage of vertical loading level, displays a response to some degree, different from that of the soil at the original sampling site ; for example, an overconsolidated sample subjected to isotropic unloading with swelling will display rewinding behavior in a subsequent undrained triaxial compression test, and “secondary consolidation”/“delayed compression” in a one-dimensional consolidation test. However, one-dimensional unloading with swelling, which is followed by one-dimensional compression test, will give better prediction of the in-situ “consolidation yield stress” than isotropic unloading. Artificially disturbed clay subjected to repeated undrained shearing after sampling suffers a significant loss of structure. This results in a drop in peak strength under subsequent monotonic undrained shearing tests, and in the compression index in one-dimensional compression tests, as described by Schmertmann.

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In this paper, an elasto-viscoplastic constitutive model with strain softening is developed for soft sedimentary rock using a newly proposed evolution equation for subloading yield surface originally invented by Hashiguchi (1980). In the model, associated flow rule is adopted and tij concept, which can take into consideration the influence of intermediate stress on deformation and strength of geomaterials, is used. In the model, as is the same as Cam-clay model, plastic volumetric strain is used as hardening parameter, which is widely accepted by the researchers who specialize in the constitutive model for geomaterials. The application of the model to the experimental results of soft sedimentary rock indicates that the model not only can describe the time dependency, such as strain rate dependency and creep, but also the strain softening behavior of geologic materials. The material parameters involved in the model have clear physical meanings and can be easily determined with triaxial compression tests and creep tests.

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The possible existence of a vast amount of methane hydrate around islands has attracted attention as the largest potential hydrocarbon resource in Japan. At the same time, several production methods have been considered to extract the gas from the hydrate zone. Although it is known that the hydrates pose significant obstacles to drilling and production operations, there is at present only limited knowledge on the mechanical behavior of hydrate-rich zones, which is necessary to understand the stability around the site. In order to know the properties of methane hydrate and/or its sand mixtures, a series of tests was carried out on artificial methane hydrate-sand mixtures, using low temperature and a newly developed high confining pressure triaxial compression technique. The sediments used in the mixture were obtained from a 207.75m sea bottom core from the Nankai Trough, located 1152.75m below sea level. The specimens used were prepared by compressing a mixture of artificial methane hydrate and the sediments with a volume ratio of sediments to the whole of specimen. On the basis of these experimental results, the factors affecting mechanical properties of the hydrate and sediment mixtures are discussed. It is very essential to collect more data on the properties of methane hydrate and/or sedimentation (soil) mixture to understand the stability of any attempt at methane hydrate production.

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Several chemical reactions controlling the alkalinity of solidified/stabilized sludge using a low alkalinity additive (mainly composed of gypsum and slag) are investigated experimentally. The influence of curing conditions (open air or sealed) on the alkali leaching characteristics of the treated sludge was evaluated from the viewpoint of carbonate uptake and leaching properties of cations (Ca, K, Na, Mg, Al and Si). Modified batch leaching tests were conducted for the treated sludge cured in both open air and sealed conditions to characterize the alkali and cation leaching behaviour. Mineralogical characterization was performed through X-ray diffraction (XRD) analysis, and the Calcimeter test traced the variation of carbonate amount in the treated sludge under curing. In addition, the type of hydration products in treated sludge was also estimated by the acid neutralization capacity (ANC) tests. Experimental results showed that open air curing has an effect to decrease the pH of solutions from batch leaching tests compared to sealed curing, since the sludge cured in open air contained more carbonate and less hydroxide than those cured in sealed condition. Promoting the carbonation of Ca(OH)_₂ by contact with carbon dioxide could reduce the alkalinity of treated sludge. In addition, the amount of magnesium carbonates (e.g. MgCO_₃) and the fraction of Mg ions in treated sludge could affect the pH of leached water.

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The objective of this paper is to evaluate particle crushing in the soil using the results of X-ray CT scanning without any destruction and sampling. First of all, the properties of X-ray CT data are discussed using its statistical consideration. Then, a method for evaluating particle crushing is proposed. This method is implemented by scanning simple granular materials using aluminum rods and soil. Then, a series of model pile loading tests are conducted for the materials of non-crushable and crushable soils. Based on the results of CT scanning for the model grounds, the effectiveness of the proposed method for evaluating particle crushing using X-ray CT data is confirmed. Finally, one of the effective usages of X-ray CT data in geotechnical engineering is convinced.

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All available solutions for the problem of bearing capacity on clays of anisotropic and nonhomogeneous strength are based on the assumption of either circular or Prandtl-type failure mechanisms. Although these solutions are rigorous within the concept of limit analysis or limit equilibrium methods, the formulations are too mathematical and exceedingly cumbersome and the bearing capacity value can only be determined through numerical optimization for each given combination of soil and failure mechanism parameters. By means of the upper bound approach of limit analysis, and adopting translational failure mechanisms, this paper presents analytical solutions for the bearing capacity of surface strip footings on clays of strength anisotropic and linearly increasing with depth. Closed-form expressions for bearing capacity factors in the case of smooth and rough footings, have been derived by considering two newly introduced kinematically admissible translational failure mechanisms with varying wedge angles. It was remarkable to find that the two mechanisms would render closed-form expressions for the bearing capacity factor if and only if the deformed region underneath the footing is set to be bounded by two vertical discontinuity surfaces. The derived formulas are expressed in terms of degree of strength anisotropy and a nondimensional parameter that reflects strength nonhomogeneity. Besides being the only closed-form solutions yet available for the bearing capacity of strip footings on clays with anisotropic and nonhomogeneous strength, the derived expressions have been found to not only provide upper bound values for the bearing capacity factor that compared favorably with available solutions, but also yield the best upper bound values when strength increase with depth becomes predominant.

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The effects of strain rates on the strain localization characteristics of soft rocks in plane strain compression tests were studied. Using digital image correlation method based on image analysis technique, digital photographs of the specimen taken by CCD camera mounted in a microscope at different stages of loading were analyzed and displacement and strain fields were obtained. The accuracy of displacement and strain measurements are found to be 2.625 μm and 0.0525% (for 5 mm × 5 mm grid), respectively. By analyzing the strain fields, important information regarding strain localization characteristics at three different strain rates were obtained. The results of the study indicate that strain rate has significant influence on the localization modes. Strain localization was observed before the peak stress. The switching of localization mode from highly concentrated strain accumulation mode for higher strain rate to diffuse and complex strain accumulation mode for lower strain rate were observed. The evolutions of strain fields during creep tests at different loads were also studied.

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Naturally deposited clays exhibit complicated mechanical behavior that differs from that of remolded clays. For example, clay in a normally consolidated state commonly exhibits softening in undrained shear tests or “rewinding” in a heavily overconsolidated state. The Super/subloading Yield Surface Cam-clay model (Asaoka et al., 1998, 2000, 2002) was proposed in an attempt to clarify the complicated mechanical behavior in naturally deposited clays. In this constitutive model, the concepts of “structure,” overconsolidation, anisotropy, and their evolution laws, are introduced into the modified Cam-clay model. In the present study, undrained triaxial compression tests and oedometer tests were carried out on two types of naturally deposited undisturbed clay, Pleistocene clay and Holocene clay, and the behavior was then simulated using the Super/subloading Yield Surface Cam-clay model. The findings of the present study are as follows:
1) For the two types of undisturbed clay, the Super/subloading Yield Surface Cam-clay model can simulate undrained triaxial compression behavior ranging from the normally consolidated state to the overconsolidated state, corresponding to various isotropic pressures using a single set of material constants.
2) In addition, the model can simulate one-dimensional compression behavior using the same material constants as those used for the simulation of the undrained triaxial compression behavior.
3) Through the simulation, the mechanical behavior of Pleistocene clay and Holocene clay, which have different loading histories and have undergone different aging effects, can be described by the different evolution parameters, as well as the elasto-plastic parameters.

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The sedimentary environment and the effects of sample disturbance on strength and consolidation properties of Busan New Port clays are examined through microfossils and radiocarbon age analyses and unconfined compression, K₀-consolidated undrained triaxial compression and extension tests and consolidation tests. In this study, only one or two samples, 74 mm in diameter and 100 mm in height, obtained from different depths, are used for the whole series of tests to provide small-sized specimens. The sedimentation rates of Busan New Port clays were (3.7-7.8) mm/year and higher than those for the coastal areas of the USA, Thailand and Japan. The in-situ undrained shear strength and consolidation parameters were estimated using Shogaki's method and compared with those of other test results and evaluated. Busan New Port clays are lightly overconsolidated clays. It can be seen that the consolidation settlements, which were greater than those estimated, were observed in Holocene Busan clay, are caused by the underestimation of the compression index and coefficient of consolidation values caused by sample disturbance.

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