Core samplings were conducted in offshore Sakhalin Island, Sea of Okhotsk, and in Lake Baikal, Russia, where shallow gas hydrates existed. To examine the mechanical properties of sea and lake bottom sediments, the handy vane shear and cone penetration tests were performed for the core samples on board. To evaluate the sample disturbance due to the exsolution of dissolved gas during sampling, the relations between the concentration of dissolved gas in the pore water and the strength were also examined. Moreover, laboratory tests which simulate the stress relief from bringing the samples to the sea or lake surface were also performed. Test results showed that the strength of soils become lower with the increase in degree of gas saturation on both on-board and laboratory tests. It was also showed that the in-situ strength can be estimated roughly from the disturbed sample.

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It has been discussed recently what is the effective way to dispose of the waste plasterboard produced at the construction sites. The disposal method of construction generated soil is another issue to be discussed. In this study, as it was assumed that bassanite produced from waste plasterboard and construction generated soil could be effectively utilized through liquefied stabilization method, the flow properties with a flow test and the mechanical properties in unconfined and triaxial compression tests were examined in the liquefied stabilized soil made from Kanto loam, slag cement B-class, bassanite, and water. Furthermore, the leaching properties of hexavalent chromium, fluorine, and boron were examined, as it was assumed that application of liquefied stabilized soil into geo-environment could be utilized. The test results showed that the consistency properties were kept enough fluidity for an hour after mixture of the above mentioned materials and that the mechanical properties had unconfined compression strength by more than 200kN/m² in a certain condition of material mixture. In terms of the environment aspect, it proved that the leachated amount of hexavalent chromium, fluorine, and boron was complied with the environmental quality standards for soil pollution.

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A simple model of e-log p relationship of natural clay deposits with highly developed structures due to cementation, effects is proposed. The model is based on a unique compression curve in normally consolidated region and parameters describing the degree and the effect of initial structure. The model was adapted to one-dimentional compression curves of 10 natural marine deposits, and the model fitted the experiment data fairly well. The level of the structure of marine deposits was classified into 4 groups, level 0 to level 3 depending on the largeness of structure parameter obtained by the fitting. The Holocene marine clays in Japan were in the level 1 and 2 close to 1, while the Osaka Bay Pleistocene clay is in the level 2 close to 3, showing that the effect of the structure is more significant.

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In this paper, a simulation for real-scale slope excavation experiment was reproduced using the SPH (Smoothed Particle Hydrodynamics) method. The method can treat large deformation problems because the method is based on the free mesh system. In addition, the constitutive models of geomaterials can be used directly. At first, slope stability analysis was carried out to validate the SPH method. The numerical results were compared with results of the safety factors provided by the Fellenius method. Then, a simulation for real-scale slope excavation experiment was carried out. All deformation processes, from the start of excavation to subsequent failure, were reproduced in the simulation. The numerical results obtained from the SPH method and the experimental results were compared. The SPH method was applied to excavation analysis, and the results demonstrated its applicability to the entire deformation process from the initial state to subsequent large deformations.

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We investigated the geomorphic transition and the existence of the reclaimed land by using the topographic map published in 1965 and 2002, and also chronologically comparing aerial photographs of the volcanic ash plateau in Kitami City, which is a major urban city in the Okhotsk region, East Hokkaido. Moreover, we also made a comparison between the ground conditions of the reclaimed land and the natural ground, based on the geotechnical information database created uniquely.
In the plateau examined, rapidly developed land, which was reclaimed from the 1970s, is included, and it became clear that such reclaimed areas are very vulnerable, judging from the N-values and the groundwater levels. It is presumable that such places are can be found in city areas all over the country, especially the newly developed residential areas. To prevent geotechnical disaster damage in each urban area, it is required to clarify how the landform was created and transformed afterwards. Thus, we must work out a master plan for disaster damage prevention, which can take care of not only the damages of underground lifeline networks, such as waterworks, sewers and gas pipes caused by the earthquakes but also daily failures caused by the vulnerability of the ground conditions.

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