The stability of slurry trenches constructed in sandy ground has been estimated by a few methods based on the limit equilibrium method. They are, however, insufficiently considered on an assumed shape of failure plane and lateral confining forces acting on a sliding soil mass. The 3-D elasto-plastic FEM that combines a shear strength reduction method to estimate a global safety factor and the shape of failure surface was applied to the stability of the slurry trenches. The applicability of this method was verified by comparing the results obtained from the centrifuge model tests on the slurry trenches with several lengths. In addition, the relationship between mesh size and precision of the safety factor was investigated for actual use.

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Shear modulus G of clayey soil at small strain level is discussed in this paper. The authors developed a new direct shear apparatus which is equipped with loadcells inside wall of the shear box and a pair of bender elements (BE) at the top and bottom plates so that mean effective stress σ_m′ and shear modulus G can be evaluated during consolidation and shear processes of consolidated constant volume direct shear test. Based on the test results, the relationships among void ratio e, mean effective consolidation stress σ_m′ and shear modules G are compared with the relationships among e, σ_m′ and Young's modulus E measured by cyclic triaxial loading. A simple equation is proposed based on the observed relationships and it is also shown that the change of G during and after drained creep is due to the combined effects of development ar deterioration of soil structure and change of void ratio. Strong dependency of shear modules G measured by BE during constant volume direct shear test on the effective mean stress σ_m′ is also found and the relationship between shear strength and shear modules G is discussed.

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A method for seismic stability analysis is proposed. It was developed based on the modified Fellenius method, applying the horizontal seismic force the cyclic shear strength of clays with initial drained shear stress as the resistance force on the sliding plane. Not only safety factor but also deformation and pore pressure developed in the vicinity of sliding plane can be evaluated in the present procedure. In order to verity the proposed method a case history in which fills developed on the clay grounds were collapsed by seismic loads were simulated. It was confirmed that the safety factor and the settlement obtained by the proposed method are in good correspondence with those of practical cases.

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This is one of the studies aimed at quantitative evaluation of the indices for rock mass classification that deals with “judgment method by the hammer tapping”. In this study, we examined the tapping test and unconfined compression strength using boring core of granodiorite, which was gathered at Kijyo in Miyazaki for application of practical problems. As a result, we showed “response sound pressure pulse inclination” can be applied as a quantitative index, like N-value of soil boring log, for strength and ductility of stratum. So we propose this inclination to be used as a quantitative index for rock mass boring core.

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We explored the effects of water saturation and strain rate on the tensile strength of rock. Radial compression tests and tests exploiting Hopkinson's effect were performed for various strain rates on three different types of rock, samples of which were either saturated with water or dry. There was an increase in the tensile strength of rock not only in the dry state, but also with an increase in the strain rate in the saturated state. It was also especially recognizable that the dynamic tensile strength of rock in the dry state was proportional to approximately a one-third multiple of the strain rate no matter what the type of rock. In addition, water saturation decreased the tensile strength in the dry state of Kimachi sandstone and Tage tuff, both with high porosity, but no significant difference could be recognized between the dry and the saturated states of Inada granite, which has a low porosity of 0.49%.

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In order to understand the shear and hydraulic properties of the joint of bentonite buffer for geological disposal of high level radioactive waste, single plane shear tests and permeability tests were conducted. Two types of bentonite specimens, compressed in the laboratory and compacted at the test site in Kamaishi Mine, were prepared considering construction methods. From these tests, the joint part of the bentonite buffer is the weakest and the most permeable part. However, its influence on shear strength and permeability decreases, after the bentonite buffer is saturated and the effect of swelling is appeared.

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The unconfined compression strength has been an important index for the design of air cement treated ground. In this paper, undrained shear behaviors of air cement treated soils were cleared out for the soil with different void ratios nd degree of saturation in a consolidation pressure range of actually assumed in a field. It was proved that the shear strength depended on the void ratio and the confining pressure affected the volumetric strain and excess pore pressure behaviors. The unconfined compression properties were useful indices to assume the strength for the soils with different void ratio. However, the values by the unconfined compression test were larger than that by the triaxial compression test, that needs some care in the design.

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There have been very few experimental results on mechanical properties of natural volcanic breccia. A series of triaxial compression tests under undrained condition were performed to elucidate the effects of the percentage of clasts, specimen size and maximum clast size on its strength and deformation behavior. The results suggest that the effect of the percentage of clasts is small, even though the internal friction angle become large and the deformation become inhomogeneous when the percentage of clasts exceed 20%. As to the effect of the specimen size, the mechanical properties are not largely different between specimens of various diameters up to 30cm although the internal friction angle is slightly small for large specimens. Moreover no effect of the maximum clast size is recognized on mechanical properties.

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Large part of deformation and failure of rock masses are governed by both characteristics of geometrical distribution of discontinuities and those of mechanical behavior in a single discontinuity. It is thought that stability of rock structures extremely depend on not only existent discontinuities but also new cracks which are generated and progress due to loading or excavation. In this paper, a new approach is proposed for modeling generation and progress of cracks due to shear and tension failure in the matrix by using distinct element method. Next, applicability of the approach are verified by means of comparison with experimental results by using base friction modeling apparatus. As applications to field problems for discontinuous rock masses, simulation of underground opening excavation is carried out.

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For coarse material fill standardized laboratory shear tests are unsuitable for the determination of shear strength due to the particle size problem. This paper presents an extrapolation method for shear strength of a coarse material fill from laboratory shear tests performed on smaller grain samples. Experimental work consisted of three series of box shear tests, and triaxial compression tests on samples of various grain sizes with the same degree of density (Dc) at the site. Shear strength at the site was evaluated by applying the “extrapolation method”, and compared with data obtained from field direct shear tests. It shows that strength evaluated based on the laboratory tests show almost equivalent strength, or a little less strength than observed field strength. The result from this study proved that shear strength of a coarse material fill could be estimated from a series of standardized laboratory shear tests.

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In order to clarify bearing capacity of a structure-sand ground system subjected to various types of loading, a series of model tests were carried out under several static and cyclic loading conditions. It was found that; (1) lateral flow behavior of the ground depends strongly on the settlement performance of a structure, (2) bearing capacity of the ground can be evaluated by a failure envelope which is depicted in M-V-H plane irrespective of the difference in loading conditions, and (3) stability of the sand ground-structure system may be evalutated by using the parameter V_δ/V_ρ which is adopted as the measure of lateral deformation volume in this study.

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The dynamic behavior of the pile during STATNAMIC test can be modeled as the vibration of single degree of freedom system. In this paper, the spring characteristics are assumed as a perfect elasto-plastic bi-linear spring. Unknown parameters of nonlinear spring, initial stiffness and yield displacement, are identified by extended Kalman filter. Dynamic response analysis using the identified parameters was carried out to confirm the accuracy of identification. Time histories of displacement and velocity at the top of the pile show close agreement between the measured and calculated results. The static bearing capacity from the analysis is also close to the static load test results.

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Deformation behavior of drainage pipes under high fills was investigated through centrifuge model tests. In the tests, a dry sand was trapezoidally backfilled around small model pipes with different flexibilities; fills were constructed around the backfilled areas with different soils; lead shot was placed on the model ground to create overburden pressures equivalent to those due to prototype fills with heights up to 100m. Measured deflections and bending strains of the pipes fully quantified effects, on the deformation of drainage pipes, of pipe flexibility, installation method, cover height, fill material, and thickness of fill under the pipe, and they did not conform to those calculated in accordance with a current design standard, indicating the necessity of a new rational design method.

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Based on the construction records and the previous researches, the excavated area, the tail clearance, the dynamic equilibrium condition, the rotation direction of cutter face, the slide of shield, and the ground loosening at crown of shield are considered to give the influence on shield behavior during excavation. In this paper, the theoretical dybamic load model on shield was proposed, taking account of the above-mentioned conditions. The simulation and the sensitive analysis on shield behavior were carried out. The obtained results were examined, based on the theory and the empirical law. As a result, it was confirmed that the proposed model can represent the shield behavior reasonably.

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Laboratory oedometer tests were conducted to investigate the effects of heating on promotion of secondary compression of peat. From the test results, it was confirmed that the rate of settlement of peat in the range of secondary compression was increased drastically by heating. Effect of heating on settlement promotion is incredibly larger for peat than for clay. After cooling the specimen, resettlement followed by small rebound was observed. The rate of resettlement, however, was so small that the long term compression tendency of peat could be reduced upon cooling

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Single particle crushing tests have been carried out on a number of different component minerals in order to investigate the influence of particle shape, size and mineralogy on the nature of the particle crashing. Several patterns of particle crushing were identified from the data. These were shown to be related to particle shape and mineralogy. A close correlation was found between particle crushing strength and corresponding shape and size.

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A series of test simulating the process from sampling to unconfined and UU triaxial compression tests for overconsolidated highly organic soil are performed. The influence of residual effective stress change on unconfined compressive and UU triaxial strength are examined, and a method for predicting in-situ strength from the relationship between residual effective stress and unconfined compressive srength is proposed. From the test results, it is found that strengths obtained from unconfined compression test with suction measurement can be reasonably corrected to estimate in-situ undrained strength by applying proposed method.

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A simplified procedure for evaluating the liquefaction-induced flow in the slightly inclined slope is examined. The flow failure in the slope where the ground surface and the basement are slightly inclined at the same gradient is modeled as a one-dimensional problem. Using the conventional two-dimensional liquefaction code based on the effective stress, we proposed a new procedure. This procedure can simply calculate the liquefaction-induced flow. In this procedure, the existence of the initial shear stress by the inclination of the basement is considered to be an influential factor of the ground flow. By comparing the proposed procedure with Orense's analyses and with the case studies during past earthquakes, the applicability of this procedure is evaluated.

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