In the following paper, we have taken constant strain rate drained triaxial tests and drained creep tests for porous tuff; Tomuro rock-one of Oya rock. Applying Vaid's concept on equation of state in stress-strain-strain rate to drained condition, and, moreover, by using Akai's concept on the essential relationship in stress-strain-time for saturated clay, essentially we try to explain time dependent behavior of soft rock that shows strain-softening.

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For a numerical method for the excavation problem in rock mass to be adopted in the design and construction of, for example, a large-scale cavern, its input data must be determined from geological survey and in-situ test objectively. The present paper proposes a method to determine the input parameters for the MBC model from measured convergences during tunnel excavation. The tunnel excavation preceding, for example, a large-scale cavern excavation is regarded as an in-situ stress relaxation test. The proposed method is applied to the measurement data at the Kazunogawa power station constrcuted by the Tokyo Electric Power Co. Inc. It is shown that the estimated dip angle agrees with the reported value.

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A series of cyclic triaxial tests was conducted to investigate liquefaction and post-liquefaction recompression characteristics of sands containing non-plastic silts as the fine which were prepared by tamping and water sedimentation at laboratory. In particular, the investigation was focused on the effects of relative density, silt content and kind of silt on those characteristics. Based on the results from tests, the emphasis was placed on the following: (1) There is a unique relationship between normalized strength ratio and number of load cycles, which is independent of the above three influential factors. (2) Post-liquefaction volumetric strain can be correlated to the liquefaction safety factor defined by the cyclic strength ratio, irrespective of the fine content.

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Soft clays treated by the lime columns undergo high-temperature consolidation for long period. However, the influence of high temperature on soft clay is not well studied yet.
In the present study, experimental study on the heated-drain consolidation is conducted by model equipment in the laboratory. Results of the experimental study are analysed by (1) radial-zoning of soft clay for heated-drain consolidation, and (2) coupled hydro-thermo-mechanical analysis. After the study, heated drain is found to accelerate the consolidation and create stronger structure of clays. In addition, clays near the drain are found to undergo secondary consolidation.

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To characterize a reservoir created by hydraulic fracturing, an application of fractal dimension analysis to source distribution of AE (acoustic emission) is examined. Applicability and reliability of the fractal dimension are studied by using distributions of points modeling AE sources. Based on the results, fractal dimensions are obtained for AE source distribution induced by hydraulic fracturing in a 1000m deep well. Comparisons between fractal dimensions obtained and geological surveys elucidate that the fractal dimensions is promising to characterize the reservoir from the source distribution of AE.

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The authers are conducting a series of research studies on the effect of earth pressure on closely bored tunnels. At the first stage centrifuge tests were carried out with a pair of tunnelling models. In these experiments the characteristics of the earth pressure in sandy soil were investigated when the ground surrounding tunnels had been yielded by tunnel boring work. At the same time simulation analysis by DEM model was carried out and the mechanism of increasing bending moment of first tunnel by occurance of tail void of second tunnel is clarified.

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The direct shear test is one of the most suitable methods to determine the strength and deformation characteristics of marine clay. To increase the popularity of the direct shear test method, this paper presents the relation between the shear strength and deformation characteristics of marine clay obtained from direct shear test with other test such as: unconfined compression test, triaxial compression and extension tests, direct simple shear test, field vane test and cone penetration test using numerous test data.

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In this paper, we investigate distribution characteristics of granule strength for various granular soils according to the experimental results. The main conclusions are as follows. Namely, statistical distribution of granule strength can be approximated fairly well by negative binomial distribution. Also, granule strength is different by material and particle size. Particularly the smaller particle size becomes, the more average rupture stress increases. Furthermore, the drop of granule strength by submersion is clearly recognized, etc.

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In Sand Compaction Pile method, when the vibroflot is inserted into a saturated clay layer, the clays around the sand pile are disturbed and even outside the improved area the excess pore water pressure is generated and the shear strength of clay decreases. In this paper, based on the laboratory test results including the multi-directional simple shear tests for undisturbed samples, the effects of the disturbance by the SCP driving operations on the shear strength of clay outside the improved area and the border of the region affected by the SCP driving are investigated. In conclusion, it is clarified that the shear strength of clay decreases immediately after the SCP driving and the border of the disturbed region is given by the surface of sliding under the passive earth pressure condition.

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Generally, discontinuous rock masses show both strain-hardening and strain-softening behaviors. Therefore, in numerical studies of rock mass deformation, it is very important to construct a strain-softening constitutive model.
This paper presents an elasto-plastic constitutive model for a rock interface. The constitutive model is based on stress history tensor which derives both strain-hardening and strain-softening characteristics. The procedure to determine values of material parameters in the constitutive model is discussed based on the experimental result on mortar interface.
The applicability of the constitutive model is numerically studied by means of the finite element analysis. The comparison between the numerical and experimental results on interfaces is carried out. It is found that the constitutive model simulates both strain-hardening and strain-softening behaviors of interfaces.

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In the construction of embankment with high water content cohesive soil using non-woven geotextile as horizontal drainage, transmissivity of the geotextile has important function. The transmissivity decreases by various effects, especially, the effect of clogging by which geotextile catches soil particles can be serious. In this study, in order to investigate the above effect, we made 4 kinds of geotextile 5 different levels of clogging condition respectively, and carried out transmissivity test for the clogged 20 samples. As results, it was cleared that transmissivity of clogged geotextile decreased with increasing of confining stress exponentially in spite of clogging condition. Besides, it was cleared that geotextile whose density was looser performed higher transmissivity in no using condition, however transmissivity of the geotextile decreased easier with progressing of clogging.

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Over 250 caisson type quay walls were damaged in the Kobe Port during the 1995 Hyogoken-Nanbu Earthquake. The typical damage was observed, seaward horizontal displacements of the caisson walls were around 5m at maximum and 3m on the average and around 1m settled, the caisson walls also suffered tilting. To investigate the mechanism of damage, we carried out geotechnical investigations and field measurements including in situ freezing sampling and effective stress analysis. The results of effective stress analysis suggested that the decrease in shear resistance due to excess pore water pressure increase in the foundation soil under the caissons and in the backfill soil increased the deformation of the caisson walls.

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The stability of sheet pile supported excavations in saturated sandy ground is investigated numerically. The rigid plastic FEM incorporating the linear constraint conditions is used in the analysis. Two cases of sheet piles; fixed type and cantilever type are analyzed under both the undrained and drained (steady flow) conditions. Under the drained condition, the cantilever sheet pile case exhibits failure at a water head, half of that in fixed type. Under the undrained condition, the cantilever type sheet pile case exhibits failure at a water head of one fifth that in fixed type. Although the sheet pile is supported by struts, fully fixed sheet pile assumption should not be made in some cases of the stability analysis.

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Elastoplastic models for sand named t_ij-sand model and kinematic t_ij-sand model have been proposed which can describe properly the stress-strain behavior of sand under three dimensional stresses. These models can take into account the influence of intermediate principal stress on the deformation and strength of sand by using modified stress t_ij. However, they can not sufficiently describe the deformation and strength characteristics of sand by using unified soil parameters, when the change in confining pressure and void ratio are involved.
In the present study the previous models are extended to one which can describe not only the influence of the change of void ratio and confining pressure but also strain hardening and softening behavior by introducing a concept named “state variable” based on critical state of sand and Hashiguchi's sub-loading surface concept. The present model is confirmed to be valid by analyzing some triaxial compression and extension tests under drained and undrained conditions on Toyoura sand with different void ratios and different confining pressures. It is shown that the present model can predict well these influences.

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Overturning of mobile cranes frequently occur on construction sites. Investigation of these accidents confirmed that one cause of the accidents is penetration of the outriggers into the ground. From the above point of view, this paper examines the result of bearing capacity tests on model ground. Both strength and deformation characteristics for the partially saturated ground are investigated. Furthermore, a theoretical stability analysis is developed by both static and kinetic formulations. The results indicate that penetration of the outriggers into the ground (i. e. depth of penetration and its speed) greatly influence the stability of mobile cranes.

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Earth pressures on and deformations of buried flexible pipes, precisely measured in 22 centrifuge model tests, were compared with FE elastic analysis. In the analysis, effects of friction force acting on the test container and stress dependency of soil's deformation modules were considered. Analyzed results conformed well to the test results, clarifying the mechanism of change in the mechanical behavior of the buried flexible pipes due to the following factors: pipe flexibility, type of pipe installation, and ground material. The analyzed results showed that the behavior of the pipes during the sheet-pile extraction was governed by the appearance of both vacant holes at the zones where the extracted sheet-piles initially occupied and loosened zones near the vacant holes.

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The authors investigate into the mechanism of the occurrence of the liquefaction-induced ground displacement based on case studies during past earthquakes, tests on the characteristics of liquefied soil and on experiments by model grounds, and present fundamental knowledge in order to estimate the magnitude of the horizontal ground displacements. They propose a semi-empirical and semi-theoretical formula for estimation of horizontal displacements of sloped ground, where gradient of ground surface, thickness and N-values of the liquefied soil are taken into consideration as influential factors to the magnitude of the ground displacements.

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This paper discusses the reduction and subsequent recovery and increase of shear strength of clay in the vicinity of soil-cement column. Laboratory and field tests were conducted to investigate the effects on surrounding clay during and after column installation in soft Ariake clay. Discussions were made on the mechanism of strength change of the surrounding clay by considering the thixotropic recovery, reconsolidation effect, penetration of cement slurry and diffusion of exchangeable rations after construction. On the basis of field observation, it is recommended that the increase of shear strength of clay can be taken into consideration in the bearing capacity and stability analysis of the composite ground.

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The cross-hole test is useful for evaluating the channel system developing in a fractured rock mass. The pressure responses observed in a series of cross-hole test that is carried out at a dam site were analyzed. The rock of the site was mainly composed of the mixture of weathered granite and gneiss and had many fractures in it. Some channels of high permeability are existing in this weathered fractured rock mass. Also, some major fractures that are filled with fault clay have low permeability and act as the barrier interrupting groundwater flow. The patterns of the pressure response observed in the test were divided into 5 types. These types are closely related to the geometry of channels with high permeability and barriers existing in the rock mass. The effect of those channels and barriers on the pressure response are analyzed by using an idealized channel network model.

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In order to evaluate stability of reinforced retaining walls, it is required to know the relations between displacement of a wall, tensile force of reinforcements, earth pressure against the wall, frictional force on reinforcement and so on. In this study these relations were observed in the finite element analysis taking into account the strain level of the backfill soils. As the results of the analysis, it was made clear that tensile force of the reinforcements and earth pressures against the wall as the small strain level of backfill soil are relatively small compared with those which are estimated in the current design. When the failure of backfill soil occurs, the tensile force and the earth pressures coincide with those in the current design. The relation between earth pressure against the wall and tensile stress of the reinforcement according to the wall displacement were clarify from this research.

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In order to establish the limit state design method for pile foundations, it is necessary to develop the adequate analysis method that can fully express the ultimate behavior of pile foundations. Although several analysis methods for pile foundations have been proposed, mainly on the basis of small-scale model tests, the behavior of pile foundations is considered to be significantly influenced by the scale effect, the pile group effect, horizontal spacing of piles and so on. Authors executed the lateral loading test using the full-scaled 3-by-3 pile foundation with 1.2m of diameter, and traced its critical behavior up to the ultimate limit state. Based on the test results, the applicability of the nonlinear analysis model, considering both of soil reaction and M-φ properties of each pile, was precisely examined. And finally the design constants of nonlinear ground reaction characteristics were discussed including the past test results.

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The nondestructive test (SIT) using the impact wave was applied to the investigation of foundation piles in Hanshin Expressway damaged by Hyogoken-Nambu Earthquake. On application of the test, the authors developed an analytical technique for the measured wave data, to remove some effects of the multiple reflected waves caused by the footing or the damage at around the top of pile. By comparing the analytical results with the visual investigated data, it was confirmed that the developed analytical technique was well applicable to the damage investigation of piles. Moreover, the authors tried to apply SIT with the developed analytical technique to damage investigation of piles in reclaimed ground, followed by elucidating the correlation between the degree of damage of piles and the residual displacement of ground or foundation.

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Deformation in collapse has been studied with a triaxial test apparatus modified for unsaturated soil. Wetting tests, in which the condition of suction and stresses were known, were conducted under isotropic stress state for compacted clay specimens. Deformation, absorption and appricability of the ordinary constitutive model for unsaturated soils are discussed for the test results. It was found out that collapse, which occurred under isotoropic stress state, has similar tendency with that measured with oedmeter type test apparatus in past, and that shear deformation after collapse in different stress paths agrees with expectation by the ordinary constitutive model.

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In order to obtain better information of soil with stratification and contaminated zone of subsoil, two types of cones for measuring the resistivity of soil were developed. To examin the feasibility of the instrument the laboratory experiments were carried out using the cones and consolidation test apparatus. The results showed that the theoretical relationship between resistivity and voltage for soil can be applied in fields.

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Monte Carlo simulation was performed with respect to the uncertainty of soil parameters for harbour structures. Based on the concept of minimum total cost, including failure loss, the optimum safety factor was investigated for sheet pile and gravity quaywalls when circular arc slip method was used in the stability analyses.
The author showed an empirical relation to determine the optimum safety factor as given by: F_opt=0.85(1+log₁₀n)V. Here, n and V were used to describe the importance of structures and variance of soil parameters, which were discussed from the viewpoints of damage degree and the state of the art of soil survey and test techniques.

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In this study, to investigate the effect of basement for maintaining temperature, ground and room temperatures of some type models which were constructed of cement mortar were measured. From the results of the test, it was found that maintaining temperature of basement was affected by temperature of soil and basement was comfortable. And, to analyze temperature distribution of around basement, thermal properties of soil were investigated by experiment. From the results of the test, it was found that thermal properties of soil were affected by mainly water content. Then, effect of adiabatical materials for maintaining temperature of basement was confirmed by comparison of consumption of energy for maintaining the room temperature constantly.

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Dynamic behavior of an actual soil-pile-structure system during earthquake has been investigated using centrifuge model tests in order to check its stability against soil liquefaction and particularly the effect of liquefaction on the stiffness of group piles and its between soil. The model of this system, being composed of a 4x4 pile supported structure and a sand deposit, was precisely constructed in a larger laminar container. It was found that the pile foundation has no obvious efficiency in protecting the soil from liquefaction. The system, however, showed a sufficient capacity against soil liquefaction for a seismic input level of 175gal. This study also confirmed that dynamic centrifuge model test technology is a very powerful tool for evaluating seismic stability of actual soil-pile-structure systems.

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