Elasto-plastic constitutive models for the undrained strain softening behavior of normally consolidated clays and mud rocks are proposed by using the non associated flow rule. Parametric studies are performed on three proposed yield functions to examine the applicability and limitation of the models. The simulated strain softening behavior is compared with the undrained triaxial compression test results for alluvial clay and diatomaceous mud rock. It is concluded that one of the proposed models is appropriate for the simulation of undrained stress strain relations taking account of the strain softening behavior.

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Geological disposal of high-level radioactive waste (HLW) in Japan is based on a multibarrier system composed of engineered and natural barriers. In a repository for HLW, complex thermal, hydraulic and mechanical (THM) phenomena will take place, involving the interactive processes between radioactive decay heat from the vitrified waste, infiltration of ground water and stress generation due to the thermal loading and the swelling pressure of the buffer material. In order to evaluate the performance of the buffer material, the coupled THM behaviors within the compacted bentonite have been modeled. The coupled THM processes in the near field are simulated with fully coupled model. It is indicated from the investigation that re-saturation time of buffer is strongly dependent on the water pressure in the rock mass. However, it is not showed high dependency on the permeability of rock mass if the intrinsic permeability of rock mass is in the 10^-13-10-^-18m² range. Furthermore, it is found that the maximum temperature in the buffer predicted by the coupled analysis is lower than the uncoupled case.

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Based on constant-head permeability tests, seepage instability characteristics in sand and gravel with different particle properties are summarized as follows. The critical hydraulic gradient for seepage failure depends on various factors such as the relative density Dr, the uniformity coefficient Uc and the grain shape factor FU. Instability behavior is different in different soils such that a poorly graded soil (Uc<4) shows grobal boiling while well-graded gravelly sand (Uc>4) undertakes a segregation between gravel and sand. Among well-graded soils, some may exhibit a local piping failure at hydraulic gradient much lower than the theoretical gradient, which can be differentiated based on particle gradation curves.

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The objective of this study is to investigate experimentally the steady state excavation performances under constant cutting depth, especially the specific cutting energy, of a disc cutter bit in a free edge part of mortar specimen. Here, the tangential, lateral and normal forces acting on the disc cutter bit having three tip angles and the amount of debris were measurd for several cutting spaces and cutting depths. As a result, it was observed that the specific cutting energy, i. e. the ratio of the rotation work of the disc cutter bit and the amount of debris, increased with increment of cutting depth, took a minimum value at tip angle of π/4 rad and decreased with increment of cutting space.

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A series of undrained cyclic triaxial tests was carried out to investigate the effects of density and confining stress on liquefaction resistance of isotropically consolidated the coarse-grained reclaimed gravelly soil obtained from the reiquefied area on the man-made islands in Kobe (Port Island and Rokko Island). Test results shows the followings.
Reclaimed soil of Port Island is a granite-origin gravelly soil (locally called Masado-soil), that of Rokko Island is a mixed gravelly soil composed from mud stone-origin, tuff-origin and so on, and these reclaimed soils has a characteristics features of a high compressibility as the ground and the breakage of particle contacts. Although these coarse-grained soils contain a large portion of gravel, the liquefaction resistance is very low compared with that of the uniform and clean sand as Toyoura Sands and is depend on the density increased with the increasing confining stress.

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Knowledge on a relation between a crack pattern and stress state in a tunnel lining should help to evaluate soundness of tunnel linings by route surveying along a tunnel. Thus, the authors clarified in laboratory experiments that a tunnel lining having a cavity above the ceiling generates the same crack pattern of a shear crack along the ceiling and tensile cracks along the shoulders, even if a loading condition is different. The fact was confirmed by comparing stress conditions measured in real tunnel linings using two over-coring methods to the strain distribution in the laboratory experiments.

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In order to evaluate the drainage effect of gravel drains against liquefaction, a series of cyclic shear tests has been performed on a saturated sand under partially drained conditions by triaxial testing equipment installed a drainage valve. Firstly, the nature and strength characteristics of saturated sand under partially drained cyclic shear conditions were investigated. Then the cyclic strength under partially drained condition was formulated based on the testing results. A simplified method for designing gravel drains based on F_L method was developed by the formulated strength. As a trial design result of gravel drains coordinated the proposed method and the method based on seepage flow analysis, the propriety of the proposed method was recognized.

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In order to investigate the influence of preserving time and temperature on the variations of hydrogen-ion concentration exponent (pH) values of the acidified soil by air drying, site observation and laboratory test were performed. As a result, the hydrogen-ion concentration exponent (pH) values decreased with preserving time and the decreasing degree was influenced by preserving temperature. In addition, it was found that there was a straight relationship between pH and maturity which was calculated by preserving time and temperature, the engineering characteristics of the acidified soil by air diying could be estimated by simple evaluation equations used maturity.

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To investigate the seismic behavior and the eartquake resistant design methods of shield tunnel in transverse direction, a series of model shaking table tests and two kinds of analyses on the tests are carried out. The investigation concerns with the vibration characterisustics of tunnel and ground, the interaction effects between ground and tunnel, and the validity of analitical model of tunnel. In tests, the ground and tunnel materials were chosen according to the law of similarity, and the different structual characteristics of tunnel from the effests of transverse and circumferential joints were focused. In analyses, the seismic deformation method based on beam-spring model and the 2-D FEM dynamic analysis are adopted. As a result, it was verified that the former method could explain the results of the model shaking table tests better.

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In a three-dimensional analysis of slope stability in discontinuous rock, it is very important to identify discontinuities which should be evaluated. Also the seismic force and water pressure which act to the rock-blocks affect to their stability. In this paper, a simplified method for extraction of the unstable wedge is proposed by formulating the wedge type failure condition of the rock slope, considering the water pressure and seismic force. The failure condition is formulated without the shape and scale of rock-blocks. Therefore, the proposed method is useful to evaluate the stability of surface wedges in rock slope with complex form.

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The aim of this paper is to study the geotechnical properties of diatomaceous earth and its influence on a cut slope. In general, diatomaceous earth is extremely sensitive to small disturbance due to its much higher natural water content and compression index than those of other natural clays. The following conclusions are obtained from the present study: 1. The soil structure of diatomaceous earth can be easily destroyed by dry-wet cycle. 2. The liquid limit of diatomaceous earth is found to be lowered by disturbance. 3. Yielding properties of Takasu diatomaceous earth is less anisotropic than alluvial and Pleistocene clays. 4. Mechanical behavior of Takasu diatomaceous earth is similar to that of Osaka Pleistocene clays in terms of stress-strain-dilatancy characteristic. 5. Based on the experimental results, countermeasures against cut slope failure were suggested.

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As one of the system useful for planning underground repositories, such as radioactive waste disposal facilities, we develop a groundwater flow analysis system using the voxel analysis method. This paper shows an example of issues of mesh generation in the groundwater flow analysis using the conventional finite element method. Use of the voxel analysis method solves the issues and improves the analysis efficiency. The paper also discusses an influence of the voxel mesh with jaggy surface upon the accuracy of analysis results.

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The vertical seismic array records at the Kobe Port Island during the1995 Hyogoken-Nambu earthquake are simulated. One-dimensional ground models and a two-dimensional ground model are numerically analyzed by effective stress method. The 2-D model consists of the unimproved area including seismic array site and adjacent improved area by compaction method. The 1-D models represent those two areas respectively. Compared the 2-D model with the 1-D models, the improved ground affects the earthquake responses of the seismic array point. Moreover, the vertical settlement of the ground surface using the results of the 2-D analysis corresponds to the observational settlement.

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This paper presents the case study of a high embankment with the maximum height of about 90m consaucted by coarse-grained soil (weathered conglomerate rock with mudstone or sandstone) in river terrace district.
A series of compression settlement tests and triaxial compression tests were performed to investigate the settlement properties, stress-strain relation and strength characteristics on the embankment material. The field observation results of deformation and slope stability analysis of the embankment under construction was also described. The stability of high embankment slope was also evaluated from the relation between the observed deformation of embankment slope and the stress-strain curve of embankment material obtained by laboratory tests.

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Using the silty clay specimens that were compacted in the constant energy under various water contents, unconfined compression test, in which suction and volume change of specimen were measured, was carried out. The obtained stress-strain relations showed the tendency that depends on the initial degrees of saturation of the specimens. The measured relation between the suction stress and suction at failure showed similar tendency with the predicted ones based on the water content characteristic curve. This result means the possibility of estimating the suction vs. the adhesive force relation by unconfined compression test. And. when the suction stress was taken into account as a confining net stress, the stress state at failure followed the failure criterion for unsaturated soil proposed by Fredlund, Morgenstern & Widger. This result of silty clay means that the undrained strength follows the failure criterion based on the test results test under drained condition.

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The validity of laser scattering particle distribution analyzer for soil samples was examined by a relative index of refraction used in the analysis, soil suspension density for specimen in the experiment and the measurement range of particle size. The result was compared in the particle size distribution which was obtained by the laser method and JIS method and the reliability was examined. The results were as follows: It was confirmed that the laser method was easier to operate, quicker, more repeatable, and more reliable in comparison with the JIS method. The measurement of particle size distribution curve of the laser method showed smaller values for most soils than that of the JIS method. It was found that the laser method showed significantly more accurate results than those obtained by the JIS method. These results demonstrated that the laser scattering particle distribution analyzer was an appropriate method of determining particle size of fine-grained soil.

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The mechanical behaviour and material constants of in-situ compacted rock materials under high overburden pressure have been investigated based on the field measurements, laboratory tests, and computational analysis. By analyzing the actual settlements of rock zone during construction of several large-scaled fill dams and laboratory compression tests for rock materials, the elasto-plastic deformation of rock materials under high overburden pressures have been found to exist. Several factors affecting the compressibility of rock materials; mean grain size, grain size distribution, and void ratio have been investigated by detailed analysis of field measurements of several fill dams. As a result, a tentative procedure of estimating the material constants of in-situ rock zones based on the laboratory tests is suggested. Stress-deformation analysis of an actual rockfill dam during constructionand first res-oivor fillin g process by an elasto-plastic finite element method, using the constitutive equation by Sekiguchi and Ohta is canrried out. Good agreements between calculated and measured deformations and earth pressures are obtained.

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A series of unconfined as well as triaxial compression tests was carried out on specimens of Toyoura sand mixed with cement. The behaviour of elastic Young's modules at extremely small strains, together with its variation with strain and stress was examined over a wide strain range (10^-6-10^-2), and also over a wide stress range (0-2.4MPa). In this paper, methods for measuring properly stress-strain and strength characteristics of weakly bonded geomaterials such as cement-mixed sand are in detail discussed. Effects of cement content, curing period, effective confining pressure and its history on deformation characteristics of cement-mixed sand were each examined with attention paid to the interlink between elastic Young's modulus and strength. The results were interpreted against comparable behaviour of clean sand exhibiting no interparticle bondings.

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The foundation of the industrial water tank at Tachibana-wan Power Station is very large with a diameter of 85m. Since part of the baserock is exposed at the ground surface and sloped relatively steeply, the depth of the baserock varies greatly in a single foundation. As a result of this, in an event of an earthquake, there is a danger of two-dimensional vibrations when a combined footing of a spread foundation and a pile foundation is used. On the other hand there is a danger of large torsional vibrations due to the difference in the length of the piles when only a pile foundation is used. Placing emphasis on the torsional vibrations of a large tank foundation built on an inclined baserock, the torsional stability, the deformation characteristics and so on of the piles and concrete slabs in an event of an earthquake were confirmed and evaluated by two-dimensional and three-dimensional analysis, and the design method of a large tank foundation on an inclined baserock was proposed and the optimum foundation type was selected.

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Since the baserock under the industrial water tank at Tachibana-wan Power Station is sloped relatively steeply, as well as being very large with a diameter of 85m, the depth of the baserock varies greatly in a single foundation. Errors in the bearing capacity evaluation may be large if the conventional pile driving method is applied to special grounds such as this. For this reason, the normally used “dynamic load test” and “statnamic load test” were performed, a pile driving method with high precision was deveropped and the vertical bearing capacity was confirmed. Furthermore, considering that the coefficient of subgrade reaction is dependent on the rate of loading, static and dynamic load tests were performed with a dynamic jack, and the coefficients near the tank's natural period were calculated, and the horizontal coefficient of subgrade reaction in an event of an earthquake was evaluated.

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While vision metrology is in principle well-established technology, many ambiguous aspects exist, if it is applied to construction site measurement. This paper treats its further application to tunnel profile measurement to exemplify its usefulness and to make the problems clear. The technic with one CCD camera was applied to the three-dimensional deformation measurement of a tunnel of seven meters in diameter. 272 retro-reflective targets and nine scale bars placed on the wall and additionally on the floor of 15m in longitude were imaged by 66 exposures. The object coordinates of the targets are adjusted by the bundle method. The result was compared with 20 check points which were observed by a total station and adjusted by free network. The root means square of difference was 0.548mm.

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Deformation characteristics of decomposed granite soils during liquefaction process ware experimentally discussed from results of cyclic tri-axial test. As a result, the accumulated dissipation energy at occurrence of liquefaction depends on the void ratio and flow limit value of the sample of decomposed granite soil, and the approximate liquefaction resistance can be easily estimated from the values of the accumulated dissipation energy. Furthermore, the decrease process of shear modulus during liquefaction is closely related with flow limit value, and has a hyperbolic relation to the accumulated dissipation energy.

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Skin friction acting on cast-in-place concrete piles is studied, which go through clayey soil strata to bearing strata. In loading tests, clayey soils deform under undrained condition, on the other hand, under actual structures, when loads are sustained long enough for consolidation, the soil deforms under drained condition. Influence of the different drainage conditions on skin friction is studied by numerical experiments and it is found that influence is not negligible when piles are fairly long, which indicates it necessary to examine further whether it is correct to evaluate skin friction for pile design based only on pile loading test results

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