In this paper, the progressive liquefaction process of the loosely deposited sand bed under oscillating water pressure on its surface is investigated theoretically by using the vertically one-dimensional model, in which the elasto-plasticity of the sand bed skeleton is taken into account. The changes of pore water pressure, effective stress and liquefaction depth in the sand bed with time are simulated during the initial time period after the cyclic pressure loading. The experimental results verified that the proposed analytical model expressed fairly well the progressive liquefaction process of the sand bed.

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This paper discusses the geosynthetic-reinforcement effect. The reinforcing effect arises from the equilibrium of inner forces between extension forces working to the geosynthetics and stresses induced in the soil media. In this paper, a series of model tests and their numerical simulations are carried out to examine this geosynthetics-soils mechanical interaction. The compacted soils are wrapped by geosynthetics and sheared in the newly developed loading test apparatus with monitoring the deformation and stresses. It is revealed that, throughout this paper, the geosynthetic-reinforcement effect is mobilized by confining the ‘dilatancy characteristics’ of compacted soils. And also, a numerical simulation technique to rationally explain the observed facts obtained from model tests is proposed in this paper.

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An attempt was made to examine the mechanism of ground deformation due to tail void formation in shield tunneling in soft clay by using a series of centrifuge model tests, in which the reproduction of stress-strain characteristics and boundary conditions is possible. After confirming the repeatability and reliability of the model test data, the mechanism of ground deformation was deduced from the data of ground displacements, pore pressures and earth pressures on lining. It was shown that the ground deformation mechanism can be well explained by newly defined three phases

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A framework of the multiscale analysis method based on the mathematical homogenization theory is explored within the context of strength evaluation for fissured media. The two-scale variational formulation with appropriate functional setting plays a crucial role in our modeling for a general class of heterogeneous media. In particular, this modeling method for a fissured medium yields the microscopic variational inequality whereas the macroscopic problem is a standard equality. The formulation is utilized to propose the numerical strategy for evaluating its macroscopic strength and its feasibility is discussed by means of mathematical statements and through several numerical examples.

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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 tapping test using specimens from an artificial rock and analyzed the tapping sound. We visualized that distribution of the sound pressure changes with time on the sound field around a hammer immediately after the tapping. As a result, we confirmed that the initial tapping sound had two propagation routes to the microphone as opposed to what was conceptualized until now. One is through the steel ball and the air afterwards, the other is through the air only.

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In order to evaluate the stability of rock structures, in-situ shear test is often performed to investigate the mechanical properties of rock masses precisely. At one site, the result of in-situ shear test performed on rock mass constituted by many rock joints, whose dip amount was comparatively larger, showed ductile shear behavior that shear displacement at the peak shear stress was very large. In this research, a numerical simulation of in-situ shear test was conducted using the discontinuous analysis method, for the purpose of examining the mechanism of such ductile shear behavior and clarifying the reasonability of shear strength obtained from in-situ shear test. As the results, the simulation showed similar tendency with the results of in-situ shear test, and the progress of shear plane under testing block could be simulated by considering not only behavior of rock joints but also failure of intact rock. Furthermore, it was recognized that ductile shear behavior was due to the deformation of rock mass under the shear plane, accompanied with the movement of testing block during the increase of shear stress.

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Many model shaking tests to date have suggestedextremely high strain-rate dependency in the rigidity and strength of liquefied sand. The present stud conducted, firstly, torsion shear tests in which liquefied specimens were subjected to monotonic shear at a variety of strain rates. Different from model tests, the present test results did not indicate rate dependency. In the second stage, moreover, the limited magnitude of strain in the above-mentioned tests were overcome by developing a new testing instrument. Tests on specimen of Styrofoam grains, which had very small buoyant unit weight in water did not exhibit rate dependency either.

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In the design of Hot Dry Rock system, it is necessary to predict configuration of reservoir after stimulation and water flow in reservoir during circulation. In this paper, the sliding of natural joints originated by the action of water pressure is assumed for the governing mechanism of hydraulic fracturing, and analysis of stimulation at Hijiori in 1992 is conducted by using Micromechanics-based continuum (MBC) model. Then the relationship between joint opening and water pressure during circulation test is assumed, and analysis of circulation test is conducted. In this analysis, the results of stimulation analysis is used as initial condition. Finally, the prototype of designing method can be suggested.

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In the present paper, an accurate imaging technique for looking ahead of tunnel face by use of 3 components receivers is proposed.
The reconstruction procedures of geological structure are as follows.
1) To receive the reflected waves from the geological boundaries by use of 3 components receivers.
2) To detect the incident direction of reflected waves.
3) To perform imaging by use of equi-travel time planes using the weight according to incident direction in order to decrease the generation of false image.
The proposed technique was applied to the actual field data. Consequently, the imaging results showed a good agreement with the observation report after completion of tunnel.

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A series of unconfined and tri-axial compression tests were preformed to evaluate confirm strength characteristics and failure behavior of foamed cement lightweight soil with much air. The followings were obtained from the present study; 1) Unconfined strength was evaluated by two parameters, i. e., air content and water cement ratio; 2) Failure patterns were classified as following three based on the tri-axial compression tests; shear, compression, and shear and compression failures. Thus, strength should be evaluated in each failure pattern. The shear and compression strength were evaluated, including the characteristics of strength decrease with the increase of effective confining stress.

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In engineering, to prevent damage of boulders due to their rolling down from slope, it is necessary to know that the rock is part of rock masses or a boulder and how deep it penetrates into the ground. According to authors' experiments, some interesting facts are found. The high frequency waves propagate with a very good directivity and the corresponding surface wave sharply decays. Based on above facts, a new portable nondestructive test system is made. Just using a steel hammer to hit the rock surface, the size of boulder in sensor's direction can be directly calculated in situ from reflection wave. Aim of this article is to present some results of indoor experiments and field tests obtained by this new system.

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A study on lateral resistance of pile foundation becomes an important issue in seismic design. In order to obtain effect of relative density D_r pile diameter D and flexural rigidity EI on lateral resistance behaviour of single pile in sandy ground, a series of model single pile loading tests in geotechnical centrifuge was carried out. In the model test, relative density D_r, centrifuge acceleration ratio n and model pile diameter D were selected as test parameters. Before the centrifuge model test, physical properties (M-ψ relations) of six model piles were investigated by bending tests of the model piles.

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Model tests using a small container were conducted to study the mechanism of deformation process due to liquefaction. In this paper, the condition of post liquefaction ground was examined from the view point of compressibility of soil after liquefaction and the dissipation of excess pore water pressure in the ground. It was found that the pore water pressure change can be approximated using the equation of one-dimensional consolidation when the change of volumetric compressibility is taken into account. Furthermore, the boiling phase which behaves like a liquid was considered as the suspended condition of soil particles. An estimation for the change of the boiling phase thickness with time is proposed using the sedimentation mechanism of soil particles.

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A computational approach for analyzing boundary value problem with granular materials is developed based on the two-scale homogenization method. While the microscopic problem leads to the variational inequality which reflects microscopic friction-contact responses, the homogenized structure reveals the nonlinear response stemming directly from the averaged microscopic behaviors. Although the macroscopic problem is analyzed by the continuum-based FEM, the microscopic one is remodelled by rigid grains with spring and friction devices. In addition to the investigation of the effects of grains' configurations in a unit cell, the applicability of this two-scale modeling is discussed via representative numerical examples. In particular, the bi-axial compression tests on a plane specimen is simulated to illustrate the feasibility of the proposed method.

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To understand the liquefaction phenomenon, we developed a new technique to visualize relative density of saturated sand by measuring resistivity. Measured resistivity can be transformed into relative density by using the unique relation between resistivity and porosity, and the image of the distribution of relative density caused by a change in time can be drawn from the measurement of multi-electrode in the depth direction. In this research, we measured resistivity during liquefaction in a cylindrical vessel with multi-electrode in the depth direction under some conditions and visualized the results. From the results, we confirmed the existence of the contraction plane of sand that is the boundary between solid zone and liquefaction zone, and indicated that the plane develops from the bottom part to the surface.

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For applying the Extended SMP criterion to elastoplastic models for cohesive-frictional materials, a transformed stress based on the criterion is proposed, which is determined by making the criterion become a cone having the axis as the space diagonal in the transformed principal stress space. Furthermore, an elastoplastic model for geomaterials is presented, which takes the following three characteristics of goematerials into consideration. The first is strength and deformation characteristics in 3D stress; the second is dilatancy characteristics; the third is confining-pressure dependency of strength and deformation. The model is capable of predicting the stress: strain relations of cohesive-frictional materials and granular materials in 3D stress and a wide range of the confining pressure.

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This paper deals with the relationship among geological age, physical properties and compressibility characteristics due to slaking of compacted mudstones. The samples of mudstone have been of picked up in a restricted area of “Green-tuff region”. Through some experiments and conventional tests, it can be found out that the geological age of mudstone is strongly correlated to its physical properties of slaking and grain breakage. Moreover, it is revealed that the geological age and the physical properties are associated with the compressibility characteristics which can be seen in process of alternative repetition of wet and dry states or submergence of compacted mudstone. These relationships could be explained by the post-depositional physical change of rocks.

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This paper introduces the effect of fine grained soil to undrained cyclic shear behavior studied on a series of monotonic and cyclic triaxial tests conducted on mechanically compounded and undisturbed samples, respectively. The samples were classified into three types of soil based on the cyclic shear behavior obtained from results of the triaxial tests. Relationships between cyclic strength characteristics, growth of strain and physical properties are discussed on the each type of soils. One of the types mainly consisted of sand has less strength against liquefaction than the others containing more fines. It is also found that the cyclic shear strength is strongly related to clay content and plasticity index.

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It is difficult to effectively grasp the mechanical behavior of rock joints, since it depends on certain factors, such as the confining conditions, the material strength, the material friction, and the joint surface roughness. In this paper, direct shear tests on rock joints are carried out and the mechanical behavior of the rock joints is discussed in consideration of the normal confining condition, the material strength, the material friction angle, and the joint surface roughness. Then, a model for shear behavior is proposed, and the shear behavior of rock joints is estimated using the model. In comparison to the simulation in the experimental results, this model can reasonably present the shear behavior of rock joints. Moreover, it is able to anticipate changes in joint roughness during the shear process.

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When a saturated clay is sampled in an undisturbed manner, an effective confining stress due to the negative pore pressure induced by stress release restricts the volume expansion. The vertical and horizontal stresses to which the clay was subjected in the ground are smaller and larger than this isotropically confining stress equivalent to the mean principal stress in the ground, respectively. Thus the clay sample expands vertically and shrinks horizontally under undrained conditions.
The consolidation test developed herein empleys a specimen with a smaller diameter than the inner diameter of the ring that expands to the inner diameter of the ring under undrained conditions when the in-situ overburden pressure is applied. In this paper, using three kinds of clay samples with different plasticities consolidated from slurry, applicability of this proposed test procedure was verified; results from the conventional consolidation test procedure are also discussed.

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Mud soil sedimented in a irrigation pond generally is high-water-content and very soft clayey soil. Recently, it is necessary to develop the method for utilization of such a soil, as there is little space to dispose of it as industrial waste.
In this paper, it represents the results of the field test carried out to confirm the applicability of cement-stabilized mud soil as the fill material to construct the counter-weight embankment or widening of embankment in the repair or the reinforcement of the irrigation dam. The effect of crushed diameter of initial stabilized mud soil on strength characteristics and permeability of the crushed and compacted stabilized mud soil was investigated specially in this test program.

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This paper discribes the reconnaissance surveys using a helicopter-born electromagnetic method (HEM) and their verification results, also refferring to the importance of a reconnaissance survey and the significance of a resistivity measurement for the geological engineering.
As a result of the verification, consisting of the comparison between HEM survey results and the past geological/boring survey results, it is recognized that HEM is expected to have the sufficient resolutions powers in both horizontal and vertical directions in order to grasp the outline of the regional geology and its engineering problems.

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This paper investigates the relation between swelling and decay of strength during the wet-state of the drying-wetting of diatomaceous mudstone. A dry specimen in a triaxial cell was returned to the wet state by the use of back pressure. Loss of strength was confirmed from the result of the compression test of a wet specimen, even though confining pressure was given to the specimen to prevent swelling. The degree of loss of strength obtained from these tests is approximately equal to that observed for a specimen in an inundated condition. It can be concluded that the loss of strength during the wet-state is not connected with swelling. but rather depends only on the highest degree of desiccation attained during the drying-wetting process.

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The authors deduced the ground deformation mechanism during shield construction in soft clay from a set of field measurement data and corresponding centrifuge tests. Applicability of the ground deformation mechanism deduced was confirmed by the data of the spatial distribution of vertical strains around the tunnel, obtained from five different shield construction sites, where these shields were driven through the same soft clay, called the lower Yurakucho layer.

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For the purpose of evaluating rock mass stability around an underground opening, this paper proposes new strain criteria of rock and rock masses making use of the Hoek & Brown failure criterion, which has been widely accepted and utilized all over the world. One of the authors previously proposed the critical/failure strain, which has been used in tunnels or cavern constructions as a standard indicator of rock mass stability. It still has problems, however, that the critical/failure strain of an intact rock may not simply apply to rock masses and to the region of a large confining pressure. The results of this research imply that the new strain criterion for an intact rock can be made applicable to the region of a large confining pressure and to rock masses only in unconfined stress states. It should be noted, however, that the new criterion for rock masses is significantly larger than that for an intact rock in triaxial stress states.

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