From the view point of foundation engineering a research program continued to investigate the mechanical behavior of Hiroshima decomposed granite, by performing oedmeter tests, drained and undrained triaxial tests on undisturbed samples. Further tests were performed on individual rock forming minerals, quarts, feldspar and clay to interpret the integrated behavior of undisturbed sample. Importance on crushing of feldspar was stressed and a few suggestions were presented towards modeling of weathered decomposed granite.

View full abstract

The authors conducted a large scale centrifugal shaking table test on the seismic behavior of cylindrical retaining wall under liquefaction. The test was performed under 50G field using the scaled model with outer diameter of 20m in prototype scale. It was found that response of retaining wall does not follow the response of adjacent ground during liquefaction. Seismic component of strains on retaining wall are affected by the generation and dissipation of excess pore water pressure.
Three dimensional dynamic effective FEM analysis were adopted as the simulation analysis of the test. It was found that the maximum strain occurs at the middle depth of the retaining wall.

View full abstract

A measurement of sound velocities is one of the useful methods for evaluating elastic moduli of anisotropic rocks. Shear wave velocities have been almost always used in the determination of the elastic constants of rock specimens. However, the identification of direct shear waves in rockmass should often be difficult, due to mode conversion at boundaries and shear wave splitting. The present study discusses how to evaluate elastic moduli of anisotropic rockmass without any observation of shear wave velocity. The simulation study showed that the elastic moduli were very difficult to be determined exclusively by using the sound velocites of quasi-dilatational waves in a practical condition that the velocities in every 15 degree interval in three orthogonal planes with an accuracy of better than 2%. When the gradients of the error-functions with respect to the calculated shear wave velocities were combined with the information of observed dilatational waves, all of the elastic moduli could be effectively determined.

View full abstract

The aim of the present paper is to construct a constitutive model of soft rocks that can precisely describe not only strain-hardening-softening behavior but also dilatancy characteristics. That is, the Adachi-Oka's elasto-plastic constitutive model is modified by introducing a new volumetric strain dependent plastic potential function and by improving the stain hardening law. The model is evaluated through a comparison of the calculated results and the experimental results of tests on tuffaceous rock (Tomuro-ishi).

View full abstract

In this paper, investigations were carried out about the problem of size reduction in mudstone based on the analytical result of a lot of soil test data from mainly the point of viewing the change of gradation, clarifying the characteristics of size reduction which are derived from a slaking phenomenon and a particle breakage phenomenon, and together with this, classifying the size reduction. Furthermore, modeling was tried to realize this size reduction mechanism.

View full abstract

The authors conducted an extensive open-cut survey on a grouted rock mass, which is a Triassic formation of sandstone inter-bedded shale. The salient results are:
1) From the traces of fractured obtained on both the horizontal and vertical sections of the excavation, three dimensional images for the distribution of original and grout injected fractures were obtained.
2) The directional distribution of the grout-injected fractures coincided with the one for all the fractures. Directional group sub-parallel to the geological bedding structures showed less tendency to be penetrated by grout than those of vertical or nearly vertical fractures.
3) The water/cement ratio of the grout dropped from 600% at mixing to about 80% after getting hardened inside the rock formation.

View full abstract

For the purpose of some help toward the estimation method, authors developted back analysis scheme using nonlinear programming in heat conduction analysis based on the finite element method.
This paper demonstrates that the adotability of the back analysis method on the estimation of thermal characteristics of freezing ground is studied, and that the possibility of the back analysis method in the feedback system of field measurement results to design and temparature control in construction site using the soil freezing method is discussed.

View full abstract

Very deep boring investigations were carried out at two sites in the suburbs of Tokyo metropolitan area to understand systematically mechanical properties of sedimentary ground at great depth around big cities in Japan. In this paper, we described mechanical properties of sedimentary ground at great depth based on a series of laboratory tests using undisturbed samples. Furthermore, some approximate equations were given by considering geological tectonic movement history so as to demonstrate the distributions with depth about consolidation and strength properties of sedimentary ground at great depth, and their applicability was studied.

View full abstract

The behavior of a tunnel lining is a typical ground-lining interaction problem which depends on the relative stiffnesses of the lining and the ground as well as the initial stress conditions. In this paper a strict solution of the relative stiffness is derived for both full-slip and no-slip conditions at the ground-lining interface; moreover, the solution is modified for the interaction to be not affected directly by the ground movements due to the initial stresses before tunneling. The analytical results of different linings are quantitatively evaluated by using a common index, “support-stiffnesses”, for the tunnel lining, the surrounding rock mass and the total, which must be useful for practical implications and the further development of tunnel support design.

View full abstract

The distinct element method seems to have an ability to simulate precisely the fracture processes in the base friction model. The base friction force acting on the model elements is one of the most important factor in the base friction model. In this paper, some formulations are presented to put the base friction force acting on circular or cylindrical elements into the distinct element method analysis. Quantitative comparisons are made between numerical results and experiments on very simple slope problems. They clarify which formulation is proper. It is exhibited that the coefficient of friction between elements can be determined through simple slope problems.

View full abstract

At a shallow covered or a soft ground tunnel, the pre-lining method will be applied to excavation in order to improve face stability and to prevent ground surface settlement.
The authors are trying to clarify the mechanism of the pre-lining method by means of model experiments and to establish reasonable design methods for pre-linings. As a result of the experiments, it was confirmed that the effects of pre-linings such as improvement of face stability and less settlement mainly depend on the degree of restriction by pre-linings against vertical stress relief at the crown of the tunnel within the range of excavation. The authors also proposed that the efficiency of pre-linigs as the tunnel support should be evaluated by “compound stiffness”, which consists of the ground arch and pre-linigs around the tunnel, rather than by stiffness of the pre-lining itself.

View full abstract

In the construction of embankment with high water content cohesive soil, placing horizontal drainage layers are effectiveness for stabilizing the embankment. However, analysis method for the design has not been established enough. In this paper, the analysis method of drainage effect is proposed. Its effectiveness is proved by comparing field observation data and analysis results, and the effect of some design condition on the drainage effect are investigated based on some analysis results. Additionally, simple equation to evaluate the requested permeability for horizontal drainage is proposed. In the equation, requested permeability is evaluated from placing condition of horizontal drainage and permeability of fill material. Its effectiveness is proved using 8 kinds of field observation data.

View full abstract

This paper describes the results of the experimental studies on deformation modulus of the clay which is related to energy dissipated in specimen during application of repeated loading. The specimens after application of repeated loading were cured in two different ways, the one is under undrained state, the other is under drained state in order to find the difference in recovery phenomenon between with and without reconsolidation.
As a result, it was made clear that recovery in deformation modulus due to reconsolidation can be separated from that due to thixotropy.

View full abstract

Liquefaction of a Pleistocene Tokyo formation sand layer in Edo era was confirmed by a series of investigations in the ruins of Yotsuya-Gomongai of Edo castle located at Shinjuku, Tokyo. In this paper the liquefaction resistance of the sand layer of the site was compared with the layer around the site. The study was carried out using the following procedures: 1) statistical analysis of SPT N-value around the site, 2) Swedish sounding in situ, 3) comparison between tested resistance by undisturbed sampling and estimated resistance of the layer. It was concluded that a low-liquefaction resistance part exists in relative abundance in the upper part of the Tokyo formation sand layer.

View full abstract

The Statnamic load method has been developed for an alternative to the conventional static pile load test. The Statnamic test is one of rapid load tests where loading duration is within about 200ms. The Statnamic test has several advantages such that no reaction beams and no reaction piles are required, and time for testing is very short compared to the static load test without of a delay of pile construction work. However, dynamic effects including inertial effect and penetration rate effect during Statanmic load have not been fully clarified yet. This paper compares the Statnamic test results and the static load test results of various pile types, and scrutinizes possible dynamic effects of the Statnamic test.

View full abstract

Through the recent researches, significant influence of high temperature on the engineering properties of soft clay has been reported. In the present study, influence of high temperature of 75°C on the stress-strain relationship and the yield surface of soft clay is experimentally studied. The results of the study show that the yield surfaces of soft clay expand by the influence of high temperature. Analyses on the results by the yield function are made, and an equation on the stress-strain relationship is introduced and its validity is investigated.

View full abstract

By employing four 20cm- cubic granite specimens of different grain size, hydraulic fracturing test were conducted. Water was injected into a vertical hole bored normal to a rift plane of the specimen. In the two horizontal directions, 12MPa and 6MPa confining pressure were applied to the specimen. Due to water injection, a horizontal crack along a rift plane was created in the specimens having larger grains, while a vertical crack along the direction of the maximum confining pressure was created in those having smaller grains. In addition, fault plane solutions of acoustic emission indicated that microcracks in the specimens of larger grains were of shear type while those of smaller grain were of tensile type. These results demonstrate that grain size considerably influences the orientation of crack extension and the mechanism of microcracking in hydraul fracturing of granite.

View full abstract

It is in general that soil is classified into sand and clay in practical design. The effective stress analysis is applied to the former soil and to the latter soils, the total stress analysis is used. In sites, however, there often exists soil intermediate between sand and clay, which is called “intermediate soil”. The intermediate soil always bothers engineers how to determine its soil parameters. Laboratory and in situ tests, such as Cone penetration test (CPT) and Dilatometer (DMT) were carried out at Ishinomaki, Miyagi prefecture to know characteristics of intermediate soil. It is found from the present study that the residual effective stress in the specimen is very small due to stress release during the sampling process. Therefore, the unconfined compression test, which is the present standard test for evaluating strength of intermediate soil, measures very small shear strength. Instead of this test, recompression test, where in situ effective stresses are applied to the specimen, is effective to evaluate the strength.

View full abstract

In this paper, as the basic study to analyze the deformation of “ballast”, a track component of ballasted track which is composed of crushed stone, regarding its part as an assemblage of coarse granular materials, the application method of discrete analysis treating the problem including discontinuous boundaries to cyclic deformation of coarse granular materials was discussed by simulating triaxial tests of railroad ballast with DDA (Discontinuous Deformation Analysis). As a result, it was revealed that some new guidelines for the application method of DDA were indicated, and also quasi-static performance of railroad ballast is discussed in terms of fabric transformation of particle alignment.

View full abstract

The pressuremeter is mainly classified into pre-boring type pressuremeter (PBP) and self-boring type pressuremeter (SBP) according to the boring methods. The SBP is one of the most reliable in-situ shear test method which can minimize the effect of bore hole wall disturbance and stress release. In this paper, some practical problems of SBP tests, such as the effect of excess pore water pressure generated at the boring process, were evaluated based on a series of SBP tests in a normally-consolidated clay ground, and the lateral earth pressure at rest and the shear moduli obtained from SBP were compared with those of some other in-situ and laboratory test methods including PBP, dilatometer, unconfined compression tests etc.

View full abstract

Unconfined compression tests have been widely used so far in spite of the criticism of the use of the test results for determination of undrained strength of soft clay deposits. In view of these circumstances, the authors formerly proposed a method for predicting in situ undrained strength of clays from the results of conventional unconfined compression test with suction measurement.
In this paper, the examination and confirmation of the validity of the proposed method was performed by comparing the distributions of undrained strength obtained by the method along the depth with those obtained by in situ sounding test results.

View full abstract

A drift has been excavated by blasting in sedimentary soft rock about 140m below the surface. In-situ measurement and numerical simulation have been performed to identify the rock zone where rock properties have been changed due to the drift excavation (Excavation Disturbed Zone=EDZ). The in-situ measurement has detected the EDZ with a width of about 1m around the drift. The EDZ has lower seismic velocity and elastic modulus and higher permeability than intact rock. The numerical simulation has suggested that it is necessary to consider excavation progress, rock stress and the EDZ for precise simulation of rock mass displacement.

View full abstract

A series of tests simulating the process from sampling to unconfined and triaxial compression tests for a highly organic soil consolidated under anisotropic stress condition were performed, and the influence of stress release and mechanical disturbance of specimen on the undrained strength is examined. A practical method for predicting in-situ undrained strength from the relationship between residual effective stress and unconfined compressive strength is proposed. From the test results, it is found that the effective angle of shear resistance is not influenced by stress release and mechanical disturbance exerted on the test specimen. It is also found that strengths detemined from unconfined compression tests can be reasonably corrected to estimate in-situ undrained strengths by applying a simplified method.

View full abstract

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 series of centrifugal model tests taking into account the strain level of the backfill soils. As the results of the experiments, 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.

View full abstract

A comparative study of the Mikasa Direct Shear Test (DST) and the NGI Direct Simple Shear Test (DSST) has been carried out on shear properties of two marine clays. Samples from Ariake clay and Norwegian Drammenclay have been subjected to both types of test. An evaluation of tese test results and a theoretical considearation on the different shearing mechanisms in these testing types are presented.

View full abstract

When mudstone is employed as a fill material, the slaking or degeneration of the material often causes the engineering problem such as excessive surface settlement or slope failure of an embankment. The present study is theoretically and experimentally concerned with the settlement characteristics of compacted mudstone materials subjected to submergence, by considering the mechanical properties of compacted mudstone and the mechanism of unsaturated seepage flow. Although there remains the problem that the conditions treated in this study are strongly idealized and restricted, it has been found that the theory can explain the time history of both settlement and moisture content of a compacted mudstone material subjected to submergence. Moreover, some settlement characteristics has been revealed from the experimental results.

View full abstract

Sand and clay are typical elastoplastic materials. The behavior of sand and clay under various three-dimensional stress conditions has been analyzed by the elastoplastic models based on the t_ij-concept proposed before. These models can consider the influence of intermediate principal stress on the deformation and strength by using the modified stress t_ij. However, the elastic behavior of sand and clay has not been paid much attention.
In the present study, elastic constitutive equations for sand and clay are proposed by introducing the t_ij-concept into Hooke's law. The validity of the proposed equation is confirmed by analyzing various triaxial compression and extension tests on Toyoura sand under drained conditions. The elastic behavior under undrained condition is also discussed. It is indicated that the proposed equation with the t_ij can predict well the elastic behavior of sand in general stress systems.

View full abstract

A newly designed automatically controlled versatile triaxial apparatus with high performance digital servo motor, which is able to measure small strains in the wide strain range from 10^-6 to 10^-1, and to measure elastic shear wave velocity of clay specimens during consolidation and shear stage, was developed. After verification of the performance of the apparatus by a series of tests using a reconstituted clay, anisotropically (or Ko) consolidated and Ko rebounded undrained triaxial compression and extension tests with measurement of elastic shear wave velocity and with cyclic loading at small strain range before starting monotonic loading was performed. From the test results, the validity of the newly developed local strain measuring system was confirmed and the limit of applicability of SHANSEP method for determining undrained shear strength of undisturbed clays was clarified.

View full abstract

In order to carry out inverse analyses successfully in geotechnical and structural engineering, it is important to plan observation schemes in an appropriate way. In this study, the information flow among prior information, observation and prediction process is described based on Information Entropy introduced by Shanon which is rather widely used tool in the communication theory; two criteria to evaluate observation schemes are proposed, one is termed model parameter mutual information, and the other prediction mutual information. Some discussions are made to clarify the relationship between the proposed criteria and the conventional observation scheme evaluation criteria developed in the area of experimental design. The proposed criteria are illustrated by two relatively simple but realistic examples.

View full abstract

This paper proposes a new method of back analysis to be applied for monitoring deformational mechanism of a jointed rock mass around a large scale underground powerhouse cavern. In this method, amount of slip displacements along each joint set is treated as main unknown parameters, which are determined from measured displacement by a minimum norm solution method. The method is applied to analyze the measured displacement data for the underground cavern of the Okawachi Pumped Power Storage Scheme. The results indicate that not only general strain field, but also in-depth deformational mechanism of the jointed rock mass along with changes in axial forces in PS anchors, can be identified in a fraction of a time which used to be required by traditional back analysis methods, with reasonable accuracy.

View full abstract

In this study we determined quantitatively the properties of the frost heave, freezing rate, frost heaving ratio and temperature gradient within sample on open system and closed system. In these experiments, the sample size is approximately 6cm diameter and 2cm high, and the temperature of cold side was controlled with a certain cooling rate. It was known that freezing rate and temperature gradient changed with different cooling rate, also frost heave and frost heaving ratio were influenced by the temperature gradient. Moreover, at the case of cold side temperature was fallen with a certain cooling rate, it has been known that the frost heaving ratio can be expressed with a function of warm and cold side temperature, temperature gradient and overburden.

View full abstract

A set of field investigations was carried out for more than two years at a site of weathered granite in the vicinity of Hiroshima City to examine geological and mineralogical characteristics of weathering. Field investigations include geological survey, borehole lateral load test, cone penetration test, in-situ elastic wave exploration test, insitu density test and plate loading test. The geological investigation shows that the site weathering is characterized by several clay veins and the test results indicate that the initial value gradually deteriorates down as time goes by. The results of plate loading test show that failure pattern observed was typical of local shear failure and significant particle crushing was observed beneath the footing.

View full abstract

A model test for laterally loaded single pile embedded in sand and their 3-D FE analyses have been carried out. In the analyses the sand was assumed to be an elasto-perfectly plastic material, and several 3-D constitutive equations for sand were investigated. In each case, the stress paths of the ground were output and the interaction between the pile and the ground was discussed in detail from a viewpoint of mechanics. It is shown that the 3-D constitutive equation should be selected carefully in such analyses.

View full abstract