[in Japanese]

View full abstract

In a regional ground water analysis by using a quasi three-dimensional finite-element method or the like, it is important to determine the spatial distribution of transmissivity T. Developed in the present study was a system for estimating the coefficient of permeability based on the density measured in situ with a split-spoon sampler with built-in tube. The water levels determined by numerical analysis based on the permeability coefficients estimated by the system were compared with measured water levels to ascertain the validity of the system.

View full abstract

Recent large earthquakes, such as Kocaeli in Turkey and Chi-Chi in Taiwan, produced earthquake surface fault, which damaged many near-by structures due to displacement. It is thus required to consider such damage due to faulting in design structures since faulting is not a subject of design codes. The objective of this paper is to qualitatively evaluate the influence of vertical fault movements, in order to clarify the faulting mechanism as a fundamental element for establishing design codes. A series of model experiments are being made for this purpose. Surface deposit in which a fault propagates is modeled as a set of aluminum rods. As well as deformation of rods are measured, stress acting on the base are measured. It is shown that a large moment works at the tip of the fault, which drives the fault propagation. It is also shown that depending on the fault type, the fault propagation changes and there is some common tendency for it. Although these results are for model experiments, they will serve as basic findings for faulting.

View full abstract

On the vacuum-induced consolidation method which is one of the soft ground improvement methods, resolved air and gas are pumped out mixing with ground water through prefabricated vertical drain (PVD) and horizontal drainpipe due to vacuum pressure. This method is the accelerated consolidation method. It is necessary for the practical design to evaluate the increment in consolidation pressure suitably. Therefore it is one of the most significant problem to make clear the mechanism that the flow pattern and pressure in PVD are changed in the cause of air and gas. A sample pumping test system is developed which simulates the condition of flow in cylindrical vertical drain, in which can be controlled the shape and volume of air, measured the pressure and visualized the behavior of flow, in the riser pipe under the negative pressure. This paper discusses the flow pattern and pressure in the riser pipe. Practical parameters to evaluate above phenomena are proposed, and the validity of parameters is confirmed based on the experimental results.

View full abstract

Though many researches on the hydraulic fracture initiation pressure have been done for cohesive soil specimens, the hydraulic fracture phenomena in actual grounds are different from those in the laboratory. The main reason is that the extension of hydraulic fracture in actual ground may become very large. Therefore, we investigate hydraulic fracture initiation pressure and the fracture extending pressure in a field test by well bores. The extending speed of the hydraulic fracture was calculated from the injection rate of slurry into the hydraulic fracture space. The main objective was to investigate hydraulic fracture problems when the slurry type shield is used to excavate through cohesive soil ground. Therefore, in addition to the well bore test, hydraulic fracture experiments using a model slurry type shield were done. From both experimental results, the hydraulic fracture situation for an actual slurry type shield could be predicted.

View full abstract

Bifurcation phenomena of initially homogeneous elasto-plastic specimen under uniform compression are numerically investigated. The finite strain, associated, strain hardening Drucker-Prager plasticity model is employed as a material model. Deformation of the specimen remains uniform on the primary equilibrium path, whereas non-uniform deformation modes arise due to bifurcation. We carry out several numerical analyses for bifurcation modes and post-bifuraction behavior without imposing initial imperfections, and show that diffuse bifurcation modes are one of the important factors for the occurrence of localized deformations. We also discuss the numerical results of path jumping phenomena.

View full abstract

This study reveals the characteristics of the bearing opacity of spread foundation on improvement ground of soil cement mixed with plastic chips. Fist, the unconfined compression test is conducted in order to confirm the improvement of soil cement's elements. Next, the laboratory bearing capacity test is done to clarify the characteristic of the bearing capacity. As the result of these tests, it is found out that, in the case where plastic chips are included, the failure mechanism of the improvement soil cement ground changes from the brittle failure mode to the ductility failure mode. Furthermore, these failure mechanisms are assumed based on the test results, and the equation for evaluating bearing capacity is formulated using the velocity field method.

View full abstract

In order to make clear reasonable executive conditions of steel fiber reinforced high-strength shotcrete (SFRS) constructed in a squeezing tunnel with time dependency, a numerical analysis has been conducted, by taking velocity of tunnel face progress, elasto-plastic behavior of steel supports and time dependency of strength of SFRS into account. It has been recognized that SFRS is a reasonable primary lining for a tunnel with sever geological conditions. Especially high strength at early stage of its execution and the toughness after its yielding contribute to the safety construction of a squeezing tunnel with time dependency.

View full abstract

After the emplacement of engineered barrier system (EBS), it is expected that the near-field environment will be impacted by phenomena such as heat dissipation by conduction and other heat transfer machanism, infiltration of groundwater from the surrounding rock into the EBS. This report describes the results on measurement of isothermal water diffusivity and thermal water diffusivity in compacted bentonite and the results on comparison between measured and theoretical calculated properties. The results indicate that the Darcy's low and Philip & de Vries model are applicable to estimating the isothermal water diffusivity and the thermal water diffusivity in compacted bentonite.

View full abstract

The objective of the present paper is to investigate the distribution of the seismic frequency and the cause of the incidence of the disaster zone in Kobe district by Hyogoken-Nambu earthquake with Kobe Jibankun-the geological information database. The geological data of the secondary wave velocity and the others for the seismic frequency analysis are the pasts of the data that are collected in Kobe Jibankun. As the result of the analysis, the seismic frequencies that were observed correspond mostly to them that were analyzed by the method of the seismic frequency analysis, and by drawing the comparison between the distribution of the seismic frequency that was analyzed by it and the distribution of the wooden house damage in Kobe district, and the correlative seismic parameter relative to the wooden house damage was revealed, and it was clear that its ratio was rising suddenly while the parameter became more than the certain value.

View full abstract

This study highly focused on the methods using equation for estimating the compacted density of granular soils with oversize particles, and several equations indicated in past studies were explained. They were compared and examined in detail based on the data measured in the past, and the practical effectiveness and fitness were evaluated. Consequently, the equation proposed by Fukumoto was proved to be adaptable in good accuracy for any granular soils and most practical.

View full abstract

Recently developed geocomposite has sandwiched structure of woven fabric in between both non-woven fabric and has over the tensile strength of geogrids of woven fabrics and also having the drainage effect of non-woven fabrics. However, current design methods of non-woven fabric-reinforced earth fills have considered the drainage function only. Therefore, this paper propose a new design method of earthfill structures considering the reinforcing effect together with strength increase of the volcanic loam caused mainly by drainage.

View full abstract

This paper describes experimental studies for pile tip protections of bored pile by use of Jet Grout Method that was developed for the ground improvement. The pile tip protections were made in the artificial sandy ground and all of them were taken out in order to investigate their strength and failure mechanism through the loading tests. The adequate mixture condition and jetting quantity of the cement slurry to get the required strength were discussed. In addition the differences of the protection shapes due to the quantity of jet water and moving speed of jet rod were examined. The equations for estimating of protection diameter were proposed and its reliability was confirmed.

View full abstract

Roller compaction tests have been carried out to investigate the reliability of the roller response method for the quality control of soil compaction. In the tests, the acceleration of a vibratory roller has been measured for various conditions of the ground, such as types of soil, density and water content. The results of tests made it clear that it is generally difficult to evaluate the density of the compacted soil uniquely from the roller response because it is much affected by the type and water content of soil. The tests results also indicated that the possibility of the roller response method for evaluating the stiffness of the compacted soil uniquely. The application of the method to construction in soil compaction was discussed with knowledge obtained through the tests.

View full abstract

The liquefaction behavior of the reclaimed land of Kobe artificial island was examined using on-line test. The array observation site in the Kobe Port Island at Hyogo-ken Nanbu Earthquake in 1995 was modeled as the four lumped mass system. The top layer above water level and the forth layer of alluvium clay layer are modeled by the hyperbolic model. The second and third layers in the reclaimed layer are directly modeled by the elementary test. As the result, it was proven that the liquefaction of the reclaimed land is significantly affected by the shear strength of the alluvium clay layer. The results obtained from on-line test showed good agreements with the array record.

View full abstract

For earthquake resistant design, especially against seismic motions, it is very important to estimate ground surface motions during earthquake. It is well known that equivalent linear method cannot be applied easily to seismic response analysis in cases of strong seismic motions with severe nonlinear behaviors. However, this method may be useful in practice if its applicability comes more extended with good precision to strong seismic motions of ground. In the study, shear strain levels and number of cycles of loading, which may have effects on modulus and damping factor of dynamic deformation property of soil, have been examined with the data obtained by cyclic deformation test using undisturbed soil samples. Then, the conversion ratio from maximum strain to effective strain used to decide the modulus and the damping factor in the equivalent linear method can be given simply in an expression of the strain amplitudes and the number of cycles of the seismic motions. The proposed expression in the method has shown good applicability to simulate the vertical array records of seismic observations at five sites.

View full abstract

In order to estimate the deformation behavior of natural sediments, the method with resistivity measurement was examined. From resistivity measurement, it is possible to obtain non-destructive data of sediments. The experimental results showed that the resistivity of natural sediments changes with the structural change due to loading. Furthermore, it was found that the failure of natural sediments could be predicted from the resistivity. Therefore, it is possible to predict the change in mechanical properties and the behavior of soils from the resistivity measurement.

View full abstract

High water-content flowable fill often utilized as a back-fill material for foundations, buried pipes, etc. in urban areas, is investigated with a special emphasis on cyclic loading effect due to strong earthquakes. As a basic step of the research, only kaolinite clay is used for slurried soil mixed with cement, yielding the following major findings. The soil keeps its original undrained strength even after cyclic loading with high stress amplitude, but deformation modulus tends to decrease with the increase of cyclic loading amplitude. Consolidation yield stress which is dependent on the cement content and slurry density has a great effect on its mechanical properties.

View full abstract

The region size to be treated by the 2-dimensional finite element method is one of the serious issues in Geotechnical Engineering since the simulated value of displacement strongly depends upon the depth of the allocated domain. In this paper, the reason for such a fact is firstly clarified by using the 3-dimensional boundary element method and some numerical examples of the tunnel excavation are illustrated to show how the domain size affects the results. Finally some remedies for the problem are proposed by assuming the oaring elastic modulus with the depth.

View full abstract

2-D computer simulations for the longterm field experiments were carried out to determine a possible range of ground freezing around a multi-anchored retaining wall. Temperature fields were calculated on several shapes and sizes of walls. Simplification was made for heat transfer calculation on material constants of soil, such as thermal conductivity, heat capacity. The depth and shape of freezing front was determined the required range for soil replacement to protect walls against frost heaving.

View full abstract

This paper aims to develop a new prediction method of rock mass stability, which is useful in a multi-step excavation such as cavern construction, based on the results of back analysis to model out inhomogeneous rock mass behaviors during excavation. Assuming the Duncan-Chang non-linear elastic relationship for rock masses, its parameters can be determined from the results of back analysis applied during excavation and strains at the stage of further excavation can be properly estimated so as to assess rock mass stability. This method is applied to the actual cavern construction problem and the results suggest that this indicates an excellent capability to predict more reasonable strains for further excavation steps at the early stage of cavern excavation such as an arch portion.

View full abstract

A rational design method for drainage pipes buried under high fills that considers the mechanical properties of fill material, backfill material, and pipe reasonably was proposed. The method was constructed by an FE elastic analysis that was validated by comparison with extensive series of centrifuge model tests. The method provided two types of design charts for practical applications to predict vertical deflections and maximum bending moments of pipes reasonably: one for any type of pipe that behaves as linear-elastic body, and the other for HDPE (high density polyethylene) pipes that behave as non-linear elastic bodies. The proposed method can be applied for almost all field conditions involving extremely high fills with heights up to 100m that current design standards do not specify.

View full abstract

The strength of cement-stabilized soils depends on many influencing factors and in particular, the mechanical properties change for curing time due to a chemical reaction of cement. It is therefore important to investigate those influences on the deformation-strength properties efficiently. The Falling Weight Deformation Measurement apparatus was developed for measuring deformation modulus of cement-stabilized soils as a nondestructive testing. In this study, this apparatus is applied to soft clay samples with different water content, cement content and curing period. The deformation modules of the cement-stabilized soils at various mixing condition is predicted from the change in the deformation modules for early curing time.

View full abstract

The purpose of this paper is to characterize seepage and dying properties of light weight soils with air foams using industrial X-ray CT scanner. A series of water absorption test and drying test were conducted using in-situ light weight soils which were sampled at the trial construction site of new Kumamoto seaport, Japan. A series of CT scanning for those specimens during the tests were also conducted for along period and the effect of air foams for seepage and drying was evaluated. Finally, the effectiveness of industrial X-ray CT scanner in geotechnical engineering was confirmed based on those results.

View full abstract

In order to utilize mass of oyster shells for a partial substitute material for reclamation, we investigate the undrained shear characteristics of dredged sludge mixed with oyster shells by tri-axial compression test and numerical analysis based upon the mathematical homogenization. The following conclusions can be obtained from this study. It is verified that the shear strength of dredged clay is improved by mixing with oyster shells. The increase of the undrained shear strength is almost proportional for mixing rate (0-80%) of the oyster shell, and it is independent of consolidation stress (49-98kPa). And, it was guessed that the structure of the oyster shell in mixed soil complicatedly changed from stress-strain relationship and pore water pressure generation characteristic in proportion to the consolidation stress, oyster shell mixing rate, and the shear strain level.

View full abstract

In order to investigate the effects of concrete plug treatment on the stress distribution in rock foundation of gravity dam, the authors carry out the gravity dam modeling tests in consideration of the location of a fault and the depth of plug. Based on the experimental results, it is confirmed that the stress distribution is largely affected by the location of a fault and the depth of plug. The effects of plug installation are 1) to enlarge the area of dam base and to distribute the concentrated force from dam body, and 2) to restrict the deformation of the foundation around the fault and to normalize the stress distribution. The stability of foundation models is examined by shear friction factor and the calculated results are compared with the model test results.

View full abstract

The difference in microstructure of two Pleistocene clays is studied. Osaka bay clay and Kyoto clay consist of the same minerals, belonging to the Osaka Group (Osaka bay clay is Ma11, and Kyoto clay is Ma4). According to the series of observation by SEM, it is known that the content of Diatom of Osaka bay clay is much larger than that of Kyoto clay. The change of micro pore size distribution due to one-dimensional consolidation was studied by a mercury intrusion porosimeter. The pore size distribution of Kyoto clay changed sensitively with the increment of consolidation pressure, however, in the case of Osaka bay clay, the change was not so clear as Kyoto clay. In the final consolidation pressure of 10MPa, the pore size of Kyoto clay was smaller than 0.1μm, while that of Osaka bay clay ranged between 0.01μm and 0.3μm. The reason of this difference is related with the content of microfossils such as Diatoms.

View full abstract

The one-dimensional compression test, single particle crushing test and observation by microscope were carried out for four kinds of crushable soil and two kinds of silica sand. The particle roughness and single particle crushing strength variability of crushable soils were larger than that of silica sands. It was proven that the yield stress of the crushable soil was lower than that of the silica sand. The yield stress was shown to be related at d₅₀ single particle crushing strength. It was further shown that the curvature of a compression curve was dependent on the variance of single particle crushing strength.

View full abstract

A series of triaxial compression tests on various sizes/shapes of Toyoura-sand specimens is conducted to demonstrate the dependency of their shear and deformation properties on their size and shape. A positive size effect on the size of the specimens has been observed to indicate that the strength of sands interpreted as the representative material property could be much stronger than that observed during laboratory tests. Different shapes have led to different bifurcation modes and, in turn, to different shear and deformation properties. For example, diamond patterns are observed for specimens with the shape ratio of 1.0, while distinct shear bands are observed for those with the shape ratio of 2.0.

View full abstract

Bentonite is attracting greater attention as buffer and backfill materials for repositories of high-level nuclear waste because these materials must have high swelling property and low permeability. To contribute the design of buffer and backfill materials, this study investigated the swelling properties of sand-bentonite mixtures, of which bentonite contents are within 5-100%, and four typical kinds of bentonite produced in Japan and the USA. The experimental works clarified the influence of bentonite-content, dry density, montmorillonite-content of bentonite and excangeable-cation-compositions upon the swelling characteristics of materials. Moreover, it was found that the authors' parameter “Swelling volumetric strain of montmorillonite” can easily evaluate the maximum swelling pressure and the maximum swelling strain of sand-bentonite mixtures and various kinds of bentonite at various dry densities and bentonite contents.

View full abstract

The effect of the overburden pressure during curing on the unconfined compressive strength of cement-stabilized soils was examined using a newly developed apparatus, which could apply an overburden pressure below 150kPa to a cement-stabilized soil under an one-dimensional consolidation condition. The test results showed that the unconfined compressive strength of the cement-stabilized soil increased linearly with the increase of overburden pressure. The cement-stabilized soil cured under the overburden pressure showed a brittle shear behavior as compared with that cured soil under no overburden pressure. Furthermore, scanning electron microscope observations clarified that the cement-stabilized soil cured under the overburden pressure had a very stiff microstructure.

View full abstract

It is an urgent task in Japan to revise structural design codes in order to meet the performance-based criteria and the international code harmonization. To do this, a new design code based on the reliability principles has to be developed. This study aims at establishing the partial factor design format for harbor structures. Reliability assessment of existing anchored. sheet pile walls is firstly performed in terms of overall stability and failures of the anchors and the wall, taking account of uncertainty of soil parameters. The first-order reliability method (FORM) is utilized to evaluate the reliability as well as sensitivity of random variables involved. Based on the result thus obtained, partial factors are set within the framework of design value method. Finally, the structure designed based on the proposed partial factors is found to have the same degree of reliability as specified.

View full abstract

A methodology is presented in which four DEM parameters are identified from back analysis of rockfall trajectories observed in field rockfall tests or traced by site investigation of natural rockfall occurrences on a slope. The proposed method, though in an indirect manner, can evaluate the parameters taking into account the effects of slope deformation and/or collision between falling rock and vegetation on the slope. A number of laboratory rockfall tests results and an in-situ test result were used to verify the proposed approach. As a result, it is concluded that four parameters can be reasonably determined from back analysis of the trajectories of falling rocks.

View full abstract

The part of the inhabitant near the railway viaduct made a complaint about the ground vibration. Therefore, the vibration measurement was carried out installing the seismographs on the ground surface and on the viaduct. It was found that the cause of the complaint was the beat phenomenon observed in the ground vibration. By comparing the 3-dimentional eigenvalue analysis with the measurement, and by comparing the inverse analysis of the train force with the measurement, we investigated the cause of the beat phenomenon. The amplification of the ground vibration was also examined.

View full abstract

To prevent damages due to liquefaction, the silty ground was improved by sand compaction pile (SCP) method. To decide sand pile spacing, large scaled experimental work was carried out by varying sand pile spacings. The improved ground was evaluated by standard penetration test (SPT), piezocone test (CPT) and dilatometer test (DMT). These data were analyzed to estimate the liquefaction resistance by various evaluation methods, following to technical standards for port and harbour facilities in Japan (SPT); Robertson and Fear (CPT); Robertson and Campanella (DMT). It was found that the effectiveness of improvement is dependent on the content of fine-grained soil for SCP piles and that the estimation of liquefaction resistance is highly affected by the type of method used for the fine-grained soil evaluation.

View full abstract