It has long been difficult to differentiate the coral gravel soils when evaluating their strength because of the large variation and it has been required to resolve this issue. This has been done by means of a study focused on the drainage characteristic. As for the general soils of mainland Japan, the content of fine fraction at 50% is considered adequate for the separate point between cohesive soil and intermediate soil. However, the necessary content of the cohesive soil with “c” evaluation of coral gravel soils were found to be 70, 80, 75 and 80% for the ports of Nakagusku, Naha, Hirara, and Ishigaki. Additionally, the Plasticity Index for the same cohesive soils were found to be 35, 20, 20 and 20 for each of the four ports. Based on the research and its result in this paper and on other research in the past, the way how to differentiate the coral gravel soil that should be sandy, intermediate, or cohesive, was proposed.

View full abstract

The strength of sand improved by the soluble type of grouting decreases with the increasing distance of injection point. One of the reasons for this strength decrease is considered the dilution of grout that occurs as it fills the void of sand layer. In this study, model tests are performed to clarify the dilution at the time of grouting on the basis of the theory on advection and diffusion. Measures used were: 1) verification of the theory by one-dimensional model grouting test, 2) consideration on the application of a numerical model for soluble type grouting, and 3) verification of the model at a field test. As a result, it was found that the diffusion coefficient at the time of grouting, which was measured in the field test, was greater than the one from the one-dimensional model test. However, it was confirmed that the proposed model could explain the dilution of grout in grouting process.

View full abstract

Buffer material as an engineered barrier system for high-level radioactive waste disposal is expected to seal initial cracks or gaps within it during re-saturation process. Since the self-sealing ability is based on swelling behavior of the buffer material, estimation of swelling characteristics during re-saturation process is very important. In this paper, the theoretical model for evaluating swelling characteristics of saturated buffer material is expanded to unsaturated media, and is applied to coupled thermal, hydraulic and mechanical model. After the verification by using a series of swelling experiments, it is applied to the heating test conducted at Kamaishi mine and its applicavility is examined.

View full abstract

The dynamic behavior of a group-pile foundation with inclined piles in loose sand has been investigated by conducting dynamic centrifuge model tests. And the dynamic features of it have been evaluated. In this paper, the centrifuge model tests are simulated by dynamic finite element analyses, in which the deformation of the piles is carefully investigated, and those analyses are compared with the current method such as separated method and seismic deformation method, and then it was found that dynamic analyses are effective for the seismic design of group-pile foundation with inclined piles. Moreover the relations between the dynamic behavior of group-pile foundation and the design parameters such as pile spacing and inclination angle of pile were investigated by dynamic analyses.

View full abstract

In recent years, the developement of appropriate methods to evaluate the imminence of the slope failure of rock mass appropriately and simply is urgently reruired. In this study, a estimation system of rock slope failure in the coastal areas of the Sea of Japan in Hokkaido using QT2 (quantification theory type 2) and SOM (self-organizing maps) are proposed. SOM analysis identifies the data characteristic and selects unique points. QT2 analysis examines what kind of topological and geological factors are attributed to a slope failure. Therefore, the reliability of these stability evaluation of rock slope was improved by combining QT2 with SOM.

View full abstract

This paper describes the effective utilization of mudstones as a banking material. Mudstones are produced in abundance from construction work. Compaction tests, unconfined compression tests and triaxial compression tests were performed on mudstone to investigate the effects of inundation and slaking after compaction on mechanical properties of compacted mudstone. It is found that the failure envelope after inundation of compacted mudstones may be divided into normally consolidated and over-consolidated states using the compaction yield stress. In addition, the compaction yield stress can be readily evaluated from the dry density of mudstones.

View full abstract

The filtration of the red soil muddy water by filtration type basin of sedimentation soil is used as one of the red soil outflow prevention method in Okinawa Prefecture. This method is a main method widely used in many fields, because it is advantageous for workability and economical efficiency, if the site can be ensured. There are two problems on this method that the function of the filtration lowers by the transmission of red soil muddy water and the term which can ensure the filtration ability with the sufficient permeability is indefinite. The following are described in this study: Latest experimental result and design method of new filtration type basin of sedimentation soil capacity using the result.

View full abstract

Cyclic Undrained Triaxial Tests were carried out, after performing K₀-consolidation to fine containing sands, which had diferrent fine content (Fc) and fixed initial relative density. Consequently, it turned out that, as for the size relation between the initial shear stress and the amplitude of cyclic shear stress, the behavior of K₀-consolidated sandy soil were classified into liquefaction, cyclic softening, and no-failure. And the result of arranging these behaviors using the index (SRR), which indicated the degree of the reversal to the extension side of cyclic shear stress, produced that SRR was by the volume of Fc. Furthermore, it turned out that the failure form according to the specified number of cycles, in the relation between cyclic shear stress ratio and number of cycles, was classified as liquefaction or cyclic softening by Fc, and changed the treatment of liquefaction strength evaluation.

View full abstract

The performance-based design of road embankment on soft ground is scheduled to be introduced in the near future. In this paper, an applicability of an elasto visco-plastic soil/water coupled FEM to the performance-based road design is discussed. FEM analysis is carried out to simulate the long-term stress-deformation behaviour and the stability during construction of the actual road embankment on the soft ground. The analyzed and measured results agreed well and the maintenance cost estimated by the calculated residual settlement also agreed with the actual cost. Some case studies to select the optimum countermeasure for soft ground considering the road performance and minimum life-cycle-cost are carried out. One example of the performance-based design using FEM is shown through the case studies.

View full abstract

This paper concerns geotechnical utilization of coal ash. First, definition and evaluation method of consistency for coal ash is proposed based on laboratory investigation. Condition of coal ash depending on amount of mixed water is classified into three categories and the two boundaries are defined based on knowledge of ceramics engineering and concrete engineering. These boundaries are evaluated easily by conducting the fall com test with 20g com. Its application for estimating mechanical properties is also examined. Initial void ratio and compression index of coal ash specimens prepared by water sediment method correlate closely with index consisted with the proposed consistency limits. Proposed evaluation method of consistency and the application for estimating of mechanical property can be useful in the case of using coal ash as reclamation material.

View full abstract

Highly impermeable geomaterials which will be used in coastal waste disposal sites can be constructed only by pumping installment. For this reason, the fluidized materials of high water contents must satisfies the requirements of no water pollution and no discontinuity under water as well as high impermeability at the time of their installation.
Based on a series of experimented work by the use of sea bed clays mixed with bentonite or sand, a new method to define the mixture design of them has been proposed on the basis of only the liquid limit of the mixtured material.

View full abstract

Considering that water films formed beneath low permeable layers in liquefied sand have a great influence on lateral flow mechanism, shaking table tests for saturated sand slopes are carried out. In a saturated uniform sand, flow deformation occurs almost exclusively during shaking, while in a sand slope with a sandwiched silt arc, large flow deformation occurs like a rigid body by the water film effect in the upper layer after shaking even under small accelerations. Results of energy analysis during the post-shaking flow reveals that the shear strength exhibited along the slip surface passing through the water film decreases to 20% of that of uniform sand. It takes non-zero value presumably due to the roughness of the water film.

View full abstract

As one of the quiet rock fracture methods, a slide-type hydraulic rock fracture machine was made on a trial basis. This machine was able to add a concentrated load in the pressure hole using a wedge in four directions perpendicularly for obtaining an effective fracture.
Using this machine, the effect of empty holes and size of pressure plate on rock fracture was investigated by theoretical analysis, laboratory and field tests. Results of the investigations showed that empty holes are effective to reduce the force required for fracture. It was also found that the force and energy required for fracture decrease with increasing size of the pressure plate.

View full abstract

In order to build up the construction technology of buffer for geological disposal of radioactive waste, it is necessary to investigate the compaction characteristics of mixture material of bentonite and silica sand. From the results of static compaction experiment, relation between specifications of buffer and compaction characteristic was investigated. And the particle action mechanism during compaction was investigated by comparison between dynamic compaction and static compaction, and by microscopic observation. As results, the influence factors on compaction characteristics of buffer material are shown from the viewpoint of particle action mechanism.

View full abstract

It is important to analyze quantitatively the micro-structure of clay and to correlate the results with the mechanical behavior of clay. Studies are conducted on consolidated Illite and DL-soil samples, and the Color Laser 3D Profile Microscope is used. Sm-value, Fractal dimension and Fourier transformation are employed for the analysis. The results from these quantifications show some influence of measurement conditions. Thus, the measurement conditions must be carefully selected. The results of the analysis indicate the difference of the particle size of the samples and the change of the micro-structure of the samples before and after the consolidation, especially by Fractal and Fourier methods.

View full abstract

The paper presents a photogrammetric system with a digital camera as a precise measuring tool for the monitoring of slope stabilities. The least squares solution with a pseudoinverse method, which has the advantage of the flexibility of measurement, is introduced by both of mathematic and geometric concepts to transform two dimensional digital image coordinates into three dimensional object space coordinates without the incorporation of control data. In the paper, experiments have been also conducted to quantitatively examine the accuracies and precision of this solution, and the results show that this measurement system has high potential applicability in deformation monitoring of a slope.

View full abstract

Field and laboratory tests were conducted to investigate the degree of strength variance on large-scale artificial ground. The ground was constructed by pneumatic flow mixing method, in which dredged soil and cement are mixed in a pipe during transforming. Stability of monitoring and controlling system on cement-water ratio of treated soil was observed. It was also observed that the effect of the transforming distance on the strength variance was negligible as far as the distance exceeds around 650m. However there were relatively large influences of non-homogeneity of dredged grounds, though the area of the dredged ground was divided to have similar physical properties of soil so that the quality control was significantly improved. The effects of placements of treated soils in water, sampling methods and laboratory test conditions were also discussed.

View full abstract

The countermeasure of L type retaining wall to frost heave occurred in backfill was studied. Test wall was installed in a filed of Kitami institute of technology. The wall consists of following three sections, 1) back filled with frost susceptible clayey soil, 2) using thermal insulation material, and back filled with frost susceptible soil, 3) backfilled with frost-unsusceptible soil. From Nov. 1999 to April 2002, the freezing lines, displacement of wall, and so on were measured. The effectiveness of replacement method and insulation method was verified through the measurements. Finally, a method to determine replacement range was suggested by using computer numerical simulation of freezing line in backfill.

View full abstract

In the design for buffer and backfill materials for repositories of high-level nuclear waste, we must choose the adequate bentonite among many kinds of bentonite in the world. To select the adequate bentonite, we have to get the fundamental properties such as seepage and swelling of many kind of bentonite. To solve this problem, the study proposed the new simplified experimentation using measuring cylinder and new analysis method for seepage and swelling properties. We investigate the validity of new method by the laboratory tests using five kinds of bentonite. Furthermore, this study describes the influences of water-chemistry to the seepage and swelling properties of bentonites on the basis of the experimental data obtained by new method.

View full abstract

Difference in the micro-structure of clay can be shown qualitatively by the electron microscope, but there are few researches that have evaluated it quantitatively. Studies are conducted on Tokyo Alluvial Clay, and the Color Laser 3D Profile Microscope was used. Fractal dimension and Fourier transformation were employed for the analysis. After the measurement and analysis on the undisturbed and reconstituted samples, the present study indicate quantitatively the difference in the micro-structure of clays. Changes in the micro-structure of clay by the consolidation are also detected. Moreover, difference of the results by the sample preparation process between air-drying and freeze-drying is discussed quantitatively.

View full abstract

Recently, we have a very difficulty to prevent the leakage of the old earth dams because of the shortage of suitable impervious embankment soil. Authors suggested yet the preventing method of leakage of the old earth dam by utilizing the existing embankment soil of the dam. This method is the mechanical stabilization by mixing the embankment soil obtained from the existing dam that needs to prevent the leakage and the mud soil in the reservoir. This paper represents the results of field test performed to investigate the applicability this preventing method.

View full abstract

There are several themes in the mechanical behavior of a rock-fill dam. They are the stress concentration at the filter zone, the drop of the stress at the core zone, the highly sophisticated analysis method of the earthquake resistance of a rock-fill dam, and the new design method of a concrete-faced rock-fill dam (CFRD). In this study the stresses and strain behavior observed at the 4 rock-fill dams were compared with each other and analyzed from an overall viewpoint. The authors believe that the present investigation could provide useful information to dam design method and sophisticated analyses of dam body behavior.

View full abstract

The sludge discharged from sewage treatment plants is disposed of as follows: polymer flocculant is added to the sludge, which is then dehydrated to reduce volume, and then incinerated and buried in controlled landfill sites in the form of incineration ash.
This study examined whether the sewage sludge ash could be used as a soil-stabilizer component, that is, whether the backfill soil obtained as mentioned above meets the applicable strength and environmental quality standards for soil. As a result, the potential of the sewage sludge ash was confirmed.

View full abstract

Most of irrigation reservoir dams were mostly accumulated with a muddy soil in reservoir that caused the pollution and the shortage of reserved water. This muddy soil generally is high-water-content and very soft clayey soil. In order to make efficient use of such a problematic soil as embankment soil, we have developed a new type method to repair the damaged embankment by means of the stabilized muddy soil with cement stabilizer. We representes the case study of sloping core zone constructed by cement-stabilized muddy soil that applied this method to reinforce the steep and high embankment of an old small earth dam, and also shows that the sloping core zone with the zoning in strength becomes a very useful method to reinforce the steep and high embankment.

View full abstract

The compaction criterion of mudstone materials is examined based upon some experimental results of the deformation characteristics due to submergence. It is shown that the critical air-porosity is reasonable to be adapted as the criterion. Moreover, since there exist certain relations between the critical air-porosity and the material properties such as slaking, breakage and water absorption of mudstone, the critical air-porosity can be easily estimated by using the relationships.

View full abstract

Issues on the basis of foundation design are discussed in conjunction with partial factor format, i. e. design approaches and the estimation of characteristic values of geotechnical parameters, for the future development of foundation design codes. First, it is examined which approach is more suitable for foundation design, material factor approach or resistance factor approach, and it is concluded that the later is better from the practical point of view. Second, a common procedure from a ground investigation/testing to the determination of design geotechnical parameters is proposed. The reliability of geotechnical investigation should be considered in the stage of the evaluation of characteristic values.

View full abstract