Shirasu is a volcamic soil which is widely distributed in South Kyushu in Japan. It contains non plastic fines which was created by its fragment of coarse partic les. In this study, a series of bender element tests on Shirasu was performed with varying its fines conten t. As a result, it was observed that the shear modulus of Shiarasu was decreased with increasing the fi nes content although void ratio decreased as fines content increased. However, it was fo und that there is a unique relatio nship between shear moduli of Shirasu and the equivalent granular void ratio, in which the proper contribution factor b for fines was assumed. Based on the findings in the study, an empirical formula to express the shear moduls of Shirasu with various fines content was developed as the function of the fines content, the equivalent granular void ratio and the effective confining stress.
The flow behavior of fresh and saline groundwater mixing is complicated by their differences in density. In simulating such groundwater flow with computer software, the complex coupled process of advection-dispersion, seepage flow and density driven flow needs to be implemented. Extensive verification studies of saltwater intrusion have been done between experimental data and computer simulations, but the quality of the experimental data is questionable with regard to quantifying the concentration distribution, especially in the transition zone. A quantitative measurement technique has been developed using optical methods, which can identify the morphology an d concentration distribution of the saltwater edge.
Previous reports have clarified that the Dusty Gas Model is useful for modeling migration of chemical components in gas phase of soil. We developed a met hod of obtaining the molecular diffusion coefficient, the Knudsen diffusion coefficient, tortuosity, and the mechanical dispersion coefficient by using the Dusty Gas Model for a two-component gas system. An inve rsion simulation to obta in composite dispersion and composite gas velocity was also developed by us ing a characteristic finite element scheme for convective-dispersion transpor t and the Powell conjugate direction method. The composite dispersion coefficient and composite velocity were obtained from co lumn experiments for a two-component gas system in the gas phase of soil by applying the inversion simula tion, and the diffusion and dispersion parameters were then estimated using these experimentally derived values.
This paper proposes leachate control technology usin g H-H joint interior space as a part of steel pile sheet pipe cutoff walls in coastal landfill site from a long-term perspective. In addition, the containment and remediation performance of the H-H joint in landfill site was evaluated by seepage and advection/dispersion analysis. The H-H joint was able to perform the containment and the remediation functions by keeping the low water-level at H-H joints interior space. Moreover, th e leachate control technology using H-H joint interior space demonstrates it's pos sible to contain water-solub le toxic substances in landfill sites and remediate them.
Simple stability assessment was carried out for the rock slope which collapsed in 2007 and consists of Neogene massive pyroclastic rock. The assessment met hod is the 2-D and 3-D limit equilibrium analysis using tensile strength and tensile stress, which was developed by the authors using the centrifuge model test. As a result, safety factor obtained by 2-D analysis is about 1.0 (1.1). Safety factor by 3-D analysis becomes under 1.0 when the part of intact rock of the block is less than 5.2m and 6.9m by the Crackplane Estimation Method and the Least Crack Angl e Method, respectively. As the both figures are slightly above the figure of the real intact part (5.0m) of the collapsed block, the both methods estimate the block stability precisely and sately. In conclusion, 2-D analysis is suitable for the screening of rock slopes, while 3-D analysis is suitable for more detailed estimation of target slopes.
In this study, ion seepage tests were conducted by using fine-grained soil with permeability coefficients (k) ranging from 1.0*10-6 to 1.0*10-10 m/s. In the tests, density flow and molecular diffusion were induced by giving the concentration gradient but not the hydraulic gradient to investigate the parameters affecting the movement of fine-grained soil in an inverse problem approach. Numerical analyses were also performed to evaluate the barrier performance of the fine-grained soil. The study revealed that (1) the permeability coefficient k of a bentonite-soil mixture and the effective diffusion coefficient Dd* are dependent on effective porosity ne, (2) it may be possible to estimate the effective porosity ne of a bentonite-soil mixture and the effective diffusion coefficient Dd* with relative ease from the consistency limit and (3) there is a considerable diff erence in barrier performance betwee n a 5.0-meter-thick soil layer (barrier layer) with a pe rmeability coefficient k of 1.0*10-7 m/s and a 0.5-meter-thick barrier wall with a permeability coefficient k of 1.0*10-8 m/s.
In this research, the spatial distribution for the strength parameters of decrepit earth-fill dams, and the identification methods of the distribution are discussed. Generally, the strength of the earth-fill is predicted derived from the SPT N-values. While, in this research, the Swedish Weight Sounding tests (SWS tests) are conducted to obtain the spatial distribution of the N-values as the simpler method, and the statistical model of the N-values is determined based on the sounding test results. For this task, the MAIC (Minimizing Aka ike's Information Criterion) method is employed, and the semi-variogram method is also used to identify the spatial correlation characteristics. The spatial distribution of the N-value is identified from the sounding test results with high resolution, since the point estimations are obtained with short intervals. To interpolate the point estimated values, the indicator simulation method, which is one of the geostatistical methods, is employed. In the method, the hard data (primary data) and the soft data (complementary data) can be used simultaneously. Results from the SWS and the surface wave method (SWM), which is one of the geophysical exploration methods, are dealt with as hard and soft data, respectively. With synthesizing two results, the accurate spatial distribution of N-values can be identified.
In this research, we used frost heave test equipment to conduct a freeze-thaw cycle test and checked how the various physical properties of soil, particularly the permeability coefficient and the void ratio, changes before and after the soil froze and thawed. We employed weathered volcanic ash that has high frost susceptibility and tested the soil under tightened and loosened compacting conditions. From the test results, we confirmed that the permeability coefficient and the void ratio of compacted soil with high compaction energy is increased by the first cycle of freeze-thaw and the coefficient of permeability and the void ratio of compacted soil with low compaction energy is decreased by repeating freeze-thaw cycles. In addition, we clarified that the physical properties of the soil are changed by repeating the freeze-thaw, and finally the physical properties establish a steady state after several cycles.
A high-level radioactive waste disposal facility might be built in a coastal area in Japan from the viewpoint of feasible transportation of waste. Therefore, it is important to investigate the effects of seawater on a bentonite-based buffer. This study investigated the influence of seawater on hydraulic conductivity of three common sodium-types of bentonite and one calcium-type bentonite by the laboratory experiments. From the results of laboratory experiment, this study discussed the influence of seawater on hydraulic conductivity of bentonites from the viewpoints of kinds of bentonite such as exchangeable-cation type and montmorillonite content and dry density of bentonite-based buffer.
In order to estimate the permeable properties and pore fluid properties in the ground, survey methods using dispersion and attenuation of elastic waves have been developed. The Biot theory have been applied to the frequency-dependent dispersion data, but the influence of geological properties on velocity dispersion and the relation between the permeable properties and velocity dispersion in rock specimens have not become clear. Sedimentary rock and granite specimens were tested using longitudinal waves for the difference of velocity dispersion phenomena observed in each specimen, and we examine whether the Biot theory can be applied to observed experimental data. Moreover, we tried to estimate the permeability of the rock specimen based on the theory and show that the Biot-squirt theory can be applied to estimating rock permeability using the seismic wave dispersion characteristics.
To describe the delayed compression behavior, a system of approximately parallel e-log p relations is introduced in one-dimensional consolidation analysis. In this widely used diagram, compression index λ is commonly adopted to calculate the instant compression component of the settlement which occurs on increase of effective stress. To check the effect of secondary compression on the compression index, this paper is concerned with the relationship between the void ratio and the effective stress for the component of primary consolidation, namely the instant compression index showing the tangent of the slope angle of e-log p line. Consolidation time curves obtained from oedometer test have been compared with the result of one-dimensional consolidation analysis incorporated with two types of the compression index that include or does not include secondary compression. It is shown that the change in void ratio estimated by the traditional compression index λ includes the component of secondary consolidation and also leads to the overestimation of consolidation settlement.