The design method of earth retaining wall using the improved soil by shallow (3 to 4 m) mixing method such as Trencher Mixing Method is not established. In this study, we measured the performance and internal stress of improvement soils that have low strength and low rigidity, and we compared the measurement result and the analysis result by the finite element method. As a result, we showed that we can design it reasonably in consideration of displacement of an improved soil, deformation of the peripheral ground and rigidity of the improved soil, by applying a finite element method. We showed that this method of earth retaining can be reasonable and gentle to environment, by permitting some displacement without resisting the ground excessively.

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Experimental and numerical studies are made for investigation of structural safety of off-shore waste disposal facility of disaster wastes and removed soils contaminated by the radio-active cesium due to the accident of Fukushima Daiichi nuclear power plant. As the structural safety and the function of seawall and impervious structures must be maintained to prevent the leakage of contaminated water in wastes for a long period, the facility must be designed against the level 2 class strong earthquake. In the present study, stability of a gravity type seawall and the separated impervious structure made of double walls of steel pipe sheet piles between which are filled with artificial geo-materials are investigated. Deformation of seawall and impervious structure under the level 2 class strong earthquakes are studied by the centrifuge model test, large scale shaking table test and the numerical analysis. It was shown that the sufficient distance between the seawall and the impervious structure may keep the safety of impervious structure which must be protected from deformation. The results of shaking table tests and the numerical analysis showed that the deformations of proposed structure were within the allowable level in regard to the present construction standards.

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In this study, the predominant periods estimated from microtremor observations were compared the natural periods of surface soil layer based on boring date at 72 sites widely distributed in Miyazaki plain. The predominant periods of the microtremors H/V spectral ratio and the depth of engineering bedrock were investigated quantitatively. In addition, the relationship between the predominant periods and the S-wave velocity of surface soil layer estimated from the N-value was elucidated in Miyazaki plain. As a result, the measurement method of the natural period calculated from the law of quarter wave length has obtained reliability. A new equation has been developed to estimate the depth to engineering bedrock, based on the relationship of the predominant periods and the depth of engineering bedrock and the S-wave velocity of surface soil layer. The applicability of the proposed equation to other areas requires further research.

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The steel-made impervious walls (steel barriers) have been constructed as a landfill revetment in coastal waste landfill sites. It has been clearing the steel impervious walls to possess impervious property and durability by some field investigations and experiments in the past study. The long-term impervious properties of the joint section at the steel-made impervious walls have also been evaluated. However, these evaluations do not consider the degradation of an ingredient. The authors try to apply the reliability evaluation of degradation for the steel-made impervious walls and calculate the life cycle costs (LCC) as the standard making strategy of maintenance. In addition, the authors consider the utilization method of the LCC such as selecting the method of construction which repairs the coastal waste landfill site based on the calculated LCC.

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A large-scale slope failure of embankment, which consists of volcanic sediment, at Aizu-Wakamatsu City in Fukushima Prefecture occurred due to The 2011 off the Pacific coast of Tohoku Earthquake. Some signatures of liquefaction have been observed in the collapsed embankment. When investigating the embankment slope failure mechanism, it is necessary to study the effects of particle breakage. In this study, some static and repeated triaxial tests were conducted for the soil material sampled from the site in order to investigate the change of the particle size distribution with isotropic consolidation stress and shear stress and the effect on the shear strength characteristics due to the particle breakage. From the test results, it was revealed that the sampled soil, subjected to the effective isotropic consolidation stress of 100kPa or less, increases the particle breakage amount rapidly and the shear resistance angle is significantly reduced with the increase of the particle breakage amount. Subsequently, seismic deformation analysis was carried out for the slope failure of the embankment based on the mechanical properties obtained in the test. As a result, a reasonable analysis result was obtained by considering the calculated residual strength based on the liquefaction strength curve and the reduction characteristics of shear resistance angle due to particle breakage.

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Microbial methanogenesis occurs in diverse subsurface environments. Biogenic methane is produced during the metabolism of methanogenic microorganisms. These microorganisms have the ability to produce methane using low-molecular-weight organic acids as substrates. These substrates are decomposed from hardly decomposable organic matter present in the source soil or rocks. An in situ clean-up method of ground contaminated with such compounds has been established, incorporating the Fenton reaction, utilising hydrogen peroxide and iron compounds. In this reaction, OH radicals are produced which can decompose toxic organic matter in the soil. With the aiming at developing of the production engineering of biogenic methane gas in the subsurface environments, we have proposed a new geotechnical method, known as Subsurface Cultivation and Gasification. This approach employs hydrogen peroxide to rapidly decompose organic matter. In this study, hydrogen peroxide solution immersion tests were performed on lignite in order to characterise the structural changes resulting from oxidation decomposition of hardly decomposable organic matter. It was found that the quantity of low-molecular-weight organic acids required for the microbial methanogenesis process increased with increasing immersion time. In addition, the interior structure of the lignite mass was significantly altered in the oxidation reaction, suggesting that the microorganism habitat space could be formed inside the source material itself.

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At the end of rainy season in 2009, an extraordinary torrential rain occurred at Hofu city in Yamaguchi prefecture. The rainfall caused severe sediment disasters in the mountainous region. Slope failures occurred at more than 670 sites at the heads of streams and giant debris flows swept away houses in the fans, so that 22 people died and many houses were damaged. The streams that carried the debris flows were distributed in the region of craterous granite along the Saba River flowing south through the city. Each stream has a lot of tributaries. In this study, we investigated geometrical and geomorphologic characteristics of slope failures and the resulting debris flows based on the results of airborne laser surveys before and after the disaster. As a result, tributaries of the main stream flowed through areas where slope failure occurred, and also where it did not. Also there was a correlation between the number of slope failure occurred at the head of the stream and the magnitude of debris flow. Finally we found the geomorphologic features of slope disaster peculiar to a granite region by analyzing the area of land affected by the debris flow.

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The coral reef which spreads along the coastal line of Nansei Islands, in Japan produces the problematic soil with coral gravel of which the matrix is silt. It has been well-known for geotechnical engineering practice that to sample the high-quality undisturbed soil with coral gravel is very difficult because some pieces of coral branch are contained in silt soil and consequently its density is not large. Therefore, the soil properties of in-situ soil used as design parameters have not been accurate.
In this paper a new sampling method which was performed to challenge the above problem in Amami-Ohshima, one of Nansei Islands is explained with the geological environment and the soil properties of undisturbed soil with coral gravel obtained from laboratory soil tests.

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The following correction should be made to the original paper, Vol. 10, No. 2, pp. 225-234, “Method for Evaluating Ground Stability Considering Lateral Resisting Effects Based on Pseudo Three-Dimensional Model”:
Page 226, Eq. (2) should be replaced the new one

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