This paper focused on the enhancement of liquefaction strength at the precipitation rate of calcite to sand mass is approximately 2% by using urease production bacterium. This study examined the feasibility of improving the liquefaction strength by using various enzyme activity speeds with Toyoura sand. Authors used the cyclic triaxial test to evaluate the enhancement of the liquefaction strength with three types of microbes (Bacillus pasteurii isolated from land, Sporosarcina aquimarina isolated from the coast, and an enriched culture from the liquefaction disaster area caused by the 2011 Tohoku earthquake). The main findings were as follows: (1) the enriched culture from the natural foundation area can enhance calcite precipitation within pore spaces in sand based on the urease enzyme; (2) the urea and calcium source concentrations should be adjusted based on the urease activity to take the same weight of calcite by using various kind of bacterium; and (3) a precipitation rate for calcite of 2% - 3% can improve the liquefaction strength based on many kind of urease production bacterium.

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It is important to consider the influence of temperature when evaluating the frictional behavior of a single rock joint since the behavior may change due to geochemical processes which occur at the asperity contacts, such as mineral dissolution. It is thought that such chemical processes may be accelerated under certain thermal conditions. In this study, direct shear tests under a slide-hold-slide process, using granite and mortar specimens with a single natural rough joint, are performed at temperatures of 20 and 60°C. Through the experimental results, the shear strength healing can be evaluated. Moreover, the log-linear equation and the rate- and state-dependent friction law are applied to the experimental results in order to examine the influence of temperature on the shear stress healing phenomena.

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The slope failure so far has been occurred due to the heavy rainfall, and induced losses of a human life and properties produces. In order to prevent these damages, the measurement and the evaluation for the strength characteristics of the ground such as the shear strength and the angle of internal friction should be required. The direct shear box test (DST) for this has been generally used. Kim et al. (2012) reported that the result in the DST could be varied according to the difference of the opening size between the shear boxes, and suggested the Threshold-Line (TL) as a standard for the opening size. Thus, the suggestion of the opening size by Kim et al. (2012) in this study was discussed through the distinct element method (DEM) simulation. As a result, the shear behaviors obtained by the DEM simulation are similar to their experimental results. Thus, it is expected that the TL can be a standard for the opening size between the shear boxes.

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On 20th August, 2014, a series of slope failures and debris flows were occurred around city of Hiroshima , Japan due to the torrential rainfall. Debris flows took place at 107 valleys and slope failures occurred at almost 59 locations between 3 am to 4 am. This calamitous event costs 74 lives and left 44 injured. This report consists of the investigation results and considerations of the debris flows and slopes failures in the affected areas. The investigated damages were compared with the damages predicted in the field survey which was carried out to designate the restricted area and the special restricted area due sediment-related disaster. It was found that the volumes of debris flows and the damages were much larger than those predicted in the survey, and the problems of the field survey and the designation system were discussed.

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On 20th August, 2014, a series of slope failures and debris flows occurred around city of Hiroshima, Japan. The debris flows took place at 107 valleys and slope failures occurred at almost 59 locations between 3 am to 4 am., costing 74 lives and left 44 injured. This calamity was caused by the 2 hours and more continuing torrential rainfall of more than 80 mm/h intensity, which took place under the squall line formed by a sudden weather change. In this report, the considerations were made on how the present hazard prediction methods with the rainfall index were applied and worked in this disaster. The points to be improved were discussed.

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Selection of the location of monitoring of the deformation and the groundwater level in the slope is important for time-prediction of an onset of shallow landslides based on the monitoring. The analysis of the monitored data on the surface displacement and the groundwater level at different locations in sandy model slope under artificial rainfall was conducted in this study. The analysis revealed that surface displacement increased with the increase of the groundwater level significantly and the relation between the surface displacement and the groundwater level can be modified as hyperbolic. The surface displacement grew larger and maximum groundwater level was smaller at farther location from the toe of the model slope. Time-prediction of an onset of landslide based on the monitored data at different location on the model slope was conducted as following procedures. (1) To make the regression equation for the surface displacement - the groundwater level relation based on the monitored data at any time before the failure, (2) To make the regression equation for the time - the groundwater level relation based on the data until same time with (1), and (3) To combine the equation (2) to the equation (1) to derive the time - the surface displacement relation. (4) To derive the time - inverse of the surface displacement velocity from the equation (3). The equation for the time - the surface displacement and the equation for the time - the inverse of the surface displacement velocity could simulate the actual phenomena of the model slope well based on the monitored data at any location on the model slope.

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Piled raft foundation has been widely recognized as a rational and economical foundation system with the combined effects of raft and piles. However, the behavior of piled raft foundation subjected to horizontal and moment load has not been well clarified due to complex interaction of raft, ground and piles. A series of centrifuge model tests was conducted on the piled raft model and its components of pile group and raft models. In this paper, a focus was particularly placed on the influence of the vertical load of the foundation on the behavior of laterally loaded piled raft foundation. From the centrifuge model tests, it was found that the raft base pressure in the piled raft foundation enhances the horizontal and moment resistance carried by piles. In addition to the increase of pile resistance, mobilization of raft resistance contributes to higher horizontal and moment resistance of the piled raft foundation compared with the pile group foundation. The increase of vertical load of the foundation results in relatively larger settlement for both piled raft and pile group foundation. However, the increase of settlement associated with the vertical load of the foundation can be restrained for the piled raft than the pile group foundation. This relatively large settlement of the foundation secures the contact condition between the raft and the ground. Therefore, above mentioned positive effects of the raft part can be more significantly expected for the piled raft with relatively larger vertical load of superstructure.

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The frequency of rainfall-triggered landslide has recently been increasing in Asian countries including Japan. In this paper, by reflecting the past findings that weathered granite is landslide-prone geological condition, engineering properties of weathered granite have been reviewed based on the past works. And, considerations on the stability evaluation in the weathered cut slope in Phuket, Thailand have been presented. As a result, it was pointed out that in the case of relatively steep cut slopes comprising weathered granite, the combination of both the storage of water in the prominent portion of fine-grain fraction generated by weathering, which distributes in relatively shallow area from the slope surface, and the reduction in a shear strength due to increase of degree of saturation become trigger of shallow landslide.

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