The road slope hazard, which is the occurrence rate of rock falls along the major road, in Hida region, consists of Takayama, Furukawa and Gero areas, is evaluated in this paper. This rock fall rate is estimated in two folds. First, the relative rate of lock falls is estimated by the Logit regression analysis based on the inventory data of slops along the major roads in the region which includes about 3000 slopes. The inventory data include topological, geological and geotechnical characteristics of each slope evaluated by the experts in 1996. The slopes are also classified into three categories by the experts as "measures required', "continuous observation" and "no measures required". Based on this classification, the logit regression analyses are carried out to rank the hazard of the slopes by their attributed characteristics as the explanatory variables. Once relative rate of lock falls are estimated for each slope, this rate is calibrated to the absolute rate by using the actual rock fall event records between 2004 and 2008. By these two folds estimation procedure, the absolute rate of rock fall for each slope along the roads are finally esti-mated. This study is a part of the infrastructure asset management strategy decision making program based on risk, and the information gained in this study is combined with other evaluation data for damage to propose the strategy for repair and maintenance plan of the road slopes in this region.
It is important to simulate big eqrthquake by the large soil tank on the shaking table to understand underground and structure behaviors. In this study, authors developed and examined a new investigation method of visualizing the inside of soil tank by velocity and attenuation tomography. This method is based on the previous study "high resolution geological survey by high frequency seismic wave" which is characterized by high frequency pseudo random wave. Authors improved this previous method in miniaturizing and speeding up equipment to transmit higher frequency than 30kHz and examined the effect on the accuracy of inversion caused by shortening distance between the transducer and the receiver. Our experimental result shows that this new method is useful to visualize the inside of soil tank. It also shows that interpretation of both of velocity and attenuation images is much better than only velocity image to find loose sand area.
It has been about 50 years since ground anchorages were introduced to Japan. The number of permanent anchors constructed has already reached ab out 100,000 a year. Howeve r, an increasing number of corrupted anchors have been reported recently. If th ere is a problem in the design of anchorages, one of its possible causes is the yet-to-b e-clarified mechanism of the anchors' adhesion to the bedrock, in particular. In this study, we conducted a detailed examination on the behavior of the anchor body in relation to the pseudo bedrock and examined support mechanism of anchorages. Based on its results, we suggest improvements for the designing standard of the anchorages.
Unsaturated triaxial tests were carried out to study deformation behavior, effective stress path and water retention property of consolidated loam during consolidation and shearing processes. Initial matric suction was set as 0, 50, and 90 kPa, and confining pressures (net normal stresses) were set as 100 kPa. Then shearing processes were done under undrained and drained conditions. We clarified the relation between void ratio and Van Genuchten model parameter by using water retention curve. To predict the unsaturated shearing behavior, a modified Cam Clay model considering void ratio dependent Van Genuchten parameter was proposed. Those numerical test results were agreed well with laboratory tests results.
In order to investigate the effects of overconsolidation and cyclic prestrain history on the relationship between penetration resistance qt and liquefaction strength RL for sands containing fines, miniature cone penetration tests and subsequent cyclic loading tests are carried out in triaxial test specimens. A unique line relating cone resistance and liquefaction strength has been found irrespective of fines content Fc for sands with given overconsolidation stress/prestrain history, indicating that the history tends to increase the liquefaction strength corresponding to a given qt - value. In a comparison with similar results of accelerated tests simulating longtime cementation effect by adding small amount of cements to fines, it is clarified that a modification of RL corresponding to Fc in the current liquefaction potential evaluation practice cannot apply to the aging effect by overconsolidation and presstraining histories.
Plastic board drain (PBD) method is a consolidation method which can accelerate consolidation by placing a lot of PBD into the soft ground. It is important for PBD method to get information about the layer thickness of soft ground and geological distribution, before designing the optimal arrangement of PBD. However, it is difficult to get the accurate information by soil exploration with an only few samples. In this paper, the simplified estimating equation is proposed that evaluates cone bearing capacity by using oil pressure resistance of placing PBD machine during operating. Furthermore, the system is proposed that can evaluate the distribution in three dimensions of ground strength by using estimated cone bearing capacity. Finally, it was confirmed that this proposed system could evaluate the layer thickness of soft ground and geological distribution accurately.
Steel pipe piles with wings installed in soil cement column is a composite foundation of pile consisting of soil improvement with cement and steel pipe with wings. This type of pile shows higher vertical bearing capacity when compared to steel pipe piles that are installed without soil cement. It is thought the wings contribute to higher bearing capacity of this type of piles. The wings are also thought to play the role of structural unification of pile foundations and load transfer. In this study, model test and 3D elastic finite element analysis was carried out in order to elucidate the effect of wings on the structural unification of pile foundation and the load transfer mechanism. Firstly, the model test was carried out in order to grasp the influence of pile with and without wings, the shape of wings of the pile and the unconfined compression strength of the soil cement on the structural unification of the pile foundation. The numerical analysis of the model test was then carried out on the intermediate part of the pile foundation with wings and mathematical model developed. Finally load tran sfer mechanism was checked for the entire length of the pile through this mathematical model and the load sharing ratio of the wings and stress distribution occurring in the soil cement clarified. In addition, the effect of the wing interval on the structural unification of the pile foundation and load transfer was also checked and clarified.
In this study, a shaking table test was carried out in order to discuss the dynamic behavior for the bend of pressure pipeline with a concrete block and thrust restraints using geogrids or gravels in liquefying ground. As a result, it was revealed that the concrete block was largely moved and the relative displacement between the bend and the adjacent pipe became large. On the other hand, it was proved that geogrids and gravels were very effective for the lateral resistance in liquefying ground. In addition, the relative displacement was small because of the same difference between the bend and the adjacent pipe.
Recently, in Japan, due to increase of torrential ra infall event with locally-hig h intensity, which may be regarded as one phenomenon of climate change, frequency of subsequent natural slope failure event has drastically been increasing. Therefore, it is an urgent task to clarify mechanism of both surface flow and moisture infiltration into subsoil caused by torrential rainfall, focusing water mass balance in slopes. However, the investigation includes difficulties on data storage on historical rainfall records, and site selection of field monitoring. From such viewpoints, authors had started filed monitoring jointly with Kasetsart Univ., focusing on the similarity of rainfall characteristics between torrential rainfall event with locally-high intensity observed in Japan and squall in tropical countries. In this study, it is discussed to investigate whether or not the findings obtained through field monitoring in Thailand are applicable to torrential rainfall in Japan based on the comparative study of rainfall and geological characteristics in the two co untries. In addition, as well as the introduction of the current research works on early warning system considering the effect of antecedent rainfall on slope failure installed in Thailand, the feasibility of the system to be installed in Japan is discussed.