| Co-Investigator(Kenkyū-buntansha) |
YOKOTA Kinutada Ehime University, Faculty of Engineering, Assoc. Professor, 工学部, 助教授 (30036363)
YAGI Norio Ehime University, Faculty of Engineering, Professor, 工学部, 教授 (00027228)
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| Research Abstract |
Residual state of a soil in shear deformation is a state when change in soil volume during the shear is zero, and it is attained when all the soil particles on the shear planes get reoriented toward the shear direction. Residual state of soil plays a significant role in landslide stability problems because strength of slip surface soil is governed by the residual conditions after having slid for a long duration. It is therefore important to investigate the strength behaviors of landslide soils at their residual states and to employ them in the stability analysis. This research includes two major lab investigations: 1) strength properties of landslide soils and 2) influence of clay minerals on soil strength. The investigation results were then employed in carrying out stability analysis of the landslides. Several soil samples were obtained from various landslide sites in Shikoku representing various geological conditions for the lab tests. The strength properties were investigated by ri
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ng shear apparatuses based on direct as well as simple shear principles, and the mineral properties were investigated by x-ray diffraction analysis. The investigation results are summarized as follows.
First, the strength measured by direct shear type ring shear apparatus was found to differ in many aspects from that by the simple shear type. It is because the direct shear type apparatus possesses a pre-specified plane of shear, which may result in a lower residual strength of a soil with higher content of finer particles and a higher strength of a soil with higher percentage of coarser particles. In contrast, a simple shear type apparatus gives comparatively accurate results because the soil sample gets sheared though the weakest plane in the entire depth of specimen. Second, the shear strength of landslide soils in Shikoku was investigated to be very low, which is mainly due to a significant amount of expansive clay minerals in the slip surface soil. The x-ray diffraction tests revealed that the amount of expansive chlorite in landslide soils originated from metamorphic rocks in particular is high, which plays a significant role in lowering the soil strength. Third, the stability analyses results showed that the slip surface soils, especially in case of large-scale landslides have reached the residual state, which was confirmed by back analysis of some active landslides. Finally, it was considered that application of lab-determined strength parameters in stability analysis for the landslides is more feasible in many aspects than carrying out back analysis. Less
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