<学術報告>地すべり土の残留強度と残留状態からの強度の回復に関する研究

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The reactivated landslide has been subjected to repeated sliding and recession since the geological age. The shear strength of the shear zone is reduced to the residual state during sliding, but could be recovered to some extent during the recession period. This study describes the residual strength characteristics and the strength recovery from the residual state by means of a ring-shear test, for landslide soils which showed a considerable variation in physical and mineralogical composition. 1. The appropriate relation was obtained in the whole range between the residual strength parameter φ, and the total of the contents of preferred-oriented clay minerals (smectite, vermiculite, chlorite mica) in the <420μm soil samples. The relationship between them was expressed as a chair-shaped curve and the transitional region in which control of φ, changed from the non-preferred-oriented minerals to the preferred-oriented clay minerals was clearly observed. It is indicated that the parameter of φ, could be estimated based on the relationship φ, and the total contents of preferred-oriented clay minerals in the <420 μm soil samples. 2. Based on the relationship between the residual friction coefficient and effective normal stress, the curvilineared residual strength envelope was divided into tow parts which are the lower half and the higher half of hte effective normal stress. The residual strength parameters were determined at each part, cr was not zero at the lower half of the effective normal stress while it was zero at the higher half, and φ, was greater at the lower half than that at the higher half. 3. The recovery of the shear strength of the samples contained high amount of sand particlessubjected to large-displacement sheaar by re-consolidation was clearly detected at the effective normal stresses below 150kPa. The recovery rate increased with the decreasing normal stress but the strength did not recover to the level of the fully-softened stregth. Furthermore, for the samples contained high amount of clay particles, the rate of decrease in the strength against the peak strength was gerat but the recovery rate was negligible at the whole normal stress. The differences between the recovered strength and the residual strength were 1°-4° for the samples contained high amount of sand. 4. Landslide soils containing high amount of silt and sand and dominating with quartz and feldspars showed a strong recovery of strength at effective normal stresses until 400kPa, due to the re-consolidation effect on the disturved thin-layer still existing on the shear surface in the residual state. In landslide soils dominating with quartz and feldspars but containin gconsiderable amounts of mica and chlorite, the recovery of strength was noticed at lower normal stresses but hardly seen at higher normal stresses. This is ascribable to the formation of residual shear surface due to the presence of preferred-oriented minerals at higher normal stresses. The recovery of strength was not essentially recognized in landslide soils dominated by prefered-oriented minerals such as smectite, due to the development of residual shear surface to make slickenside.
琉球大学の論文
2002-12-01

<学術報告>地すべり土の残留強度と残留状態からの強度の回復に関する研究

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