Influence of Topographic and Rainfall Conditions to Shear Deformation of Steep Sandy Slope

Abstract

In order to examine the utility of slope surface displacement measurement for the investigation of slope instability, effect of slope angle, soil layer depth, rainfall intensity, and initial suction in the slope to the proceeding of shear deformation of the slope and surface displacement were examined by the numerical simulation. The simulation used the shear deformation model of infinite slope due to rainfall, which had been already proposed by the author. As results, following facts were made clear.(1) With the increase of slope angle, rainfall intensity and decrease of soil layer depth, initial suction, remaining time until slope collapse becomes shorter. The increase of remaining time until slope collapse is proportional to the increase of soil layer depth, but the rate of decrease of the remaining time becomes larger in accompany with the increase of slope angle, rainfall intensity and the decrease of initial suction.(2) Local shear deformation in the slope develops largely in the high water content layer near the bottom which is formed by the arrival of the vertical unsaturated seepage water, although local deformation at the upper part with small water content is very small. The local deformation around the bottom becomes larger in accompany with slope angle and soil layer depth. In the case of large soil layer depth, shear deformation develops at every depth without high water content at each depth.(3) With the increase of slope angle and soil layer depth, surface displacement grows relatively large at early stage of displacement so that detecting slope instability in early stage can be easier. On the other hand, change of rainfall intensity doesn't affect to the shape of surface displacement curve. On the initial suction of the slope, surface displacement can grow large at early stage in the case with very low suction condition (wet condition), while initial suction doesn't affect to the shape of the surface displacement curve in a case of relatively high suction condition (dry condition).