Kensuke KAWASHIMA

Shear strength property of landslide slope due to sliding history and failure prediction of landslide with inversion of stiffness factor from field observation

Satoru OHTSUKA

Landslide takes place due to rainfall and/or melted snow, where the groundwater level rises and the shear strength decreases. In this study, the ring shear test was carried out to investigate the shear strength for the change in pore water pressure at the first occurred landslide and the repetitive landslide. From the tests, the followings were concluded.
1.The testing soils were the Okimi and the Kaolin clays. From the test results, the yield point was located on the critical state line. On the contrary, the failure point changed due to the over consolidation ratio and as the value of the over consolidation ratio bigger, the more the specimen could hold on to the pore water pressure loadings.
2.In vertical stress decreasing test on a specimen of residual state, there was no deformation observed till the yield point and the specimen was denoted brittle. Thus, the failure and the yield points showed almost the same.
3.Angle of shear resistance decreased greatly due to pre-shearing arriving at the residual state. The yield and the failure points were obtained as a parallel line to the critical state line exerted by the angle of shear resistance at residual state.

In this study, other than the mechanical test on clay along the slip line, due to the triaxial test, the inverse analysis of the behaviour of the specimen on the pore water pressure loading test was carried out as the new method of landslide prediction. The pore water pressure loading test was taken as a landslide model test to show the same time dependency behaviour as creep. From these behaviours, the stiffness factor regarding the effective stress was rationally defined. The conclusions are as below.
1.Stiffness factor regarding the effective stress expressed the total stiffness of specimen in pore water pressure properly. The change for pore water pressure afforded the failure prediction properly.
2.Accuracy of inversed stiffness factor depended on the magnitude of displacement. It got precisely after passing the yield point since the displacement increased.
3.Realtime inversed stiffness factor was shown to be applicable to failure prediction of landslide.