Evaluation of the shear strength on undisturbed slip surface by newly developed Slip Surface Direct Shear (SSDS) apparatus

This paper describes both the principles of Slip Surface Direct Shear apparatus (SSDS) that would be able to adjust the position of slip surface to coincide with the shear surface of the apparatus and the results of the test in use of it. The number of tested slip surfaces is124. These were taken from Tertiary strata landslides, shear zone landslides and solfataric landslides. From the test results, a typical stress path on the slip surface is recognized. The results obtained from Tertiary strata landslides clearly show that the residual shear strength is affected by slip surface covered with thin smectitic clay. As for the shear zone landslides, test results show that the residual shear strength is strongly affected by the coarse size grain content in the slip surface clay. Comparing SSDS data with that of ring shear tests, authors have found that if the sample prepared for a ring shear test has the same clay content as the slip surface clay, both results show the same strength parameter.