Experimental Simulation of Landslide Creep in Ring Shear Machine

Abstract Soil material undergoes a volumetric change when deformed, and the change continues until the material reaches its critical state. In granular soils, the critical state is one that exhibits the least frictional resistance, but in clayey materials, the frictional resistance decreases further upon shearing due to particle reorientation in the plane of failure, and the material volume attains a stable or steady state only after a large amount of shear deformation, which depending on the material type varies from a few to tens of centimeters. This state of shear deformation is generally known as the residual state. This article focuses on residual-state creep shear tests on common clayey materials for the purpose of experimentally simulating the landslide creep and understanding the displacement behavior of large-scale creeping landslides. As a general understanding, the deep-seated creeping landslides displace as a result of residual-state shearing of clayey material in the slip surface. So, a modified bishop-type torsional ring shear machine was developed for studying the residual-state shear creep behavior of clayey soils. In the ring shear tests, the material is first sheared under a strain-controlled pattern, and after the sample reaches its residual state of shear, different sets of constant shear loads are applied until the sample fails again and again. The test results reveal that at the residual state of shear, the creep behavior is exhibited only after a load equivalent to the residual frictional resistance of the material is applied. Moreover, it was understood that the displacement required for the beginning of the tertiary stage of creep of particular soil material, i.e., the early stage of creep failure is the same for all sets of creep loads.