Sliding-Surface Liquefaction and Undrained Steady-State Shear-Strength

AbstractThe sliding-surface liquefaction (SSL) is one of the most important concepts to understand and reduce rapid landslide disaster risk. SSL occurs even in dense sandy layers. SSL is caused by a series of phenomena, 1) grain-crushing due to shearing under overburden pressure in the shear zone, 2) volume reduction in the shear zone, 3) generation of high pore-water pressure in the shear zone, and 4) liquefaction of the shear zone material.After SSL, a mass of soil layer above the liquified sliding surface moves at high speed. Motion of sandy layer above the liquified sliding-surface was physically simulated under the corresponding normal stress by the undrained stress-control ring-shear apparatus. The shear stress acting on the sliding-surface and the generated pore pressure near the sliding surface are monitored. After failure, shear strength mobilized on the shear zone decreases by the effects of increased pore-water pressure, then, the shear strength working on the shear surface together with the generated pore pressure reaches a certain constant value which is the undrained steady-state shear-strength (USS). After reaching to USS, only shear displacement is increased without any change of shear stress and pore pressure. It is a common feature of rapid and long-travelling landslides which poses a high risk to people living in/near slopes.