301. The Normal Stress on the Slip Surface: A Dominating Factor on the Run-Out Distance of the Sliding Rock Mass

The excessive travel distances have been observed for the landslides with abnormal large volume. The dominating mechanisms are still controversial. It is evidence that the volume of landslide is highly related to the thickness of the sliding mass. Accordingly, it is reasonable to speculate that the normal stress on the sliding surface could dominate the kinematics of landslides. This study tries to testify this conjecture experimentally. Series of rotary shear tests of dry sandstones and wet gouges under different normal stress are performed with an equivalent slip rate of 1.3 m/s. Interestingly, the steady-state friction coefficients of the tested samples, which is highly related to the kinematics of landslides, are decreased with increasing normal stress. The steady-state friction coefficients of the tested sandstones will decrease from 0.69 to 0.35 when the applied normal stresses were increased from 0.5 to 3.0 MPa. Moreover, the steady-state friction coefficients of the tested wet gouges will decrease from 0.26 to an extremely low value of 0.04. Simplified rigid block model predicted the travel distance increased with increasing normal stress. A normal stress threshold of 1.5 MPa on the sliding surface of the dry sandstone was observed to induce excessive travel distance. On the other hand, even with a low normal stress of 0.5 MPa, the sliding surface composed of wet gouges experienced large excessive travel distance. The results revealed that the normal stress on the sliding surface, as well as the sheared materials and their water content, of the large landslides dominating travel distance.