An experimental study to characterize the initiation of the seismic-induced Tsaoling rock avalanche

The Tsaoling rock avalanche, which had a sliding volume of 120 million m3 and a maximum thickness of 170 m, was triggered by the Chi-Chi earthquake in 1999. However, the initiation mechanism has not been well understood because different friction models have been proposed to describe the triggering process using the Newmark sliding model and numerical simulations. In this study, a new dynamic ring-shear test with a maximum normal stress higher than 3400 kPa is applied as an alternative approach to investigate the initiation of the seismic-induced rock avalanche along the wet sliding surface at the interface of the Cholan sandstone and consolidated remold shale. Experimental results verify that the seismic stresses at the wet sliding surface touch the failure surface and generate significant cumulative shear displacements. Additionally, the shear surface should have non-linear failure criteria rather than the well-known linear Mohr-Coulomb failure criteria with a constant friction angle. Furthermore, the initiation time of the Tsaoling rock avalanche obtained from the dynamic ring-shear test is strongly correlated with the available seismic signal interpretations and the interviews of witnesses who travelled with the sliding mass. This is the first experiment clarifying the co-seismic behavior of the sliding surface and the initiation of the Tsaoling landslide during the Chi-Chi earthquake. Additionally, from the development of the ring-shear test, the integrations of high normal stress, the wet sandstone/shale interface, and the dynamic test with seismic loadings greatly extend the use of ring-shear tests to rock avalanches.