Abstract
A new consolidated undrained ring shear test capable of measuring the pore pressures is presented to investigate the initiation mechanism of the Hsien-du-shan rock avalanche, triggered by Typhoon Morakot, in southern Taiwan. The postpeak state of the landslide surface between the Tangenshan sandstone and the remolded landslide gouge is discussed to address the unstable geomorphological precursors observed before the landslide occurred. Experimental results show that the internal friction angle of the high water content sliding surface in the total stress state, between 25.3 and 26.1°, clarifies the reason of the stable slope prior to Typhoon Morakot. In addition, during the ring shear tests, it is observed that the excess pore pressure is generated by the shear contractions of the sliding surface. The remolded landslide gouge, sheared under the high normal stress, rendered results associated with high shear strength, small shear contraction, low hydraulic conductivity, and continuous excess pore pressure. The excess pore pressure feedback at the sliding surface may have accelerated the landslide.
Highlights
In 2009, the Hsien-du-shan landslide, triggered by Typhoon Morakot [1, 2], killed more than 400 people at the Hsiaolin village, Kaohsiung, Taiwan
consolidated undrained (CU) ring shear tests were conducted on the interface of the Tangenshan sandstone and the remolded landslide gouges to clarify the mechanical behavior of this surface under large shear displacement
The capacity of the new device is ascertained by the successful modelling of the initiation of the heavy rainfall-induced Hsien-du-shan rock avalanche at the sandstone/landslide gouge interface with a maximum normal stress exceeding 2 MPa
Summary
In 2009, the Hsien-du-shan landslide, triggered by Typhoon Morakot [1, 2], killed more than 400 people at the Hsiaolin village, Kaohsiung, Taiwan. Before this landslide mobilized, the authority announced two potential debris flow torrents (Kaohsiung County DF06 and DF07) (http://246.swcb.gov .tw/allfiles/PDF/98%E5%B9%B4%E8%8E%AB%E6%8B%89 %E5%85%8B%E9%A2%B1%E9%A2%A8-%E9%AB%98%E 9%9B%84%E7%94%B2%E4%BB%99-001-(%E9%80%9F).pdf) as major threats to the local residents in the Hsiaolin village. Lee and Delaney [9] concluded analytically that the rise in temperature and pore pressure were, respectively, 200 K and 0.2–2 MPa during the movement of the San Andreas Fault zone with an average stress of 10 MPa
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