The Geometric Characteristics and Initiation Mechanisms of the Earthquake- Triggered Daguangbao Landslide

Thursday, 18 December 2014
Jia-Jyun Dong1, C. C. Tsao1, Che-Ming Yang1, Wen-Jie Wu1, Chyi-Tyi Lee1, M. L. Lin2, W. F. Zhang3, X. J. Pei3, G. H. Wang4 and Runqiu Huang3, (1)NCU National Central University of Taiwan, Jhongli, Taiwan, (2)National Taiwan University, Taipei, Taiwan, (3)Chengdu University of Technology, China, The State Key Laboratory of Geohazards Prevention and Geoenvironment Protection, Chengdu, Sichuan,, China, (4)Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Japan
Recently, catastrophic landslides are getting considerable attentions not only from natural hazard but also from geo-material science. In the past century, the Daguangbao (DGB) landslide which triggered by the Wenchuan earthquake is one of the largest earthquake- triggered landslides. Our main goal is to characterize the geometry of DGB landslide to better determine the initiation mechanisms. Based on the remote sensing images analysis and field investigation, we proposed an atypical wedge model of DGB landslide compose of a folded strata and a zigzag stepping-out joint system, which outcropped at the south and north of the landslide site, respectively. The intersection line of wedge is curved, counterclockwise rotated and daylighted, which fit the pre- and post- position of the mining tent with 1.9 km displacements. The volume of sliding mass was evaluated to 10.51×108 m3 by the atypical wedge model. The identified slip zone of DGB landslide consists of the breccia and gouge layers in the dolomite strata. The rotary-shear tests were performed with the intact dolomite rocks near the slip zone and the gouges in the slip zone to determine the strength of slip surface. The peak and the steady-state friction coefficient of the tested dry dolomite discontinuities, wet gouges are 0.52~0.96, 0.73~0.86 and 0.1~0.57, 0.16~0.63, respectively. Although the result of static wedge stability analysis shows that the slope is quite stable (F.S. = 4), but the result of pseudo-static wedge stability analysis with seismic coefficient will trigger the gigantic wedge by the Wenchuan earthquake. Moreover, the friction coefficient of the tested gouges after long slip displacements as shear velocity exceeds 1.3 m/s will lower than 0.25 (=tan(14°); the intersection line plunged 14°). Therefore, the gigantic wedge can be accelerated by the inertial force and keep moving rapidly with long run-out. According to the calculations of simple one dimensional particle motion model, DGB landslide traveled 52~68 seconds with a maximum velocity of 58~75 m/sec.