Failure mode analysis of post-seismic rockfall in shattered mountains exemplified by detailed investigation and numerica
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Kun He I Yongjian Li I Guotao Ma I Xiewen Hu I Bo Liu I Zhigang Ma I Zepeng Xu
Failure mode analysis of post-seismic rockfall in shattered mountains exemplified by detailed investigation and numerical modelling
Abstract A high-position destructive rockfall, significantly influenced by post-seismic effect of Wenchuan earthquake in 2008 and associated aftershocks, was reported in Miansi Town of Wenchuan County, Sichuan Province, China. About 3,000 m3 of rock at high position detached from a dipping rocky slope, which manifested as a translational motion. Detailed field investigation, geological mapping, kinematic analysis, and numerical modelling are presented to comprehensively analyze the complex failure mode of the post-seismic rockfall. The results demonstrated that the sliding surfaces are mainly controlled by the internal shear discontinuity sets. The backscarps are progressively evolved from the tensile cracks at rear slopes caused by the Wenchuan earthquake. Because of the combination effect of heavily shocks of previous earthquake and local geomorphology of the rockfall with beneficial for facilitating the magnification effect on peak ground acceleration (PGA), the rock mass of slopes is dramatically damaged and fractured. The original intact slopes finally developed to the shattered slopes as an optimum birthplace for the post-seismic rockfalls. It should be noticed that intensive precipitation plays a triggering factor that generates the hydrostatic water pressure in the rear cracks and the uplift pressure at the bottom sliding surface within a short time. The evolution processes are divided into three stages: slope relaxation stage, rock shattering and disaggregation stage, and high-speed falling stage. Velocities, energy, and bounce heights of falling rock blocks are computed by the RocPro3D software for understanding the corresponding kinematics. The paper can provide an insight into post-seismic rockfalls in the tectonic areas associated with the combination of seismic activities and intense rainfall. Keywords Shattered mountain . Structural control . Geomorphological control . Rainfall . Miansi postseismic rockfallYongjian Li and Guotao Ma as co-authors contributed equally to this work. Introduction Rockfalls or rock slope failures are one of the most common geological disasters which are characterized by high mobility and catastrophic impact energy (Whalley 1984; Wieczorek et al. 1998; Guzzetti et al. 2002; Ferrari et al. 2013; Hungr et al. 2014). The common triggering mechanisms of rockfalls mainly involve large-scale tectonic activity, heavy precipitation, and anthropologic disturbance. Ground movement in seismic areas as well as the failure of rock slopes associated with strong shaking has been studied by a large amount of researchers (Wasowski et al. 2011; Chen et al. 2012). According to literature, many studies concentrated on mechanisms, distribution characteristics, and development of rock slope failures induced by earthquakes (Wang and Sassa 2009; Yin et al. 2009; Jibson 2011; Xu et al. 2017
