Study On Engineering Geology Characteristics And Causing Mechanism Of Bajiaoshu Landslide In Xinping, Yunan

Bajiaoshu landslide, which happened at 8:30, on 14^th of August, 2002, was located in Xinping, Yunnan Province. The lanslide destroyed the Village of Bajiaoshu, with 8 died and 3 lost.In this paper, Bajiaoshu landslide was studied. Based on in-situ geological survey and the analysis of geological data, engineering geology characteristics of landslide were expatiated particularly, and geo-mechanical model of landslide was proposed. Physical parameters of main rocks were obtained by rock tests and geological analogism. The impact on slope stability of under ground water was analysed by limit equilibrium method. And the starting velocity under water-cushion influence and maximal sliding velocity were gained by Energy Conservation Theory. Properties of stress, displacement and the extension of failed regions of the slope both under natural state and in rainstorm stage, were calculated by FLAC in this paper.The primal slope of Bajiaoshu landslide, which was consequent slpoe, was composed of biotite-plagioclase gneiss, while papery dolomite schist existed as a piece of interlayer. The composition of slope was provided with the three-ply property of up hard-mid soft-down hard as a pieceof hamburger. The up hard rock mass could easily slip creeply along the soft layer, which led crack occuring in the upside of slope. The deformation of slope was restrained by former hard rock mass, which acted as a locked segment, because the soft layer didn't contact the air. So a geo-mechanical model of upside fracturing-mid sliding-under lucking-up was introduced to Bajiaoshu landslide in this paper. The landslide was controlled not only by special composition of material, but also mechanical characteristics and interfaces of rock mass. Under the action of gravity, the slope deteriorated gradually. Rainstorm generated high pore water pressure in back-crack and soft layer, which triggered the landslide.The results of limit equilibrium method showed that the slope was stable without consideration of the action of under ground water, but the slope failed while taking the influence of under ground water into account. The velocity at the time of sliding mass shearing out and the maximal velocity were obtained by Energy Conservation Theory. They were 39.8 m/s and 44.5 m/s, respectively. The results of numerical simulation showed that slope was stable under natural state, but in rainstorm stage, yielded regions in slope extended because of quick increasement of shear stress and displacement of slope. Once yielded regions ran through, the solpe failed.