Study On Starting Mechanism Of Dazhai Village High-Speed Landslide In Guanling County Of Guizhou Province

In June28,2010, Dazhai village high-speed landslide disaster, which occurred inGuanling county of Guizhou province, is a rare long-distance high-speed landslidedebris flow in the history of Guizhou province, resulting in a serious consequence of99deaths. Summarizing and analysing the previous study datas of Dazhai high-speedlandslide, it is found that existing research has different defects inordinately, andinitiation mechanism about landslide is not complete.The thesis is supported by the science research item, landslide formationmechanism research of Guizhou province, which is the second topic of GuizhouProvince geological disaster monitoring and early warning and decision supportplatform. At the base of deepening the study of engineering geological conditions,through the analysis of landslide area of the site investigation and research in relateddata, the conceptual model of high-speed landslide formation mechanism is established.The rock and soil physical and mechanical parameters for numerical simulation isobtained, through some conventional soil and rock physical mechanics test onmechanical properties of slope rock mass. The initial stress field and the storm triggerednumerical simulation carried out, according to the obtained physical mechanicsparameters. The initial mechanism of high-speed landslide is analysed in the end. Themain research contents and results are as follows:(1) By analysing the regional geological background, the landslide area landform,formation lithology and rock group, geological structure, weathering and unloading,hydrogeology, neotectonic movement and seismic features, deepening understand thehigh-speed landslide geological conditions, the geological prototype is established. It isconcluded that the topography of slope and hard-soft slope structure are the controlfactors of the landslide, and heavy rainfall is the triggering factors of landslide. (2) Through the process, deformation characteristics investigation of landslide,and combination of geophysical exploration and drilling data, the qualitative analysis ofthe formation mechanism of landslide is carried out and compression–dumpinginstability mode is obtained.(3) Using three-dimensional finite element analysis, it is revealed that the processof stress, deformation evolution and characteristics of Dazhai slope. The results showthat there are a certain of cracks in the slope trailing edge in the process of the slopeformation, the potential shear surface has been basically formed in the depth of20-30mbelow the slope surface, the underlying Longtan Formation boundaries has formed alocking section of rock mass.(4) Using two-dimensional finite element analysis, instantaneous effect of237mmrainfall to the landslide15h before sliding is calculated. The results show that theinstantaneous rainfall caused instability slope potential shear surface forming slidingsurface, the locking section of rock mass moves toward the free surface0.04m.(5) The qualitative analysis about the high-speed landslide and startup mechanismshows that, the soft underlying Longtan group constantly compression-deformationpromote the tensile cracks developing to the deep in the trailing edge and gradually andforms potential shear surface with shear strain concentration, increasing the shear stressto the locking section of rock mass. At this point, deformation and destructioncontinues along the potential shear,and the slope is in stable broken. From June27th toJune28th, the continuous rainfall, especially the15h strong rainfall before breaking, alot of water has been injected into slope along the early crack. And powerful hydrostaticpressure along the early potential shear surface pushes the slope toward the free surface.The top-down seepage water forms dynamic water pressure. The saturated rock mass ofslope led to its mechanical properties change, the value of C,φ decreasing. Under thealliance of three actions above, the stable broken of slope ends, the locking segment ofrock mass at the toe is nipped, high speed landslide occurred with sudden brittle failure.