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

Mibaidai landslide is a huge ancient landslide in Xinping county of Yunnan province, about 6km away from Laochang town. Laochang town's bamboo garden villages Mibaidai, Sanhongdai and Gebu village are located in it.This thesis, taking Mibaidai landslide as the research object, based on the site geological survey, geological materials collection, and analysis, illustrated in detail the engineering geological characteristics of Mibaidai landslide, and generalized geomechanics model of the landslide's formation according to it; through rock sampling, lab tests and engineering geological analogy method, it gained the main physical and mechanical parameters of this landslide's rock body; through the counter-succession analysis of the landslide body, it analyzed slope's stability under natural condition by limit equilibrium theory; and it computed and analyzed the slope's stability under earthquake action by pseudo-static method when using the inertial force system to simplify earthquake action. Finally the thesis made simulation analysis for the slope's deformation evolution by FLAC^2D numerical analysis software.According to the research, it is thought that the rock body of Mibaidai slope's origin zone is dolomite quartz leptynite, which has mica schist weak intercalation in the shape of thin flakes in it. The sliding body's material composition has the three-layer structural characteristics of hard upper layer, soft middle layer and hard lower layer in macroscopic view, the overlying and underlying relatively hard layer is dolomite quartz leptynite, and the middle weak intercalation is dolomite schist. The rock body schistosity plane is nearly horizontal and has developed a set of joints outward to the slope, orthogonal with the schistosity plane. Under tectonic movement and unloading effect, it's very easy to develop tension cracking on the top of the slope along the steep joints developed in rock body, this special material composition and structural plane combination form resulted in the through plane on the top of the slope along this structural plane, which made the slope easy to creep downward along the tension crack and dolomite schist weak intercalation. Mibaidai landslide sliding origin zone is weak base slope, its side slope with the geomechanics model characteristics of deep plastic flow-tension crack. The slope body developed by landslide took place progressive failure caused by the above special material composition, rock mass physical mechanical property as well as the control of structural plane under gravity, finally the slope lost stability and landslide happened under the earthquake action.In the aspects of stability computation, this thesis first adopted the limit equilibrium theory analysis and pseudo-static method to make computation and analysis for the slope's stability. The computation result shows that when not considering the earthquake action, the slope is stable, while when considering the earthquake action, the slope loses stability.The result of numerical analysis shows that when the slope is under natural condition, the lower base of slope and the middle and lower place of the overlying rocks of weak formation appears shear stress concentration, formation of shear yield region along the weak intercalation as well as relatively small displacement and the slope is stable; while under the triggering action of earthquake, the slope body's shear stress and displacement leaps, the slope's trailing edge joint's opening increases gradually, the yield region gradually expands through and the slope lost stability.