Research On Evolution Process And Controlling Mechanism Of Weak Layer From Thick Layered Bedrock Landslide

Layered bedrock slope is the rock-slope with a group of advantage structural surface. In general, the advantage structural surface is rock stratum, weak layer, or joint surface, which is one of the typical features of complex rock mass. It is widely distributed in Southwestern China which is known as mountainous area including Sichuan, Yunnan, Guizhou, Chongqing, Hubei, Hunan, et al. Several weak layers lithology of mudstone, clay rock, or shale, which is developed in layered rock mass of these mountain areas, and the karst zone, and the joint surface, construct the parting plane between rock mass and mountain. The layered rock mass lose stability through long-term creep deformation. In the continuing action, induced disasters such as collapse and landslide,which is usually huge,extremely harmful.This paper takes Jiweishan Landslide as example to research on evolution process and controlling Mechanism of weak layer from thick layered bedrock landslide. On the basis of detailed field geological investigation, find out the geological environment background of landslide causes, the basic characteristics of the landslide and failure history, the failure mode and causes mechanism of landslide. According to the key factors- weak layer and karst zone strength reduction that led to landslide creep failure, combining with the field geological survey and rock analysis test, discussed the sedimentary environment and material basis, the evolution characteristics, rock structure and put forward the evolution mode of weak layer sliding zone of Jiweishan :original weak rock â†' interlayer shear zone â†' sliding zone, and explained the evolution mechanism of weak layer from mineralogy, mechanics and physical chemistry. The rheological mechanics test was carried out to build the nonlinear damage rheological models for different stage of evolution of the weak layer. The finite difference method FLAC3 D is adopted to simulate the shear failure characteristics of karst development with different level. The three-dimensional limit equilibrium analysis mechanics model of layered bedrock landslide controlled by weak layer was built based on the mechanism of the key block theory. Based on the model, calculated the change trend of the slide mass thrust and safety factor, and revealed failure mechanism of layered bedrock landslide controlled by weak layer from the mechanics. The three-dimensional limit equilibrium analysis mechanics model was applied to layered bedrock landslide stability analysis under variable dips condition. The influence law of landslide stability under different schemes and variable dips was obtained. Several results and conclusions form research as follows:(1)The layered bedrock slope failure is affected by topography stratigraphy, geological structure, karst and so on. It has mechanism of blocks in the rear driving and the key block in the front resisting. Landslide failure with the long history, the decreased strength of bottom weak layer, and side boundary karst development zone sheared, make up the key factor of layered bedrock landslide creep failure.(2)The paper analyzed the developmental characters, mineral composition and microstructure during the layered bedrock weak layer. Then, put forward the evolution model of weak layer about Jiweishan landslide. It divided into three stages: original weak rock â†' interlayer shear zone â†' sliding zone, and revealed the evolution mechanism of weak layer from many subjects such as mineralogy, mechanics and physical chemistry.(3)The paper carried out the shear rheological mechanics test. The weak layer mechanical strength parameters of each evolution stage have been obtained through the test. Further, explained the strength parameters attenuation in the evolution, through the rheological characteristic research. By introducing damage variable, built the nonlinear damage rheological models suitable for each stage of evolution of the weak layer. Meanwhile, quantitatively evaluated karst rock mass strength attenuation process.(4)The paper respectively discussed different scheme combinations under boundary strength based on key block theory of Jiweishan landslide. Also, built three-dimensional limit equilibrium analysis mechanics model of layered bedrock landslide controlled by weak layer, and deduced the three dimensions changing tendency of landslide stability under several schemes, further carried on the contrast analysis. Revealed failure mechanism of layered bedrock landslide controlled by weak layer from the mechanics.(5)The paper applied the three-dimensional limit equilibrium analysis to layered landslide stability under variable dips condition,discussed the range of bottom sliding surface and the karst zone shear strength parameters when the landslide is in a critical state. Established the three-dimensional critical surface of landslide under variable dips.