The Research Of Weathered Layer Slope's Progressive Failure Of Low-grade Metamorphic Rock

Along with the rapid development of our society and economy, our construction activities become more intensive. The velocity of Chinese highway construction has become faster and faster since the policy of reform and opening up. As a relatively poor southwest province, the road under construction in Guizhou has grew exponentially in recent years. During the construction, various problems and difficulties are encountered because of the diversiform landform and complex geological.Against so many unstable epimetamorphic rock slopes during the highway construction of SanSui to KaiLi in Guizhou province, the Nanyuegou landslide which located at the 13th contract K126+700-K127+300 of this highway was selected as example for analysis. The topography, geomorphology, hydrogeology, rock composition and their mechanic parameters of Nanyuegou landslide were obtained by pre-site survey, and some of the slope's deformation and sliding trend were gathered through on-site inspection before the governance.Based on the situation of Nanyuegou landslide, the slope stability analysis was carried out by the application of FEM strength reduction method, obtaining the plastic zone distribution area of the slope. Combined with the on-site monitoring data, a reasonable sliding surface position can be determined. Then disperse the sliding body above the sliding surface and add the spring units to all nodes of sliding surface through a self modeling program, simulating the sliding bottom friction between the sliding body and the sliding bed. The development of progressive failure of slope and force conditions of slip surface has been studied, the conclusions are as follows:(1) Epimetamorphic rock may gradually develop to sliding surface, because of broken rock, poor integrity, rock mechanics parameters will significantly reduced by weathering, easily been weak layer forms after weathering, it may make the whole slope instability under the influence of external factors, such as strong rainfall, excavation engineering and so on.(2) According to the Nanyuegou landslide simulation of gradual destruction process, the instability of these slopes is caused by free face of the posterior edge because of the excavation of the front edge or the crack formed by slip resistance section reduction of the front edge, the posterior edge creeps down step by step, leading to the landslide of the slip mass and the integral instability of slope。(3) By the analysis the plastic zone distribution of four typical sections in Nanyuegou slope, the plastic zone of main sliding surface is biggest, and the speed of plastic zone's expansion in this section is the maximum. With the crack distribution and size of the slope by the on-site inspection, it can be learned that the middle of the slope first to slide, the other section moving with this sliding process, which formed the existing landslide.(4) According the force in sliding slope surface and the trend of the slope safety coefficient in the process of iterative calculation, combined with the on-site inspection results, the failure mode of Nanyuegou slope is slippage (creep)-tensile crack.