| According to the relevant documents and previous data of typical landslides with interbedded soft and hard rock beddings of low dip angles, this kind of landslide mainly distributes in area of Red beds in eastern Sichuan and Tongren in Guizhou. The characteristics of this kind of landslide are characterized by the difficulty to identify, strong concealment, complicated mechanism of formation, a number of controversies, unique model of failure, great difficulty to hazard prevention and reduction and high risk. Combined with the subject of my tutor –“study on characteristics of geological structure and hazard-formation model of large-scale landslide in the western mountain area”--which belongs to 973 scientific research projects named “study on geological mechanic behavior and hazard-formation during long-term evolution of large-scale landslide”, taking KuaLiangzi landslide and XiangShuping landslide as examples, based on data of investigation and collection in situ and the deep understanding of geological conditions of engineering, the characteristics of deformation and failure and main influence factors of Kua Liangzi landslide and XiangShuping landslide have been analyzed in detail, and conceptual model of deformation and failure of this kind of landslide was established. Based on the test of rock physical mechanical properties, utilizing physical simulation method and numerical analysis method, mechanism of deformation and failure of landslide with soft and hard interbedded structure with low dip angle have been further analyzed, which contributes to further forecast when and where landslide will happen, so that it has enough time to prevent landslide from happening and can reduce the loss of life and property.The main achievements of this paper are as follow:1. Landslide with interbedded soft and hard rock beddings of low dip angles mainly occurred in certain slope, of which dip is range from 3°to12°, the upper of lithologic association is hard and the lower is soft, whole gradient characterized by steep on gentle less than 20°, rock bedding characterized by interbedded soft and hard structure, the thickness of soft rock is generally 2m to 25 m and the hard rock is generally 5m to 30 m. Hard rock stratum developing steep joints. The angle between the active slide direction and dip is generally varied from 0°to 5°. Geometric size of the slope body is characterized by 360 m to1200m in length, 210 m to 2100 m in width, and 15 m to 46 m in thickness. According to the valley incision depth, the landslide with interbedded soft and hard rock beddings of low dip angles can be divided into two types, namely, light-incision landslide and deep-incision landslide.2. Based on similar theorem, and combined with principle of framed physical simulation test, the similarity relation of test model formation mechanism of Kualiangzi landslide is established. Filling fissure in the of the slope to simulated heavy rainfall, which causes the fissures in back of the slope are filling with water and the water tables are rising. According to the growth of water tables and the deformation failure phenomenon of the model, the deformation failure characteristics of slope and the distribution characteristics of groundwater pressure with heavy rainfall are studied. The main results of the research are:(1) Based on characteristics of deformation and failure of the model, the deformation and failure process of Kualiangzi landslide under the condition of heavy rainfall is divided into three stages, namely, the stage of uplift in the middle of slope, the stage of sliding and fracturing in the head of slope, and the stage of sliding-fracturing tendency formation over the whole slope.(2) Experimental results show that under conditions of slope surface being fully covered with lower permeable layer, confined water head height of slope body increases gradually from the trailing edge to leading edge. Both anti-deformation ability of slope surface and increase rate of confined water head height will decrease with the increase of rock strata dip angle, and the water plugging effect reduced accordingly. The confined water head in slope is proportional to the coverage rate.3. Based on the “geological process mechanisms”, using GeoStudio2007, the two-dimensional numerical simulation software, to establish unified calculation model. Taking KuaLiangzi landslide as example, it traces the formation process of the valley and the progressive deformation failure of the slope with the heavy rainfall to analyze the formation mechanism of this landslide and taking XiangShuping landslide as example, it traces the formation process of the valley and the progressive deformation failure of the slope to analyze the formation mechanism of this landslide.And the numerical simulation analysis acquires results:(1) For the former, it is characterized by small valley incision depth and slope relaxation depth, less unloading cracks and integrity of the slope body. However, fissures in the trailing edge of landslide keep expanding and deep-long fractures come into being because of long-term weathering and unloading and unequal rates of creep damage of soft-hard rock. Eventually, the rock mass begin to gradually soften. At the same times, the landslide was horizontally pushed out in the presence of hydrostatic pressure at trailing edge and uplift pressure at surface of rupture.(2) For the latter, the typical of deep-incision landslide with interbedded soft and hard rock beddings,is characterized by big valley incision depth and slope relaxation depth and great unloading rebound deformation. After continuous weathering and heavy rainfall, there was local devastation in the slope. Gradual failure in the lower part of the slope promotes further relaxation in the upper slope. In addition, the free surface condition is a good prerequisite to make the slope finally fail, which is manifested as progressively retrogressive slippage from the bottom to the top.4. The occurrence of landslide with interbedded soft and hard rock beddings of low dip angles needs several geological factors, namely, geography of heavy eroded short terrain and hill, strata lithology of interbedded soft and hard rock beddings, faint geological structure, favorable water catchment and storage conditions, and free surface conditions. Valley incision is the motivating factor, and heavy rainfall the inducing factor.5. To light-incision Kualiangzi landslide as an example, it is characterized by interbedded soft and hard rock beddings of low dip angles, and its evolution process can be mainly divided into three stages, namely, the stage of supergene reformation during formation of the valley, the stage of cracks expansion and time-dependent deformation and the stage of instability and failure of the whole slope caused by heavy rainfall. To deep-incision Xiangshuping landslide as an example, its evolution process can be divided into three stages, namely, the stage of supergene reformation during formation of the valley, the stage of time-dependent deformation, and the stage of sliding, bending and shearing. |
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