Study On The Mechanics Of Rainfall-induced Landslide And Its Evaluating Method

More than 60% of landslide is due to rainfall. The research of the mechanics of rainfall induced landslide and its evaluating method is a problem which is difficult to be solved and interested by academic field and engineering field. However, there are not research findings which can be used. For this reason, the research in this aspect is of great significance in the aspect of theory and engineering.The main contents and results of this research as following:(1) In this paper, the mechanics of rainfall induced landslide and its evaluating method is researched according to theories of unsaturated soils mechanics and saturated-unsaturated seepage. Based on this, a method system, which from the field observation of suction, to unsaturated soils mechanics test in laboratory, to analysis of mechanics of model, to the saturated and unsaturated seepage field in the slope under the conditions of rainfall is analyzed by numerical simulation method, to the slope stability valuating, is established. From XieTan landslide in SanXia reservoir area, the effect of rain on the slope stability is studied by above research result.(2) In this paper, mathematical models of soil-water characteristic curve are studied and divided into four types by the patterns of mathematical models. Based on this, universal mathematical model with unified functional pattern is derived from four types by the patterns of mathematical models, and universal mathematical model is researched by the test data of soil-water characteristic curve of unsaturated soils in XieTan landslide and loessal soils in north ShanXi loess plateau.(3) In this paper, the effect of suction on the stress —strain behavior of unsaturated soils is researched. Based on this, the mechanics and the regularity of the displacement of slope due to rainfall are researched according to the viewpoint of strain behavior of unsaturated soils due to suction. The displacement of slope due to rainfall is relation with suction and the stress —strain behavior of unsaturated soils is put forward, and the moisture content —the strain behavior of unsaturated soils is build. The exponential relationship of the displacement of slope and rainfall is analyzed and verified by this theory, from the Wu Du landslide.(4) The field observation of suction in the landslide is very important for studying the criterion of the landslide instability induced by heavy rainfall in terms of the theory of unsaturated soil mechanics. It is essential to build a description of suction variation with depth in a landslide. For this purpose an observation well was constructed and almost 16 months observation data have been obtained. The analyzing of these data gives us flowing ideas: (1) Suction variation with depth in a landslide is controlled by the landslide structures and its material composition, and it is different from that described by some other authors. (2) The variation of Suction with rainfall in a landslide has a correspondence with primary rainfall at upper part of unsaturated zone, but the situation is quite different at middle and lower part of the...