Research On Forecasting Methods Of The Loess Landslide With High Speed And Long-run Distance

In view of the reality that the loess landslides with high speed and long-run distance occurred frequently, it is of very important significance to develop the forecasting research of landslide disaster in theory and in practice, under the present economic and technical conditions that they couldn't been controlled thoroughly, which is also a focus and difficulty issue in the world. Based on the previous researches, taking the high-speed and long-run-distance loess landslides belt—one of the most serious landslide disaster belts in Guanzhong basin of shaanxi province—which lies on the south bank of Jinghe River in Jingyang County as research object, this paper studied the strength characteristics of the loess landslides with high speed and long-run distance through the experimental analysis of slide soil, and researched the spatiotemporal forecast methods systematically by adopting statistical model, kinematical model and creep model. Some achievements obtained are in the following several aspects:(1) The slide belt soil is of the control effect in forming, developing and scale of the high-speed and long-run-distance loess landslides. Many kinds of testing methods and research tools were used to study synthetically the shear strength characteristics of the slide zone soil on 5 aspects such as peak strength, residual strength, softening strength, long-term strength, and starting strength."Property strength"and"state strength"are newly proposed in the paper to explain their properties of all strength characteristic parameters of loess landslide and their relationship, the author in the paper considers that: the peak shear strength is a kind of"state strength", correlating mainly with the loess's structural strength and water content of non-saturated loess. Residual strength and softening strength are both kind of"property strength", which is mainly related to soil property index , such as the clay content, the mineral component and the plasticity index and so on, and some correlations are established among them through which shear strength could be better obtained by adopting the conventional test indexes. A result of the microscopic structure's research analysis (by SEM) to the slide zone soil has confirmed the acquaintanceship obtained.(2) Proposed the concept of"starting water content"of landslide. The slide zone loess's peak strength displays the characteristics that its strength, in certain lower water content scope, reduces slowly along with the water content's increasing; and plummets rapidly along with the water content's increasing when water content reaches a certain point. Which can explain that landslide obtains the condition of high-speed starting; its corresponding peak shear strength is the landslide's starting strength. The test and back analysis indicates the plastic limit water content of the Jingyang landslides'slide soil is the starting water content of them. Based on concept of"starting water content"of landslide, the paper analysis the mechanics mechanism of the loess landslides with high speed and long-run distance in Jingyang area, which is a kind of synthesis reflection of the strength's plummeting rapidly to cause high speed starting, the slide zone's liquefication, as well as the"roller effect"and so on.(3) As to landslide space forecasting, through the surveying on Jingyang south plateau loess landslide belt on the spot, each characteristic parameter before or after slope sliding is obtained. One-dimensional or multi-dimensional statistical model of the sliding distance of loess landslide with high -speed and long-run distance are established based on the characteristic parameters; the Scheidegger forecasting formula and the Xiesong K. forecasting formula are proved the same theory built on the"stilts slope"(H/L) essentially, they also have a fine linear relativity forecasting result in the loess area's, and its modified forecasting model is obtained.(4) Paper has established two kinematics models based on the function conservation and considered of the slide zone soil strength parameters: One of them is a simplified kinematics forecasting model based on the energy conservation, the consideration of characteristic landslide movement and the strength property of slide zone soil, this model fully considers the strength property during the moving of landslide, the concrete formula and the forecast technique are provided. Another considers the influence of pore-water pressure during sliding and of the slide zone's liquefaction; based on the speed and slips in the prognostic formula proposed in the predecessor; the modified forecast equation is obtained.(5) Conducted the research on creep property of the slide zone soil, and established slide zone soil creep empirical equation in this area, discussed the inner link between loess creep property and the landslide jitter, explored the feasibility of Saito model in the loess slope time forecasting, and proposed one estimate method of landslide time forecast based on the creep theory.