Warning On Critical Displacement Of Accumulation Landslide

The accumulation landslide has the features of large quantities, wide distribution, sudden strong, serious harm. A strong earthquake tends to form a large amount of loose deposits. After the “4.20” Lushan earthquake in 2013, only in Baoxing county added more than 200 landslides and the accumulation landslide occupies considerable proportion. At present, the monitoring and early warning for the accumulation landslide is one of the commonly used methods of disaster prevention and reduction. To carry out the research of the early warning criterion of accumulation layer landslide is of great practical significance. Early warning of landslide displacement is a subject which is widely concerned by scholars at home and abroad, and it is also an issue worth exploring. Studies have shown that there is no universal critical displacement index for the accumulation landslide, but for a specific accumulation landslide, it is not only after the landslide deformation development to a certain extent. Therefore, in this paper, the critical displacement of the development process of landslide deformation is discussed and studied.In this paper, the evolution process of the landslide deformation is analyzed, and the critical displacement is defined. Taking domestic and foreign typical accumulation landslide as samples, through statistical analysis, using the quantitative theory I to construct the critical displacement prediction model of accumulation landslide. At the same time, the numerical simulation method is used to simulate the critical displacement of the landslide. Finally, the proposed method is applied to the typical landslide in Lushan earthquake area, and Putting forward the recommended value of critical displacement early warning. Achieved the following results and understanding:(1) The accumulation landslide deformation curve with three stage evolution. Research shows taking the displacement increment in the acceleration phase of landslide as the critical displacement of landslide is scientific and practical. The point in time of the critical displacement corresponds to the end stage of plastic deformation(accelerated deformation) of the landslide. With four parts includes creep displacement, compression displacement, plastic displacement and integral sliding displacement, which are related to the physical and mechanical properties, the length, the thickness and the slope of the landslide rock-soils.(2) Selecting the deformation pattern of landslide, landslide volume, length of landslide, landslide slope, sliding body thickness, landslide material composition, a total of six variables as the first grade indexes, to establish the critical displacement of landslide forecast index system, combined with the theory of quantification, the forecast index refining divided into 11 indicators. Through the correlation analysis, it is concluded that the indicators and the critical displacement of the landslide have good linear correlation, and the colinear problem among indicators is not very serious. Collected 36 cases of typical accumulation landslide in domestic as sample, constructing the critical displacement prediction model of accumulation landslide by using the quantitative theory I, and the goodness of fit and residual analysis to judge effect to prove the validity of the prediction model. According to the partial correlation coefficient of landslide critical displacement influence index, find that landslide critical displacement mainly depends on the geometric features of landslide, secondly the landslide material composition and thirdly the landslide deformation model.(3) Taking the Xintan landslide in the typical landslide as a case, based on finite difference method and selected the "feature point displacement catastrophe" as the criterion of instability, calculating the Geological-Mechanical-Deformation Model by shear strength reduction method. Obtained for each monitoring point reduction coefficient and displacement meets Exponential function equation: = a(?+), after analyzing and derivating obtained Xintan landslide critical displacement prediction value for 10.824 m, and very close to the actual monitoring value 9.1758 m. The research shows that the method of numerical simulation is feasible to obtain the critical displacement early warning criterion of the accumulation landslide.(4) Synthesize engineering geological analysis and numerical simulation results: The deformation of Shunshanlu landslide is mainly concentrated in the front of landslide, displacement decreases gradually from the slope surface to the inner part of the slope, at the foot of the slope shear stress is concentrated and likely to form shear opening. The main landslide is mainly shallow secondary sliding failure, integral sliding is unlikely, the failure mechanism belongs to "creep-crack" type, and the deformation development model for "traction" type. For precipitation-induced landslide, rainfall causes the matric suction decreases of the unsaturated zone in rock and soil is the main reason leading to the decline of landslide stability.(5) The critical displacement prediction model of accumulation landslide is applied in Shunshanlu landslide, obtains the overall landslide failure critical displacement warning suggested values for 1.8023 m, leading edge local failure critical displacement warning suggested values for 0.2860 m, is demonstrated by the prediction results are accurate. On the basis of landslide engineering geological analysis, combined with the critical displacement early warning criteria proposed in this paper, the method is reasonable, the technology is feasible, and the prediction result is accurate.