Research On The Mechanics Of Rainfall-triggered Loess Landslide In Yanan District, Shaanxi

The mechanics of the rainfall-triggered landslide is one of the key topics inthe academic and engineering circles. Meanwhile, it is also a difficult problemdue to the failure of finding out the regularity of water migration in soil and theimmaturity of the unsaturated theory. However, the rainfall-triggered landslide iseasy to occur, so we should solve the problem as soon as possible. Consequently,the further exploration of this filed has actual significance.The main contents and results of this research as following:(1) In this paper, the mechanics of loess landslide triggered by rainfall isresearched on the theories of unsaturated, saturated soil mechanics andunsaturated seepage, meanwhile, the LS-rapid is applied to simulate the processof the loess landslide motion. Based on this, a method system, which from thein-situ observation research on the regularity of water migration in loess, to thesuction measurement in the laboratory, to the classification of the types of thewater infiltration, to the simulation of the slope failure, to the simulation of theloess landslides motion, to the prediction of sliding distance. (2) The in-situ observation of the regularity of water migration in loessshown that as rainfall intensity is about10mm/d, depth influenced by waterinfiltration is less than0.3m. However, after rainy season of concentratedprecipitation, part of the precipitation infiltrates into the loess and migratesfurther to a deep position. The water migration in the soil above3m is swift, butslows down with the depth increasing. As encountering a relative poorpermeability bed, the water would gather on the bed to increase water content inthe loess. For impervious bed, water content increases accumulatively withinfiltration supplies of the intermittent precipitation. This phenomenon mayreveal the mechanism of the loess landslides induced by rainfall or irrigation.(3) Based on the results of the field observation, the test in and out oflaboratory, the development features of the loess landslide under different typesof rainfall infiltration are analyzed, which includes the shallow landslideinduced by the water infiltrate through the micro-pores and joints of loess, thelarge scale landslide induced by the water filling in the open cracks and sinkholes on the top of the slopes, and the he large scale landslide triggered by thelong period of water infiltration. Three typical landslides of the different types are chosen, and then analyze the transient seepage by the SEEP/W. Based on theresult of seepage analysis; the nodes stress of slide surface was analyzed by theSIGMA/W. The method mentioned above shows the essential mechanic of theloess landslide formation. At last, the stability of the slopes is calculated by thelimit equilibrium method for the intuitive explanation.(4) According to the LS-RAPID exploited by Sassa, the typical loesslandslides are simulated, the value of the residual friction angle is obtained bythe repeated shear test under the undrained condition. The analysis will be usefulto predict the sliding distance.