Early Warning Model Of Rainfall-induced Colluviums Landslides

The colluviums landslide, which occurs in the Quaternary system and the looseaccumulation, happens frequently in the Southwest China. The main characteristics ofthis kind of slide are wide distributed, high frequency of outbreaks and the continuedharming. A large proportion of landslide in China is this type. The slope structure ofcolluviums landslide is generally loose, strongly permeable and has high porosity.Because of all these characteristics, the rainfall and the groundwater become the mainreasons to lead the instability of the slope. In recent years, the environment isdeteriorating, and the extreme weather happens frequently. The heavy rainfall induceda host of colluviums landslides, which cause a great damage to people’s life andproperties. In all those reasons, it’s important to study the instability mechanism of thecolluviums landslide under the rainfall and to propose a early warning model ofrainfall induced colluviums landslide.On the basis of previous researcher, this article studied the seepage, deformationand failure rules of colluviums landslides under the rainfall condition by the modeltest and the numerical analysis.Furthermore, the author discussed the influence of different angles of slide bed tothe instability of slope, and proposed an early warning model of rainfall-inducedcolluviums landslides. The main research results are as follows:1. Summarized the general characteristics of the rainfall-induced landslide byaccessing a large amount of papers. And the author analyzed the instabilitymechanism of the rainfall-induced landslide.2. The model test of rainfall-induced landslides was proposed in the laboratory.And the result shows that:(1) There are two types of infiltration, along the slopesurface and along the internal cracks;(2) The volumetric water content and the porewater pressure are increasing during the rainfall and then steady after the peak. Thepeak of pore water pressure is decreasing with the increasing of the angle of slidingbed.(3) The deformation and failure process of the landslide is firstly in the samespeed and then accelerate, finally lose the stability instantly.(4) Under the same rainfall condition, the failure model is quite different under the different angel of slidebedding. When the angel is less than30°, the model is partial shallow sliding; whenthe angle is large than30°, the failure model is similar to block sliding.(5) The porewater pressure in different angles of sliding bed is a negative logarithmic function.3. Establish a finite element numerical model on the base of model test. And theresult shows that:(1) under the condition of rainfall infiltration, the pore waterpressure increasing with the depth of infiltration. And the highest speed of seepage isfound in the based cladding interface.(2) Comparing the results of pore waterpressure in the model test and numerical test. When the angle of slide bed is relativelyslow, the changing trends of are almost the same, but the pore pressure in numericaltest is smaller. When the angle of slide bed is relatively steep, the changing trends andthe values are all almost the same.(3) The analysis of landslide stability shows thatthe times of failure in both type of model are almost the same, and the phenomena arealmost the same, too.4. Established an early warning model of rainfall-induced colluviums landslideby the model test and numerical test. The pore water pressure, when the slope lossesthe stability, determines the total amount of water. And the total amount of waterdepends on the initial water amount of the slope and the cumulative rainfall. So thekey points to establish a warning model are the rainfall intensity and the rainfall time,which are relatively to the cumulative rainfall. Finally the author verified the warningmodel by Longjingwan Landslide.