Influence Of Rainfall Infiltration On Stability Of Accumulated Landsides In Arid And Semi-arid Areas

The area with less rainfall in North and Northwest China is arid or semi-arid,and it is also the main distribution area of unsaturated zone.Most of the soil slopes encountered in the geotechnical engineering are in unsaturated state.In unsaturated soils,rainfall is often one of the most important factors inducing instability.At present,people have taken the coupling analysis of seepage field and soil skeleton deformation as the focus of slope stability research,but it has not really realized the seepage stress deformation coupling theory in the practical engineering slope stability analysis.Moreover,with China's "The Belt and Road" economic development strategy to promote economic construction scale in northwest region continues to increase,relates to the engineering problem of unsaturated soil gradually increased.Therefore,further research on the problems of fluid solid coupling in unsaturated soils is of great significance for scientific guidance and service in geotechnical engineering construction and geological hazard prevention.In this paper,taking the landslide of Xinghan village in Xingxian,Xingxian,Lvliang as the research object,the formation mechanism of the landslide in Shagou Miao village,Xingxian,was preliminarily discussed on the basis of the environmental geological conditions,morphological features and recent deformation and failure conditions.On the basis of the indoor soil test,the soil water characteristic curve is fitted,the VG seepage mathematical model is obtained,the soil water characteristic curve is given,the soil water characteristics and the deformation characteristics of the accumulated soil in the study area are analyzed,which provides the basis for the analysis of the accumulated soil rainfall infiltration.Geostudio and COMSOL Multiphysics are used to analyze the seepage field and the stress field by single and bi-directional coupling analysis,and the difference of unidirectional coupling and two-way coupling are compared,and the change rules of the seepage field and stress field and the stability change of the soil slope under rainfall infiltration are discussed.The main contents and results of this paper are as follows:(1)According to the environmental geological conditions of the landslide in the Shagou Miao village,the characteristics of landslides and the recent deformation and failure conditions,the formation conditions of the landslide in the Shagou Miao village in the Xing county are analyzed.The landslide of the Shagou Miao village in the impromptu county belongs to the Loess gravel base rock slope,and the deformation and failure mechanism is that the slope foot excavation destroys the balance about original stress of the slope.In addition,rainfall induces the sliding deformation of the leading edge of the slopeand the trailing edge cracking.And it belongs to the traction landslide.(2)Through the soil water characteristic curve test,with the aid of Origin data analysis software,the VG seepage mathematical model is fitted,and the soil water characteristic curve is given,which provides the basis for the multi field coupling analysis under the condition of unsaturated soil rainfall infiltration.The fitting model is applied to continue the simulation calculation.The soil water characteristic curves of different a and N are analyzed and compared.It is known that the larger n is worth the characteristic curve.When changing the a value,the smaller a value soil has larger inlet pressure value.(3)Take the Huatang landslide in Xing County as an example,using Geostudio and COMSOL Multiphysics finite element simulation software to conduct single and two-way coupling of the seepage field and stress field.The change law of seepage field and the evolution of stress field and stability under the conditions of rainfall infiltration are discussed.The differences between one-way coupling and two-way coupling are also compared.Analysing the influence of different rainfall conditions and soil saturation coefficient on the stability of the two fields and the slope stability,the main conclusions are:the rainfall intensity and holding time have a great influence on the seepage velocity,the rate of change of the matrix suction,and the location of the wet front.Considering the two-way coupling,the change of the pore water pressure in the slope is greater,and the coupling effect has a certain retarding effect on the rainwater infiltration.In the initial stage of rainfall infiltration,it is the timewhen the flow-solid coupling effect is the most obvious.Therefore,in the process of slope stability analysis,when the rainfall duration is short,the fluid-solid coupling effect must be considered.