Evaluation Of Landslide Susceptibility In The Upper Reaches Of Xihanshui River Basin

The upper reaches of Xihanshui is located in the southwest of the Loess Plateau,adjacent to the northeast of the Qinghai Tibet Plateau.It is a transitional zone between the two geomorphic and tectonic units.Landslides and other geological disasters occur frequently.Based on the field investigation of landslide disaster in the upper reaches of Xihanshui River,this paper analyzes and summarizes the development and distribution law,influencing factors and genetic mechanism of all kinds of landslides.According to the development types of landslides,different methods are used to evaluate the susceptibility,and finally the superposition method is used to divide the susceptibility.The main understandings and conclusions are as follows1.According to the field geological survey,the landslides in the area are divided into three types: loess landslide,mudstone landslide and gravel soil landslide.Among them,there are 138 loess landslides,of which 13.7% are large landslides,46% are large landslides,34.5%are medium landslides and 5.3% are small landslides;51 mudstone landslides,of which 7.8%are large landslides,60.8% are large landslides and 31.4% are medium landslides;9 gravel landslides,of which 22.2% are large landslides,22.2% are medium landslides and 22.2% are small landslides 6%.2.The main factors affecting the landslide are the slope,slope shape,relative elevation difference,slope aspect,surface water system,stratum lithology,structure,vegetation and human engineering activities.The influence characteristics and degree of each factor are different with different landslide types.Among them:1)loess landslide is the most affected by slope and the least affected by road;2)mudstone landslide is the most affected by stratum lithology and the least affected by vegetation;3)gravel soil landslide is the most affected by slope and the least affected by river bank slope.3.The development process and mechanism of three types of landslides are different:1)Loess landslide.Because of the development of pores and cracks in loess,it is easy to cause slope instability and landslide under the condition of rainfall and earthquake;2)Mudstone landslide.The development of joints and fissures in the mudstone slope due to tectonic activity and weathering is easy to form weak zones under rainfall conditions,resulting in slope instability and sliding;3)Gravel soil landslide.Because there are many weathered and broken deposits on the surface of gravel soil slope,the physical and mechanical properties are very poor.Under the conditions of rainfall and earthquake,it is easy to cause the slope to slide along the top surface of bedrock and form landslide.4.Based on the landslide types,weighted information method,weighted certainty coefficient method and sensitivity index method are used to evaluate the susceptibility:1)The loess landslide prone areas are concentrated in the North Bank of Shuili Yanguan section of the Western Han Dynasty,the downstream banks of Shibao Township section of Yangshui River,shuijiangkou Township section of the Western Han Dynasty,and Lixian Luoba Township section of Yanzi River.The middle and low risk areas are mainly distributed in other areas of the study area;2)The high incidence areas of mudstone landslides are concentrated in the north of Yanguan town to the northeast of Lixian County,the medium and high incidence areas are concentrated in Lixian Yongping Township,and the other areas are mainly medium and low incidence areas;3)The high incidence areas of gravelly soil landslide are concentrated in Lixian Yongping Township,while the other areas are mainly medium and low incidence areas.5.The susceptibility assessment results of the three types of landslides are further superimposed to determine the susceptibility zoning of landslides in the area.On the whole,according to the degree of susceptibility,it can be divided into high risk area,medium high risk area,medium risk area,low risk area and non risk area.Among them,high and medium high risk areas are concentrated in the transition zone from Valley terrace to loess hilly area,medium risk areas are concentrated in loess hilly area,and low risk areas are distributed in other areas.