Study On The Formation Mechanism And Stability Of Guojiapo Landslide

The Longnan area of Gansu is affected by the Himalayan orogeny,and the neotectonic activity is very strong in the area.It is one of the landslide intensive activity areas in China.Guojiapo landslide is a typical one,and Guojiapo village was built above the landslide.Therefore,in this paper,Guojiapo landslide was regarded as the research object,and the engineering geological conditions of the landslide,the formation mechanism and stability were qualitatively and quantitatively analyzed,in order to provide a theoretical reference for the evaluation of the stability of the local landslide,which hadan important practical significance protecting the life and property security of Guojiapo villagers.The main conclusions of this paper are as follows:(1)Guojiapo landslide is 950~1100m long and 750 m average wide,and the volume of it is about 3750*104m3,so it belongs to a large talus landslide.The surface is cut by longitudinal gully,and the tensile fracture of loess on the trailing edge is developed.The sliding mass mainly consists of gravelly soil by eluvial slope covered pebbly loess soil and strong weathered limestone and slate,and the sliding bed is slate and limestone interbedded.The landslide has had four slides,the first time for the whole slope sliding,the second time for local sliding of landslide trailing edge,the third time for shallow slide of landslide posterior wall caused by Wenchuan earthquake,the fourth time for the sliding of leading edge caused by artificial slope cutting and rainfalls.(2)Comprehensive analysis shows that the strong tectonic activity formed the high and steep slope and fractured rock strata,concentrated rainfalls and human engineering and economic activities created the thick eluvial slope and weathered broken rock on the surface of slope,so the slope is likely to loose and broke in the strong vibration of southern Wudu earthquake,and then large-scale sliding occur under the dual forces of gravity and earthquake causing the diversion of Baishui River.The Wenchuan earthquake and the rainfall may cause the second sliding of the cliff of landslide trailing edge.(3)The stability of the landslide is analyzed using the limit equilibrium method and finite element method.The results show that the accumulations in front of the landslide are in stable state under the influence of three conditions ofnature,rainfalland smaller than IX seismic intensity,but the cliff of landslide trailing edge is in an unstable state under the condition of rainfall saturated and VIII seismic intensity existing further sliding tendency.(4)Analysis shows that the potential sliding zone caused by earthquake is located on the top of cliff,whose volume is about 164*104m3 and the threat scope is within 504 m in gliding direction;the potential sliding zone caused by concentrated rainfall is located in the upper part of landslide trailing edge,whose volume is about 96.5*104m3 and the threat scope is within 206 m in gliding direction.The necessary measures for disaster prevention and mitigation should be taken within the threat scope of potential landslides.