Influence Of Coupling Of Rainfall And Earthquake On The Stability Of Dalin Landslide

Dalin landslide is located in Shimian County,Ya'an Yonghe Township,village of Dalin.The region is a typical mountain canyon,the gentle slope area covered with thick residual slope;The average annual precipitation in the region reached 1200.9mm;The area is located at the junction of the Xianshuihe Fault Zone and the Anning River Fault Zone,and near the Longmen Mountain Fault Zone,so earthquakes occur frequently.Dalin landslide is a typical landslide affected by rainfall and earthquake,so the study of regularity of stability of Dalin landslide in rainfall,earthquake and coupling of rainfall and earthquake is very necessary,it can also provide a reference for the stability analysis of similar landslide in this area.This paper takes Dalin landslide as the research object,through field investigation,combined with drilling and other exploration means,to identify the boundary conditions,landslide slip zone depth,morphological characteristics,deformation characteristics and landslide composition;On the basis of finding out the basic conditions,the deformation and failure mechanism and evolution process of Dalin landslide are analyzed;The field test and indoor soil test of Dalin landslide were carried out;The seepage field and stability of Dalin landslide under different rainfall conditions were analyzed by Geo-studio;The stress field,displacement field,plastic zone and shear strain increment of Dalin landslide are analyzed by FLAC3D;After theoretical analysis,the stability and seepage field of Dalin landslide under the coupling of rainfall and earthquake are analyzed..The main conclusions are as follows:(1)Dalin landslide belongs to Zhongshan Valley landforms,steep slope,slopes for polygonal terrain on both sides raised among the low-lying,flat fan-shaped,sliding body is mainly silty clay with fragments of stone,the total volume is about 750×104m3,the landslide direction is 70 degrees;(2)The middle and upper bedrock of Dalin landslide is Triassic sandstone by drilling,in the lower part of the bedrock is third Xigeda silty sandstone and clay rock,which has weak water permeability,it acts as a barrier to water,it conducive to the enrichment of groundwater in landslide,have an adverse effect on the stability of landslide;In situ double loop permeability test,the permeability coefficient of sliding mass was measured,which is of medium grade;(3)The structural part of the Dalin landslide belongs to the vicinity of the nucleus of the double fold anticline,on the west side of landslide at 1km is Meiluo fault;(4)There are 6 obvious collapses and many cracks in the landslide,the calculated stability coefficient is 1.145 by using the limit equilibrium method in the natural state,the calculated stability coefficient is 1.13 by using strength reduction method,the results are basically the same,the landslide is in stable status;(5)According to the local meteorological conditions,the variation law of seepage field and stability of Dalin landslide under different rainfall conditions are analyzed,draw the following conclusions:(1)At the same time of rainfall,the greater the rainfall intensity,the greater the negative pore water pressure contour,at the foot of the water line was higher.,the lower the stability of landslide;(2)Under the same rainfall intensity,the longer the rainfall,the more infiltration of rain water,the higher the groundwater level rise,the smaller the matric suction in the slope,the smaller the stability of the landslide;(3)In the same rainfall condition,it is easier to infiltrate into the slope due to the small intensity and long duration rainfall,the effect of increasing load and softening of rock and soil is more obvious,landslide stability is lower;Rainfall with large intensity and short duration is easy to form transient saturated zone on the slope,rainfall infiltration on slope table is hindered;(4)After the rain stops,surface water on the slope will continue to seep,the stability coefficient of landslide continued to decrease in a certain time;The transient saturation zone of slope surface will disappear gradually and negative pore water pressure increases gradually;(6)According to the local earthquake situation,the variation of stress field,displacement field,plastic deformation zone and shear strain increment of Dalin landslide under different earthquake accelerations are analyzed,draw the following conclusions:(1)In the middle of landslide sliding bed parts of stress concentration,the greater the earthquake acceleration,the stress concentration phenomenon is obvious;There is a small area of tensile stress in the surface of the landslide,seismic acceleration is larger,the larger tensile stress;(2)With the acceleration of the earthquake,the displacement of Dalin landslide in both horizontal and vertical direction increases gradually,and the stability of landslide is lower;(3)The plastic yield zone appears in the slope under seismic action,the landslide mainly produces shear failure;Earthquake acceleration is bigger,the plastic yield zone area is larger;When the earthquake acceleration is 0.2g,the shear plastic zone to be opened,the landslide is in unstable state;(7)The coupling effect of Dalin landslide after the first rain and the coupling effect of rainfall after the first earthquake are analyzed,draw the following conclusions:(1)The stability of the earthquake after rainfall is lower than that under the natural condition;The stability of rainfall after earthquake is lower than that of natural rainfall;The effect of rainfall on the stability of the landslide is greater than that before the earthquake in state of coupling effect;(2)Under the same earthquake acceleration,the higher the moisture content of the landslide,the greater the tensile stress area of the trailing edge of the landslide,the greater the tensile stress value,the larger the maximum displacement and the smaller the stability of the landslide;(3)After the earthquake,the permeability increases and the groundwater level decreases.The greater the seismic acceleration,the stronger the permeability of the sliding body,and the more stability of the landslide after the same rainfall condition;(4)After the same earthquake acceleration,the greater the rainfall intensity,the more negative the value of the negative pore water pressure,the higher the groundwater level rise,the more detrimental to the stability of the landslide;(8)The Dalin landslide has a slow creep sliding to the front of the slope,there is a trend of overall subsidence on the slope,tensile cracks appear at the trailing edge and the height of the rock slope at the trailing edge of the sliding body increases gradually,it can be concluded that the deformation and failure mode is creep-crack type.