| Landslide is one of the common geological disasters in China,especially in southwest China.Landslide is highly harmful which causes are complex.The rainfall is one of the main factors of landslide deformation and failure.Qinganglin landslide is located in Gaoqiao Township,Nanjiang County,Bazhong City,in the southeast-northwest between the two ditches,the front edge of the ditch to form a wide narrow terrain,southwest high northeast low,and the ramp surface is a loose stack.According to the investigation of the Qinganglin landslide,it is known that the landslide occurred in the rainy season,and each time a new deformation and the deformation increasedoccurred in case of rainfall.At present,there is no further study of the stability of the landslide under rainfall conditions.Therefore,it is necessary to research the stability of the landslide under rainfall conditions.In this paper,the Qinganglin landslide is taken as the research object,through field geological survey methods and geological drilling methodsthe boundary,scale and shape characteristics of landslide,as well as the material structure and deformation characteristics of the landslide mass are found out;Through field test and indoor mechanics test the permeability and physical and mechanical parameters of the Qinganglin landslide are obtained;Then,the variation of seepage field of green bar landslide is analyzed;Finally,the change of the stability of the Qinganglin landslide are analyzed by the limit equilibrium method and the strength reduction method.The recognition and conclusion are as follows:(1)Qinganglin landslide belongs to the low mountain landform,the plane formed a long tongue,had regular shape,the main sliding direction is 340°,bulging deformation of lip landslide soil,housing wall at central boundary dumping,and the trailing edge of the landslide has slope collapse and residual slope accumulation.The longitudinal length of the landslide is about 240 m,with a width of 150 m,a total area of 36000m2,the average thickness is about 9m,the scaleis about 324000m3,it is a middle-sized soillandslide of creep rip type.(2)The stratum lithology and physical structure of the landslide are revealed by drilling,and the sliding mass is divided into two layers,the upper part is generally purple-red clay with a small amount ofstone fragments,the lower part isfragmentsoil,the main composition of the parent rock of the sliding mass is sandstone,siltstone,mudstone,etc;The stratum lithology is mudstone and sandstone interbedded in the Penglai formation of the upper Jurassic(J3P),and from top to bottom was full-strong-weathering.(3)The site survey shows that the Qinganglin landslide is a new landslide,and the middle part of the landslide is basically stable,but there are different degrees of sliding deformation in the rear and front of the landslide.The rear of the landslide is slope collapseaccumulation which is dominated by large stone,the diameter of the rock is 20-80 cm,the main rock is mainly composed of sandstone and accumulates on the right rear side of the landslide;The deformation of the front of the landslide is obvious,the soil is bulging and deformed,the Ridge of fieldfell,and there are water leakage phenomena,the road surface collapse and the crushing and destruction are obvious;There are more than 10 cracks developing on both two sides of the landslide,which are ranging from a few meters to tens of meters range and the width of 10-20 cm,there may be the overall sliding instability(4)By in situ double loop permeability test the permeability coefficient of the landslidesoil was obtained,the result is 1.52 10-3cm/s~1.96 10-3cm/s,which belongs to moderate permeability.The atmospheric precipitation is easy to penetrate into the landslide body,so that the groundwater of the landslide is well supplied,however,due to the low permeability of the underlying bedrock,the relative impermeable layer is formed,which makes it easy to enrich in the sliding bodyafter rainfall infiltration;The result is the shear strength of the soil decreased,and cause the adverse impact to the stability of the landslide.(5)The groundwater tracer test was carried out to obtain the average velocity of groundwater in the slope,the application of this kind of test in landslide is very fewthe result is about 0.79m/h.The result shows that the groundwater in the tracer test is runoff along a specific channel,which can be surmised as the sliding surface of the landslide.So when there is rain,rain infiltrate to Qinganglin landslide can seepage along the slip surface and further reduce the slope stability,and accelerate the deformation and failure of the landslide.Groundwater tracing test designed in the Qinganglinlandslide body can provide the basis for the qualitative analysis of the deformation and failure of landslide.(6)According to the local meteorological conditions of the study area,the author designed different rainfall programs,and analyzed the changeregulation of the groundwater seepage field of the Qinganglin landslide,the results are as follows:(1)When rainfall time is the same,the rainfall intensity increases,the pore water pressure contour changes from the linear distribution to the curved distribution,and the negative pore water pressure decreases gradually,when the rainfall intensity is greater than the permeability coefficient of soil,the soil is in a state of transient saturation,after that there is no obvious change of pore water presure;(2)When the rainfall intensity is constant,with the duration of rainfall,the matric suction of the landslide surface layer decreases,and the matric suction closure area gradually decreases until it disappears,at the same time,the groundwater level rises gradually;(3)During a heavy rainfall,the groundwater line was raised at the foot of the slope;After the rain stopped,it is still seepage in the slope,the matric suction closed area gradually linked up and disappeared,and the pore water pressure contour gradually became a linear distribution,the groundwater gradually returned to the natural state;(4)Under the condition of the same total rainfall when rainfall intensity is small,and the rainfall duration is long,it is more easily infiltrated into the landslide,however,when there is a short time heavy rainfall,the surface soil is easy to reach saturation and rainfall infiltration is not sufficient.(7)Designed different rainfall programs to analyzethe stability of the Qinganglin landslide,its changeregulation is as follows:(1)With the same rainfall time(48h),the landslide stability coefficient decreases with the increase of rainfall intensity;In the early stage of rainfall(12h),the reduction rate is small and the greater the rainfall intensitythe greater the reduction rate;(2)When the rainfall intensity is the same(18mm/d),the landslide stability coefficient decreases with the increase of rainfall duration,but the landslide body is in a basic stable state;(3)During the process of a heavy rainfall(117mm/d)the stability coefficient of the landslide is decreasing;After24h the rain stopped,the stability coefficient of the landslide decreased to a minimum(1.04),the landslide was in a less stable stateand showed a slow upward trend after 48 hours;(4)When the total rainfall amount is the same(230mm),the difference of stability coefficient of each kind of rainfall combination is small.The stability coefficient of the landslide is the least in thecase of the combinationof small rainfall intensity and long rainfall duration,and also the most unfavorable to the stability of landslide.(8)Through strength reduction method of FLAC3 D software to analyze and comparethe stability of the Qinganglin landslide under the condition of natural state and rainfall,the distribution regulation of displacement field and stress field areobtained,andunder the condition of 3 days rainfall amount 136 mm,it is under steady state. |
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