| In recent years,due to the intensification of human engineering activities,landslides and collapses have become more frequent in Lanzhou area.According to relevant statistics,loessmudstone landslides account for about one third of all types of landslides,so it is urgent for us to study the softening characteristics of mudstone in Lanzhou area,and then analyze the mechanism of loess-mudstone landslides.This paper takes the loess-mudstone landslide of North Ring Road as the research object,and combines the field investigation data,laboratory test data and the landslide deformation simulation results of Midas/GTS NX finite element analysis software,and studies the development characteristics,failure modes,deformation characteristics and stability of the landslide of North Ring Road.The main conclusions are as follows:(1)The main controlling factors of landslide formation in North Ring Road are high and steep slope topography and special geotechnical structure;the main inducing factors of landslide are persistent rainfall in the early stage of landslide,long-term seepage caused by hillside greening irrigation and slope foot excavation and slope unloading caused by highway construction.(2)In order to study the influence of mudstone softening characteristics on the development of landslide,a water-immersion softening test was carried out on mudstones of the same strata as the sliding zone,and then the mineral composition,microstructure and mechanical parameters of mudstones with different immersion time were analyzed by relevant experiments.The results show : After mudstone is immersed in water,clay minerals swell and absorb water,resulting in serious softening and disintegration of mudstone,and eventually the whole structure of mudstone becomes very loose;after mudstone immersion,clastic minerals decreased relatively,while clay mineral content increased slightly,indicating that water-rock interaction had a certain impact on the mineral composition change of mudstone;under longterm immersion;the mechanical strength of mudstone decreases greatly under the action of long-term immersion.(3)In order to study the shear strength properties of slip zone mudstone,this paper designs ring shear tests with different shear rates and different shear modes;the influence of shear rate on shear strength is that the shear parameters of peak strength of mudstone in slip zone change significantly with shear rate,while the parameters of residual strength change little with shear rate;compared with single-stage shear test,pre-shear test and multi-stage shear test can effectively reduce the shear displacement required to reach the residual strength,and the residual internal friction angle increases,while the residual cohesion decreases slightly.(4)Based on the analysis of the development characteristics,controlling factors and inducing factors of the landslide in the North Ring Road,this paper considers that the landslide types are loess-mudstone landslides of thrust type and shear type.Typical landslide sections are selected and the deformation and failure characteristics and stability of landslide are analyzed by Midas GTS/NX finite element software.The simulation results are consistent with the actual deformation and failure characteristics of landslide.Based on the above analysis,this paper considers that the deformation and failure mode of the North Ring Road landslide can be divided into four evolution stages: incubation stage,cracking stage,creep stage and sliding stage. |
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