| Xining,located in the Huangshui River Valley at the eastern edge of the Qinghai-Tibet Plateau,is the central city of the Ancient"Silk Road"South Road and the cradle of hehuang culture.In recent years,continuously from the plains to the hilly mountain city expansion,the large-scale infrastructure construction and human engineering activities such as irrigation water diversion greening destroyed the hilly mountain landscape resources and geological environment,makes the precipitation induced geological disasters and frequent happens,soil and water loss,serious threat to people's life and property security,becomes the bottleneck of social and economic development and national spatial planning problem.Xining city is divided into low hills and valley plain area.The strata of low hills and hills at the edge are mainly composed of tertiary mudstone,gypsum rock,sulfate chemical sedimentary layer and salt rock interbedded with quaternary loess.The soft and hard horizontal strata structure resulted in an almost vertical steep wall of bedrock between the mountain and the terrace.Differential weathering leads to the spalling of mudstone and the collapse of sandstone without support,so a large amount of colluvial soil is accumulated under the bedrock slope.The colluvial soil is a mixture of mudstone,gypsum and loess with complex material source,composition and structure,low strength,high deformation and poor stability.In this paper,CT scanning technology,high-density resistivity geophysical exploration technology,AVIZO image processing software and Geo-Studio numerical simulation software were used to conduct experimental research on physical properties and numerical simulation of xining colluvial soil by combining field investigation and laboratory experimental research.The main research results are as follows:(1)Physical and mechanical tests of 15 groups of colluvial soil show that the structure of Xining colluvial soil is loose and its porosity is 30.7%?37.6%.The soil has strong permeability,and the permeability coefficient is 0.98×10-4?1.65×10-4 m/s.The soil particles are mainly silt and clay,and contain fragments of salt rock and mudstone.The soil is not uniform and has poor sorting ability,and the grain size increases gradually from top to bottom along the slope.The shear strength of colluvial soil is small,the cohesive force is 4.1?14.3 k Pa,and the internal friction Angle is 24°?35°.(2)Microscopic pores of colluvial soil were identified and quantitatively characterized by CT scanning and AVIZO image processing system.The results showed that the pore size of colluvial soil was 0.1?0.5 mm,accounting for 72.38?76.26%of the total pore size.The pore volume with a pore diameter of 1 to 5 mm accounted for the largest percentage of the total pore volume,which was 53.49 to 55.71%.The porosity on the micro scale is between 21.7 and23.4%.The pore throat radius was mainly less than 0.1?m,and the number of pore throates in this interval accounted for 60.52?84.02%of the total number.The pore throat length was concentrated in 0.5?1?m.The average value of pore throat tortuousness was 1.18,and97.60?97.81%of pore throat tortuousness was concentrated in 1?2,indicating small pore resistance and good permeability.In colluvial soil,the distribution of pores is uneven,the size is different,and the distribution is often concentrated,which makes it easy to form preferential channels in the seepage process.(3)The slope geology and lithology structure of the colluvial soil in the study area are complex,and the difference in resistivity provides a physical prerequisite for the high-density electrical method to explore lithology in the study area.The resistivity sounding section is arranged on the slope of a colluvial soil in linjia Ya geological hazard zone,and the exploration line is 500 m long.Combined with the data of geological boreholes and using the apparent resistivity pseudo-sectional drawing of the survey line,the slope geological structure model of the colluvial soil is established by inversing and infering the mudstone basement below the surface loess,sand gravel,subsand and colluvial soil in the depth direction.(4)Seep through the Geo-Studio software module,the colluvial soil slope seepage under the different rainfall condition,the results show that when the same rainfall with different rainfall intensity,slope of pore water pressure in the body with the increase of rainfall intensity,rainfall at the end of the pore water pressure will continue to increase,but increases at a slower pace,showing a certain lag,pore water pressure in the rain for 2?3 days after the end,but you can't back to the previous numerical rainfall.(5)Limit equilibrium method is used to analyze Slope stability of colluvial soil by Slope module of Geo-Studio software.The results show that the greater the rainfall intensity is,the faster the Slope stability coefficient will decline.The rainfall intensity was 80 mm/d.On the third day of continuous rainfall,the slope was unstable and damaged.When the rainfall intensity was 20 mm/d and 40 mm/d,the stability coefficient decreased first and then increased after the end of rainfall,but failed to return to the stability coefficient value before rainfall.The parameters that affect the stability of the slope are internal friction Angle,cohesion and bulk density according to the sensitivity from large to small,and the corresponding sensitivity is0.122,0.107 and 0.018 respectively.(6)According to geo-studio displacement simulation,under the infiltration condition of rainfall,the slope of colluvial soil tends to slip towards the foot of the slope,accompanied by vertical subsidence.The displacement of the slope was concentrated in the accumulation part of the colluvial soil and the foot of the slope.Under the condition of rainstorm,the slope is at risk of instability,and the sliding position is most likely to occur on the contact surface between the accumulation part of the colluvial soil and the sandy mudstone.The loose structure and good permeability of the colluvial soil cause the infiltration of a large amount of rain water,softening and sludging of the sandy mudstone in contact with water for a long time,reducing the shear strength,forming a soft sliding zone and inducing the occurrence of landslide disasters. |
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