Characteristics Of Strength And Effect Of Loess In Yili Valley Under Dry And Wet Circulation

With the policy response of the "Silk Road Economic Belt" in the new era,the urbanization construction and agriculture and animal husbandry of the Yili River Valley have developed rapidly,and the contradiction between human production and construction activities and the geological environment has increased sharply.From 2005 to 2020,the Yili River Valley area A total of 339 geological disasters occurred,including233 landslides.This paper takes the H8 landslide body on the west side of Hayindesayi gully in Xinyuan County,Yili County,Xinjiang as the research object,and passes through the dry-wet cycle(0 times,1 times,3 times,5 times,7 times,9 times)Direct quick shear test,soil shrinkage test,microstructure test test and numerical simulation simulation to study the strength degradation characteristics,shrinkage deformation characteristics,microstructure changes and slip-promoting effects of Yili loess under dry-wet cycles.The main research contents are as follows:(1)According to indoor rate of water content test,density test,particle analysis test,limit moisture content test and proctor compaction test,etc.,we have the physical properties of loess in this area.which are the strength degradation and sliding promotion effect of Yili loess under subsequent dry-wet cycles Experimental research provides a research basis.(2)Through direct fast shear tests under different cycles,the stress-strain relationship curve,shear strength and shear strength parameters under different cycles are obtained.The relationship between the number of wet and dry cycles and the shear strength is analyzed,and it is concluded that with the increase of the number of wet and dry cycles,the shear strength and cohesive force show a decreasing trend,and the amplitude is the largest after one wet and dry cycle,but the internal friction angle Shows fluctuating changes.Finally,the shear strength and the degradation of shear strength parameters are calculated,and the law of the strength degradation of loess under the conditions of dry and wet cycles is obtained.(3)Through the soil shrinkage test under different number of dry and wet cycles,to study the water loss shrinkage deformation characteristics of Yili remolded loess after different numbers of dry and wet cycles,and obtain the change law of its moisture content and linear shrinkage rate with time.And obtain the shrinkage curve,it is concluded that as the number of cycles increases,the final shrinkage rate and shrinkage coefficient of the soil show a decreasing law.It is determined that the boundary moisture content of the soil in the straight-line shrinkage stage,the curved shrinkage stage and the approximate horizontal straight-line shrinkage stage are 12% and 8%,respectively,and the shrinkage limit of the Yili loess is 8%.(4)Scanning electron microscopy(SEM)and nuclear magnetic resonance(NMR)techniques were used to study the microstructure parameters of particle size,pore diameter,pore area ratio and pore volume were selected as the quantitative analysis parameters of microstructure.The results showed that with the increase of drying and wetting cycles,the content of large and medium-sized particles showed a downward trend,while the content of small particles showed an upward trend;the content of large and medium-sized pores showed an upward trend,while the content of small pores showed a downward trend The results show that the content of pores decreases,the proportion of pore area increases,the volume content of macropores and mesopores increases,and the volume content of micropores decreases.The micro process of strength deterioration of loess is revealed,and the microstructure explanation of macro deformation and instability of Yili loess slope is obtained.The correlation between micro characterization parameters and mechanical strength of loess is obtained.(5)Based on the field investigation of geological environment,the evolution model of loess slope is generalized.According to the shear strength parameters obtained from direct quick shear test,the strength reduction method is used to simulate the variation characteristics of slope stress,displacement and safety stability coefficient under three working conditions after different dry wet cycles by ABAQUS.It is concluded that with the increase of dry wet cycles,the stability coefficient of the slope presents a trend There is a downward trend.