Stability Mechanism Of Yili Loess Slope Under Multiple Freeze-thaw Cycles

The geological environment of the Yili River Valley is complex.At this stage,due to the rapid development of local urbanization and the sharp increase in human-land contradictions,geological disasters occur frequently in the Yili area,accounting for more than 80% of the total number of geological disasters in Xinjiang.This paper takes the loess slope in the upper reaches of the Ha Yindesayi debris flow valley in Xinyuan County,Yili Prefecture as the research object.Based on the national major special debris flow project management,combined with the local engineering geological conditions,the analysis of the strength degradation of the loess under the freeze-thaw cycle is discussed.The main controlling factors of the loess slope in the Yili River Valley were induced,and the stability analysis model of the loess slope in this area was established.The main achievements and understandings are as follows:(1)The geological disasters in the Ili River Valley are mainly landslides and dam-breaking debris flows caused by landslides.The deformation and damage of the slopes are mainly traction landslides.Under the action of freezing and thawing cycles,the slope damage is manifested as shallow freezing and thawing cycle spalling and thermal thawing karst As well as the evolution of mud flows,under the action of freeze-thaw cycles,the slopes are often fractured by plastic flow in spring.(2)During the freezing and thawing cycle,the apparent characteristics of the rock and soil are developed,and a large number of frost-like crystals and ice crystals develop.The more the number of kinetic volume cycles in the later period,the frost crystals begin to evolve into ice crystals.During the positive freezing period,the ice crystals appear in the vertical direction.Shape distribution,and cause hexagonal exfoliation on the surface of the sample.Deformation and damage are mainly laminar exfoliation.Expansion exacerbates soil exfoliation.During the positive melting period,the network ice crystals rapidly melt,and the increase in pore water pressure leads to the soil mass.The effective stress is reduced,and the thermal melting disturbance is generated to the surface rock and soil,and the disturbance degree is strong(3)Synthesizing the triaxial compression shear experiment under different moisture content and different freeze-thaw cycles,it is analyzed that the freeze-thaw cycle is a strong wind effect.After multiple freeze-thaw cycles,the spatial structure of the rock and soil changes.The water in the soil has migrated to varying degrees,and finally manifested as a significant decrease in the peak stress of the soil,and changes in the friction angle and cohesion in the soil.During the freeze-thaw cycle,the friction angle in the soil is due to the physical properties of the soil particles.The change is not large,the general range of change is between2%-7%,but the cohesive force fluctuates many times due to the water migration and morphological changes during the freeze-thaw cycle.(4)Under the action of freeze-thaw cycles,the mechanical strength of the surface frozen layer of the loess slope in the Ili River Valley changes,the slope stress distribution state,and the slope stability coefficient decreases.The sliding surface is mainly concentrated on the weathered layer,and the surface frozen layer hardly appears on the surface frozen layer.,Has a slight impact on the overall stability of the slope.