Study On The Mechanism Of Shallow Surface Spalling Of Residual Soil Slope In Short Time Frozen Area

The soil in the short-term frozen soil region has the characteristics of short freezing thawing cycles,frequent freezing thawing times and shallow frozen soil depth in winter.Under the action of frequent freezing and thawing,the slope soil presents a large number of shallow surface spalling instability.The phenomenon of peeling off soil has caused great trouble to local traffic,but the related research has not been paid attention to.In my research,methods by using laboratory test,numerical simulation,combined with the theoretical analysis,explore the short-time permafrost residual soil mechanical properties of macro and meso damage law,frost heaving characteristics,soil slope instability of scour off.Specific research work and achievements are asfollows:1.According to the cause of the investigation,the typical spalling hazard of short-term frost zone is divided into three types:freeze-thaw type,spalling type and mixed type,according to the cause of the investigation.2.By freeze thawing soil after three axis test,the mechanical parameters of remolded soil increased with the increase of the number of freeze-thaw cycles and decrease exponentially,and after 6 freeze-thaw cycles were essentially the same mechanical properties;four after freeze-thaw damage,including elastic modulus,cohesion,angle of internal friction loss the maximum respectively accounted for 8 of the loss amount of 81.54%,94.48%,61.32%;fitting the damage model of freezing and thawing on the macro mechanical parameters of soil.3.Based on the results of the three axial test,the simulation of the flexible boundary is carried out in the simulation of PFC three axial compression test,and the freeze-thaw damage law and the meso failure process of soil structure are analyzed.The study found that the laminated wall can simulate flexible boundary,and the porosity,stress,particle displacement angle accurately reveal the structure of soil meso damage process;particle normal stiffness,tensile strength,friction coefficient decreased with the increase of freeze-thaw cycle was decreased,and the damage of consistent and soil macro parameters damage the damage were concentrated in four times of freeze-thaw cycles,and the corresponding damage formula fitting.4.By setting the ice particle radius expansion,stress release and stop operation criterion,optimize the current PFC freezing process simulation method;frost heave design indoor test calibration of soil ice,Bing Bing cementation and micro parameters,and then reveals the microscopic characteristics of frost heave residual soil column and slope.Research shows that the swelling soil porosity in the heave process mainly from ice particles,moving to reduce soil column lower porosity,middle porosity unchanged,upper porosity increases;frost effect only reflects the layered pressure in the vertical to the slope frost;frost heave by 45 degrees,slope angle and slope toe in turn transverse displacement,displacement and the formation of the two affected zone gradually to the slope expansion;60 degree slope displacement influence area only from the angle of slope rock slope extended;reduce the disturbance effect on the slope of soil frost heave.5.Three axis test data based on biaxial simulation calibration of soil parameters;considering soil fine freeze-thaw damage view parameters,and applied on the slope surface runoff velocity and particle increase severe rainfall can simplify the PFC2D process simulation,and analyzes the short-term frozen area of mixed type slope spalling rule.The results show that the freezing and thawing damage of soil meso scale parameters increases the amount of erosion and erosion,and the erosion amount of 45 and 60 degrees slope increases by 87.35%and 47.2%,respectively.