Research On The Mechanism Of Frost-heaving Damage In The Deep Foundation Pit Of The Seasonal Frozen Soil Area Based On Triaxial Shear Test Of Unsaturated Soil

Seasonal frozen soil is widely distributed,and the soil in this area is generally not satiety.Because of the particularity of soil and the temporary of the supporting structure,the frost heaving of the soil is not considered correctly in the design of the deep foundation pit in the non saturated soil of the frozen area,which causes the frequent accidents of the deep foundation pit engineering in the winter.Therefore,this paper based on triaxial shear test of unsaturated soil,the numerical simulation analysis method,on the season frozen zone of unsaturated soils in deep foundation pit under the effect of frost heave damage mechanism of in-depth research,the main results are as follows:First,Research status of soil,unsaturated soil,frost heave and frost heave mechanism in seasonal frozen zone is summarized in detail,and the application status of deep foundation pit supporting structure in the frozen area is summarized in a comprehensive way.Second,Combined with the existing research results,the basic properties of unsaturated soil,the mechanism of frost heaving force,the factors affecting frost heaving force in unsaturated soil,the types and causes of frost heave damage in deep foundation pit are theoretically analyzed.Third,The results of laboratory tests show that: in the process of freezing,with lower temperature,increase the cohesion of soil,and increasing the growth rate gradually rise,internal friction angle decreases and the decrease amplitude was lowered after the first trend;After a frozen melting process,the cohesion and internal friction Angle of the soil decrease,and the strength decreases.Unsaturated soil strength index changes as the change of saturation(matrix suction),among them,to a certain degree of saturation(matrix suction)within the scope of cohesion increases with the reduction of saturation increase and increase amplitude decrease gradually,internal friction angle increases with the reduction of saturation slightly reduced and and gradually tends to stability.Fourth,The results of numerical simulation show that: compared with many constitutive models,mohr-coulomb Model has the most reasonable simulation results.Temperature(0? to-15? to 15?),the largest displacement of supporting pile,the horizontal force,anchor axial force,displacement of the ground settlement top surface uplift displacement of soil,the foundation pit uplift,increases with the decreasing of temperature,recovery decreases with temperature;Soil frost heave is affected by saturation(matrix suction).Freezing process(15? to-15?),the strength index changing with temperature(cohesion increases gradually,internal friction Angle decreases),horizontal displacement of retaining structure,the maximum axial force and horizontal force,anchor at the top of the foundation pit uplift displacement of soil,the foundation pit uplift the surface subsidence displacement showed a trend of increase with the decrease of the first.