Effect Of Freeze-thaw On Strength Index Of Unsaturated Soil And Overwintering Of Excavations

In recent years,due to the large amount of engineering construction and long construction period,overwintering excavations inevitably exists in seasonal frozen soil area.The shear strength index of unsaturated soil varies greatly in the process of freezing and thawing,and the soil in seasonal frozen soil area is generally unsaturated.excavations overwintering is greatly affected by frost heave and thaw settlement of soil.Therefore,triaxial tests are carried out on unsaturated soil during freeze-thaw process.Based on the parameters obtained from the tests,numerical simulation is used to simulate the overwintering excavations under freeze-thaw action.The main research results are as follows:1.The research history and current situation of unsaturated soil,Frost Heave Mechanism and the effect of freeze-thaw on supporting structure at home and abroad are summarized in detail.Combining with existing theories,the generation of frost heave and frost heave force and the mechanical deformation of excavations supporting structure under freeze-thaw action are analyzed theoretically.2.The soil-water characteristic curve of silty clay in Changchun area is obtained by using GDS unsaturated soil triaxial apparatus.The data obtained are fitted by two mathematical fitting models,and the fitting function and curve are given.The results are of great significance to the study of mechanical properties,shear strength and permeability coefficient of unsaturated silty clay in this area.3.A triaxial test of unsaturated soil under a certain matrix suction is carried out to obtain the strength parameters of soil at room temperature,freezing and after freezing-thawing.The results show that the cohesion and internal friction angle of frozen soil are higher than those of normal temperature soil,and the increase ofcohesion is large,and the internal friction angle is slightly higher;the cohesion and internal friction angle of frozen and thawed soil are lower than those of normal temperature soil,and the decrease of cohesion is large,and the internal friction angle is slightly lower.4.Based on the soil parameters obtained from the tests under different conditions,the numerical simulation analysis of overwintering excavations is carried out.The variation of deformation and horizontal frost heave force of excavations in winter is studied.The results show that the numerical simulation of soil parameters varying with temperature is closer to the actual freeze-thaw process of excavations.