Experimental Study On The Shear Strength Characteristics Typical Unsaturated Silty Clay Of Shaoxing

In a large number of foundation pit projects,the soil above the groundwater level will be in unsaturated state due to seasonal change and rainwater evaporation.However,in the actual project,the stability analysis of foundation pit is still designed and calculated based on the shear strength index of saturated soil,which has a certain deviation from the actual project.Therefore,it is necessary to study the shear strength characteristics of unsaturated soil.The soil is affected by fluvial facies and marine deposits as a whole,and the geological conditions are very complicated in Shaoxing area.Among them,silty clay is a shallow surface soil,and most of it is often in an unsaturated state.In order to further explore the difference in soil stability between saturated and unsaturated conditions,and the influence of changes in initial dry density and initial water content on soil shear strength characteristics under different matric suction conditions.In this paper,the unsaturated soil consolidation instrument,unsaturated soil triaxial apparatus and unsaturated soil direct shear apparatus are used to study the typical unsaturated silty clay of Shaoxing area.The main research contents and achievements are as follows:(1)It is concluded that the test soil is a well graded low liquid limit silty clay by water content test,dry density test,boundary water content test,particle analysis test,specific gravity test and soil compaction test.(2)The unsaturated soil consolidation test is carried out on soils with different initial water content and different initial dry density through the unsaturated soil consolidation instrument,and the test results are fitted and analyzed with the VG model.The research results show that the greater the initial dry density,the greater the air entry value of the soil,the steeper the slope of the soil-water characteristic curve,and the weaker the water holding capacity;The greater the initial water content,the greater the air entry value of the soil,the slower the slope of the soil-water characteristic curve,and the stronger the water holding capacity.(3)Triaxial tests under different initial dry densities are carried out with the triaxial apparatus for unsaturated soil.The experimental results show that the shear strength,total cohesion,effective internal friction angle and adsorption internal friction angle of soil increase with the increase of initial dry density,and the stress-strain curve gradually transits from strain hardening type to strain softening type,and the greater the matric suction and net confining pressure are,the more obvious the transition effect is.With the increase of matric suction,the shear strength and total cohesion of the soil increase,the effective internal friction angle basically has no obvious change,and the adsorption internal friction angle gradually decreases.(4)Under the action of different initial water content and the suction of the matric are carried out constant suction direct shear test through the unsaturated soil direct shear apparatus.The test results show that with the increase of matric suction,the curve of shear stress versus shear displacement gradually transits from strain hardening type to strain softening type,and the shear strength characteristics of soil have no obvious change before air enter value,after the air enter value is exceeded,the growth rate of the total cohesive force first increases rapidly,then gradually slows down,the effective internal friction angle changes little,and the adsorption internal friction angle decreases rapidly until it stabilizes.With the increase of initial water content,the curve of shear stress and shear displacement gradually transits from strain softening type to strain hardening type.The total cohesion and effective internal friction angle increase first and then decrease,and reach the peak value at the optimal water content.(5)Based on three typical shear strength models of unsaturated soil,the shear strength of Shaoxing unsaturated silty clay is predicted,and an improved model formula is established to predict the shear strength of Shaoxing unsaturated silty clay under the action of different matric suction by comparing and analyzing the shear strength measured in the constant suction direct shear test.