Influence Of Different Dry Density On Deformation And Strength Of Unsaturated Soil

In this thesis,the silty clay of the bottom of a foundation pit engineering in Wuhan is taken as the research object,based on unsaturated soil mechanics mainly on the performance of non saturated soil water characteristic curve changes and mechanical conditions of different initial dry density through the TSZ-2 type automatic three axis instrument,GDS unsaturated soil three axis instrument and pressure plate instrument,The main research contents are as follows:(1)The soil water characteristic curve of unsaturated soil under different initial dry density was obtained by pressure plate test and the parameters of the mathematical model are obtained,through the analysis of model parameters we can know that :The larger the dry density is,the larger the inlet value is,the more uniform pore size distribution,the slope of soil water characteristic curve becomes smaller after inflection point,and the water holding capacity of the specimen can be seen from the slope of the soil water characteristic curve by that the smaller the slope,the better the water holding capacity.The water stability of samples increased with the increase of dry density.(2)By using Van Genuchten,Fredlund and &Xing,Gardner three kinds of soil water characteristic curve model fit to find that in addition to the dry density of 1.5g/cm~3,1.6g/cm~3,Gardner,R2 of the model was 0.94 and 0.949,the values of other correlation coefficient are more than 0.96,and the fitting effect is good.When the author analyzed the 3 model parameters in Gardner,Van Genuchten model found that there was a good correlation between them and dry density,Therefore,a simplified method for determining the model parameters by the dry density is obtained to avoid the complex testing process for obtaining the model parameters,which was certain practicality,expected to provide reference for the project.(3)Analysis of stress-strain curves of soil samples tested by the TSZ-2 type automatic three axis instrument and GDS unsaturated soil three axis instrument,we can find that:The stress-strain curves of remolded unsaturated soils are characterized by strain hardening and the stress-strain relationship is in accordance with the hyperbolic model.With the increase of the dry density of samples,the hardening tendency of stress and strain curves decreases,and the initial tangent elastic modulus increases with the increase of matrix suction.The strength of unsaturated silty clay with the same dry density increases with the increase of suction.With the increase of suction,the contribution of matrix suction to the shear strength decreases.The volume change of samples with different dry density decreases with the increase of suction,and the larger the dry density is,the closer the samples volume change are.(4)Processing the experimental data obtained from the three axis test and when the axial strain is 15%,the axial stress is the failure stress,the failure stress((q_f,p_f))depicted in the p-q plane,the effective internal angel?cohesion and cohesion force of the sample can be obtained by linear fitting and calculation and the variation of them with suction was analyzed.(5)Processing the experimental data obtained from the three axis test by Duncan-Chang model and the tangent deformation modulus and volume deformation modulus were been analyzed.This paper enriches the understanding of unsaturated soil water characteristic curve,the deepening of the unsaturated soil strength and deformation of understanding,which was certain practicality,expected to provide reference for the project.