Experimental Study On Static And Dynamic Mechanical Properties Of Soil In Saline Sites

There are a large number of soil sites in northwest China.However,due to the special environmental conditions of arid and semi-arid in northwest China and the influence of concentrated rainfall,the water and salt movement in soil is intensified,resulting in a large amount of salt accumulation in soil sites,resulting in surface spallation,internal subsidence,collapse and other salt damage phenomena,which have a huge impact on the protection of soil sites.Therefore,this paper takes salt-bearing site soil with different proportions of Na2SO4 as the research object,and explores the mechanical properties of salt-bearing site soil through soil-water characteristic test,disintegration test,’lateral confined compression test,ring shear test and static and dynamic triaxial test,so as to provide reference and support for site protection and management.Specific research work and conclusions are as follows:(1)In order to explore the water properties of the saline site soil,soil-water characteristics tests were carried out on the reconstructed saline site soil with different contents of Na2SO4 and different dry densities.It was found that the water holding properties of the saline site soil were significantly affected by the content of Na2SO4 and dry density.Through disintegration tests,it is found that the water stability of the soil in the salt-bearing sites decreases with the increase of Na2SO4 content,and increases with the increase of dry density.Combined with the curve of disintegration amount and disintegration time,a fitting model considering the effect of salt content is established.(2)In order to explore the compression characteristics of the salt-bearing site soil,the lateral compression tests were carried out on the salt-bearing site soil with different Na2SO4 content and dry density,and the compression curve,compression coefficient and dissolution coefficient of the salt-bearing site soil were analyzed with the changes of the content of Na2SO4 and dry density.It was found that the compression coefficient and dissolution coefficient increased with the increase of the content of Na2SO4.In addition,hyperbolic function was used to fit the curves of the compression-subsidence relationship of soil samples at salt-bearing sites with different contents of Na2SO4,and the formula of the subsidence surface model was established based on different salt content and vertical stress.(3)In order to explore the influence of static strength characteristics of salt-bearing site soil,conventional triaxial shear tests were carried out on salt-bearing site soil with different contents of Na2SO4 and different dry densities.The effects of confining pressure,content of Na2SO4 and dry density on stress-strain relationship,p-q critical state line,cohesion c and internal friction Angle φwere analyzed.It is found that with the increase of the content of Na2SO4,the cohesion c and the internal friction Angle φ decrease first and then increase,and the limit salt content of the inflection point is 4%,while the increase of confining pressure and dry density will make the softening degree of the salt-bearing site soil gradually weaken.The parameters of Duncan-Zhang model were calculated based on the triaxial experimental data,and the variation law of Duncan-Zhang model parameters with the content of Na2SO4 and dry density was revealed.The effects of the content of Na2SO4 and the normal stress on the residual strength of the soil in the salt-bearing sites were studied by circumferential shear tests.It is found that the residual cohesion cr and the residual internal friction Angle φr decrease first and then increase with the increase of the content of Na2SO4.(4)In order to explore the dynamic strength characteristics of the soil at the salt site,the dynamic deformation tests of samples with different contents of Na2SO4,different confining pressures and different dry densities were carried out by a dynamic triaxial testing machine controlled by a microcomputer,and the dynamic characteristics of the soil at the salt site under the influence of various factors were revealed.It is found that under the same dynamic shear strain,with the increase of Na2SO4 content,the backbone curve and dynamic modulus first decrease and then increase,and the dynamic damping ratio first increases and then decreases.With the increase of dry density,the backbone curve and dynamic modulus increase,while the dynamic damping ratio decreases.With the increase of confining pressure,the shaft curve and dynamic modulus increase and the dynamic damping ratio decreases.