Research On The Strength And Deformation Characteristics Of Modified Expansive Soil In Southern Shaanxi By NaCl Solution

Expansive soil is more common and widely distributed in other areas in southern Shaanxi,China.Due to its unique characteristics such as absorption of water expansion,loss of water shrinkage and attenuation of immersion capacity.It is imperative to solve the problems of engineering construction,disaster prevention and mitigation,and reinforcement and repair work in the expansive soil areas.It also causes severe economic losses.Therefore,it is necessary to improve and modify the expansive soil in different areas so that it can reduce the adverse impact on the actual process of the project and meet its construction requirements.At present,there are more and more engineering projects related to the construction and landslide management in the South Shaanxi expansive soil area.Relatively little research has been done on the area's expansive soil modification,so that it is of great practical significance to study the influence of Na Cl solution on the expansion of South Shaanxi expansive soil on its expansion characteristics,strength and deformation characteristics and microstructure characteristics.It provides theoretical and experimental basis for further research and application in engineering practice in the area.In this paper,the expansive soil in the Mianxian area of Hanzhong in southern Shaanxi is taken as the research object.It analyzes the basic physical properties,shear strength indexes,deformation and microstructural changes of expansive soils under Na Cl solution modification conditions.The main research contents are as follows:?1?XRD mineral composition analysis of expansive soil samples through routine laboratory tests.It also can measure a series of basic physical property index parameters such as natural density,gravity,natural moisture content,limit moisture content and free expansion rate of soil samples.In addition,the Na Cl solution with a degree of use of 0.1mol/L,0.5mol/L and1mol/L interacted with the expansive soil and observed the change of its swellability parameters.It was initially judged that the Na Cl solution had an inhibitory effect on swellability and was feasible.The results show that both the boundary moisture content and the plasticity index of the modified expansive soil have a significant downward trend.With the increase of Na Cl solution concentration,the degree of decline is greater.At the same time,the free expansion rate of the expansive soil also decreased.The expansion type of the expansive soil was reduced from medium expansive soil to weak expansive soil under the action of Na Cl solution.?2?Aiming at expansive soils modified with different concentrations of Na Cl solution,conventional triaxial compression and shear tests were performed under different consolidation confining pressures and sample moisture content conditions.It Investigates Na Cl solution concentration,consolidation confining pressure,and sample moisture content about the effect of the shear strength and strength index of expansive soil.According to the test results,the shear strength and limit moisture content of the expansive soil are positively related to the consolidation confining pressure,and negatively related to the sample moisture content and the Na Cl solution concentration.And the influence on internal friction angle is weak.?3?The effects of consolidation confining pressure,sample moisture content,and Na Cl solution concentration on the stress-strain relationship curve of expansive soil in triaxial compression-shear tests are studied.It can be seen that the stress-strain relationship curve is ideal under low confining pressure Elastic molding.Under high confining pressure conditions,they are mostly strain hardened.Secondly,under the conditions of low concentration and low sample moisture content,the stress-strain relationship curve of the sample is mostly strain hardening or ideal elastic-plastic type.And as the concentration of the modified solution and the sample moisture content increase,the stress-strain curve gradually shows the tendency of strain softening.?4?Analyze the change law of the strength and deformation of the expansive soil in southern Shaanxi and explore its influencing mechanism.Increasing the confining pressure increases the restraining force in the directions of?₂and?₃of the sample,which makes the internal particle arrangement of the soil more and more compact,and the soil skeleton more rigid.Improve the effective stress of the soil sample and control the change of the moisture content during the test.This results in a strain-hardening stress-strain curve and improves the ability of the soil to resist shear failure.The increase of water content makes the content of weakly bound water and free water between soil particles increase,and the thickness of water film between particles increases,leading to a decrease in internal friction angle.At the same time,the connection between particles is weakened,and the cohesion of expansive soil is reduced.As the concentration of Na Cl solution increases,the thickness and net repulsion of the electric double layer of the expansive soil particles decrease,and the ability to prevent displacement between the particles decreases.The mineral components in the soil react,the content of cementing materials decreases,and the mutual embedding and mechanical interlocking between the particles of the expansive soil are weakened.Therefore,the cohesion and internal friction angle of the expansive soil are reduced to varying degrees.?5?The XRD electron microscope scanning instrument was used to study and analyze the influence of sample moisture content and modification solution concentration on the microstructure of expansive soil.As the water content increases,there are fewer inter-particle pore areas in the microstructure of the expansive soil.The microstructure is mainly composed of flake-shaped,flat particles through face-to-face contact.With the increase of Na Cl solution concentration,the number of inter-particle pores increased slightly.The composition of the microstructure is changed to granular and block-like,face-edge and edge-edge contact forms.In order to explain the internal causes of macroscopic phenomena,the microstructure of the expansive soil in southern Shaanxi is explained.