Study On Deformation And Shear Strength Characteristics Of Cadmium-contaminated Red Clay Under Dry-wet Cycle

Red clay is a kind of regional special clay,which is widely distributed throughout the country.Its high mechanical strength can be used as a good foundation soil.With the development of industrialization,the unreasonable discharge of heavy metal waste liquid caused heavy metal pollution in the surrounding soil,coupled with the repeated evaporation of nature in the rain,promoted the migration of heavy metal ions to the soil in all directions,affecting the soil structure and damaging the project Security construction.Therefore,it is of great theoretical and practical significance to study the changes in mechanical strength and microstructure of red clay contaminated by heavy metals under the action of dry and wet cycles.In this paper,the red clay in the Lijiang River Basin of Guilin,Guangxi is used as the research object.The Cadmium-contaminated Guilin red clay samples were prepared by artificially disposing different concentrations of CdCl₂ solution as a source of heavy metal pollution.The effects of Cadmium pollution and dry-wet cycle on the deformation,shear strength characteristics and microstructure of Guilin red clay were studied by using triaxial shear tests and microscopic scanning electron microscope tests combined with software processing image methods.The following conclusions were obtained:（1）By measuring the mass and volume of red clay during the dehumidification process in the wet-dry cycle,the change of water content,volume shrinkage,lateral and vertical shrinkage of red clay with time were studied.The results show that the moisture content decreases exponentially with time.Red clay samples with different concentrations of Cd²⁺have an initial volume expansion during the dehumidification process during the first dry-wet cycle,and then shrink to stable.The second and third cycles of dehumidification only caused shrinkage.（2）Based on the consolidated undrained triaxial shear test,the effects of Cadmium pollution and dry-wet cycling on the stress-strain relation curve of Guilin red clay were analyzed,and the shear strength of red clay under Cadmium pollution and dry-wet cycling conditions was explored Change law.The results show that under low confining pressure,the stress-strain relation curve of Cadmium-free red clay is ideally elastoplastic,and that of Cadmium contaminated red clay is strain-hardening.With the increase of confining pressure,Cadmium concentration and dry-wet cycle With the increase of the number of times,the degree of strain hardening of the soil is enhanced.The peak shear strength of red clay decreases exponentially with the increase of Cd²⁺concentration and increases with the increase of dry-wet cycling times.With the increase of Cadmium concentration,the cohesion of red clay decreased and the internal friction Angle increased.With the increase of the number of wet-dry cycles,the cohesion of the red clay without Cadmium pollution gradually decreases,the internal friction angle increases,and the red clay contaminates.The cohesive force first increased and then decreased,and the internal friction angle increased slightly.（3）The scanning electron microscope test was used to study the microstructure changes of Guilin red clay before and after Cd²⁺and dry-wet cycles.The results show that the action of Cd²⁺dissolves the cementitious substances inside the red clay,changes the connection between the units,and the increase of the porosity of the soil body weakens the mechanical strength on a macro scale,and as the concentration of Cd²⁺increases,The more significant changes in the microstructure of red clay;the dry-wet cycling effect caused the volume shrinkage of red clay samples,and microscopic tests showed that the spacing between soil particle units gradually decreased,and the macro-mechanical strength increased.