| Red clay is a commonly used soil material for engineering construction and is one of the typical subgrade soils in southern China.However,the intrusion of heavy metal pollution elements into the soil results in damage to the microscopic mineral structure and deterioration of macroscopic mechanical properties,which seriously affects the engineering performance of the soil.To achieve the efficient utilization of subgrade red clay,this study aims to explore the mechanism of mechanical performance attenuation of cadmiumcontaminated red clay subgrade.Taking the red clay subgrade in Guilin as the research object,cadmium-contaminated red clay samples with different curing ages and cadmium ion concentrations were prepared.The effects of confining pressure,cadmium ion concentration,and curing age on the stress-strain relationship curve,shear strength and its indicators,unconfined compressive strength,and microstructure of cadmium-contaminated red clay were studied by triaxial compression test,unconfined compressive strength test,scanning electron microscopy test,and dry shrinkage cracking test.The study revealed the microinfluence mechanism of the change in macroscopic mechanical properties of cadmiumcontaminated red clay and proposed solidification measures for heavy metal-polluted red clay subgrade.The main research contents and conclusions are as follows:(1)Based on triaxial compression tests,the influence of confining pressure,cadmium ion concentration,and curing age on the stress-strain curves,shear strength,and related parameters of cadmium-contaminated red clay was studied.The results showed that the stress-strain curves of cadmium-contaminated red clay under different confining pressures,cadmium ion concentrations,and curing ages were strain-hardening.With the increase of confining pressure,the shear strength of cadmium-contaminated red clay showed a linear increase.With the increase of cadmium ion concentration,the shear strength and cohesion of low curing age cadmium-contaminated red clay increased,while they decreased for medium to high curing ages.The internal friction angle of cadmium-contaminated red clay with different curing ages showed a fluctuating increase trend.With the increase of curing age,the shear strength and cohesion of low concentration cadmium-contaminated red clay showed an increasing trend,while they showed a decreasing trend for medium to high concentrations.The internal friction angle of cadmium-contaminated red clay with different concentrations showed an increasing trend.(2)Based on unconfined compression strength tests,the influence of cadmium ion concentration and curing age on the unconfined compression strength of cadmiumcontaminated red clay was studied.The results showed that with the increase of cadmium ion concentration,the unconfined compression strength of cadmium-contaminated red clay had a tendency to decrease first and then increase after 7 days of curing age,while it had a tendency to increase first and then decrease after 14,28,and 56 days of curing age.With the increase of curing age,the unconfined compression strength of red clay contaminated by different concentrations of cadmium had a tendency to increase first and then decrease.(3)Based on scanning electron microscope tests and drying shrinkage cracking tests,the microstructural characteristics of cadmium-contaminated red clay were analyzed.The results show that the erosion effect of cadmium ions leads to the appearance of many unstable contact points and debris in the red clay.With the increase of cadmium ion concentration,the number of pores and cracks in the soil increases.With the increase of curing age,the cracks and pores in the soil continue to develop,the number of debris particles and flaky structure monomers increases,and a large number of fragmented block particles adhere to the surface of the unit body,and the microstructure of the soil changes significantly.In the process of water loss shrinkage,the red clay has fewer cracks and shows unidirectional expansion without through cracks,and the overall integrity of the soil is good.The cadmiumcontaminated red clay has a large number of cracks that expand in multiple directions,and the cracks basically penetrate the entire surface of the soil sample,leading to severe damage to the overall integrity of the soil. |
