Strength degradation mechanism analysis of cadmium-contaminated laterite
In this study,we revealed the strength degradation mechanism of cadmium-contaminated laterite to investigate how cadmium-contaminated laterite microstructure evolution influences the shear strength of the soil.We studied the shear and microstructure characteristics of cadmium-contaminated laterite using direct shear tests,X-ray diffraction(XRD)analysis,and scanning electron microscopy.Our results demonstrated the following:Cohesion decreased by 25.5%and the internal friction angle increased by 21.1%on average with the increasing cadmium content.Therefore,the shear strength tended to deteriorate,and the shear failure surface shapes became more evident.The microstructure of cadmium-contaminated laterite underwent significant restructuration with the particle erosion phenomenon,coupled with pore development and honeycomb formation based on the microscopic image analysis.Honeycombed pore development increased by 11.8%on average.The soil particle contact modes changed from the angle-side,edge-side,face-face to angle-side,and point-face.The microstructure indices(particle abundance,orientation frequency,and pore fractal dimension)reflected the change soil particle characteristics from strong to weak contact.Due to the strong adsorption capacity of clay particles to cadmium ions,the diffusion electrical double layer was compressed and hydrolysis occurred between the cadmium ions and carbonates in the clay.Therefore,the binding force of the water film between the clay particles was reduced and the cohesive structural function gradually weakened.In summary,cadmium contamination exerts a deterioration effect on laterite shear strength to worsen soil erosion in the cultivated land layer under the surface runoff effect easily.
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