Experimental Investigation of the Macromechanical Properties and Mesoscopic Structure of Iron Tailings Sand Improved by Clay under Dry–Wet Cycles

In order to investigate the deterioration characteristic of mechanical properties of iron tailings sand improved by clay under dry–wet (DW) cycles, conventional triaxial compression tests and scanning electron microscopy tests were conducted under different numbers of DW cycles to analyze the impact of DW cycles on the macroscopic mechanical properties and mesoscopic structure of the improved soil. The results showed that both the shear strength and the modulus of deformation of the improved soil decreases after DW cycles. The decrease is significant in the first cycle, followed by a gradual decrease in magnitude, and tends to stabilization after four cycles. The deterioration of cohesion is more significant than that of the internal friction angle. As the number of DW cycles increases, some of the clay particles in the improved soil are lost, some of the clay particles are attached to the iron tailings sand, and some of the clay particles form a regular shape within the agglomerates. This is evidenced by an increase in porosity of the improved soil, a change in the overall morphology of soil particles, and a transformation of micropores into mesopores and macropores. The loss of clay particles and the expansion of pores in the improved soil after DW cycles result in a nondense state, which is the fundamental cause of the reduction in shear strength and modulus of deformation of iron tailings sand improved by clay.