Deterioration characteristics of mechanical properties of heterogeneous accumulation of iron tailings sand under the action of freeze-thaw cycles

The heterogeneous accumulation structure of tailings sand poses a serious threat to the safe and stable operation of tailings ponds. However, analyses of how freeze-thaw cycles affect the mechanical properties of heterogeneous tailings-sand accumulations are limited. In this paper, based on triaxial compression tests and nuclear magnetic resonance tests, we analyze the macroscopic mechanical properties and mesoscopic pore evolution of the heterogeneous accumulation structure of tailings sand under the action of freeze-thaw cycles. Results show that as the number of freeze-thaw cycles rises, the shear strength of specimens with different interface inclination angles decreases significantly, and the magnitude of decrease correlates positively with the inclination angle. Under low confining pressure, the stress-strain curves of specimens with larger inclination angles exhibit strain softening. Under the action of freeze-thaw cycles, the deformation modes of coarse sand, fine sand, and specimens at various inclination angles can be categorized as shear dilation or a combination of shear dilation and contraction, with the failure mode being transverse fracture. Freeze-thaw cycles cause the “migration and accumulation” of pore water in tailings sand specimens. Interface structures of tailings sand accumulations with different particle sizes can significantly shorten the “migration and accumulation” period, presenting more intense phenomena of small pore connectivity and large pore collapse. Confining pressure strengthens tailings sand and can amplify freeze-thaw–induced strength deterioration. The filling of the lower-layer pore spaces by fine particles increases the interfacial strength of the tailings-sand at the interface. The small particles located above the interface act as weak structural planes and are more prone to deterioration. These findings provide both macroscopic and microscopic perspectives on how freeze-thaw cycles degrade the mechanical properties of sand and soil.