Mesostructural alteration in porosity of iron tailings sand under freeze-thaw cycle studied by X-ray microcomputed tomography.

After experiencing periodic freeze-thaw cycles, the mesostructure of tailings sand in the tailings pond in seasonal frozen regions deteriorates, which directly threatens the safe and stable operation of the tailings pond. In order to reveal the alterations law of the mesostructure of iron tailings sand under the action of freeze-thaw cycles, the pore structure of iron tailings sand was characterized based on industrial X-ray microtomography technology. The response and variation trends of the pore structure of tailings sand to the moisture content and the number of freeze-thaw cycles were analyzed. A numerical model considering the irregular characteristics of particles was established to explore the dynamic process of the mechanical response among tailings sand particles under the action of freeze-thaw cycles. The results show that: the freeze-thaw effect leads to a decrease in the friction angle among tailings sand particles and an increase in the number of particles with an orientation angle of 45 °. The influence of moisture content on the throat diameter and pore coordination number is greater than that of the number of freeze-thaw cycles. There is a dynamic balance between the connection of small pores and the splitting and disintegration of large pores under different numbers of freeze-thaw cycles. During the freezing process of pore water in tailings sand, the particles in the specimen expand from the center to the periphery, and a force chain discontinuity area appears in the center of the model. Moreover, the area of the force chain discontinuity region is affected by the moisture content and the number of freeze-thaw cycles. A higher moisture content results in a larger pore expansion rate, fewer inter-particle contacts and a greater volume expansion. The research results of this paper can provide a reference for the safe and stable operation of tailings dams in seasonal frozen regions, and also support the establishment of the strength deterioration mechanism of tailings sand at the mesoscale under the action of freeze-thaw and the analysis of its influencing factors.