Shear behavior of ultrafine magnetite tailings subjected to freeze-thaw cycles

To study the shear behavior of the ultrafine magnetite tailings subjected to freeze-thaw cycles,unconsolidated-undrained shear tests were conducted on ultrafine-grained tailings that were subjected to 1–11 cycles of freeze-thaw and defined as a type of clayey silt under confining pressures of 100, 200,and 300 kPa. Taking the number of freeze-thaw cycles, cooling temperature, initial dry density, and moisture content as the four main influencing factors of shear behavior of the tailings samples, the shear stress-strain curve, compression modulus, failure strength, cohesion, and internal friction angle were measured. The results show that the freeze-thaw cycle has an obvious weakening effect on the shear behavior of the tailings material, and the shear mechanical parameters are affected by a combination of confining pressure, freeze-thaw cycle condition, and initial physical-mechanical properties of the tailings samples. Through the microstructural analysis of the tailings samples subjected to freeze-thaw cycles, it shows that the freeze-thaw cycle mainly affects the porosity, bound water, and arrangement of the tailings particles. Subsequently, the macroscopic changes in shear strength indexes emerge, and then the stability of the tailings dam will decrease.