Study on mechanical properties and energy damage evolution of cemented tailings backfill under the coupled effect of immersion curing temperature and age

The backfill mining method is now in the transition stage from shallow to deep, and cemented tailings backfill (CTB) is subjected to the coupled of water and high temperature in the deep environment. Based on indoor tests and the theory of energy conservation, this paper investigates the mechanical properties and energy damage mechanism of CTB after water immersion at different temperatures (20, 35 and 50 °C) and ages (3, 7, 14 and 28 days). The results showed that the increase of both the curing temperature and age were beneficial to the mechanical properties of CTB, the water-weakening effect affected the deformation process of CTB, and the peak strain (PS) of CTB increased with the increase of the curing temperature and decreased with the increase of the curing age. The energy difference (e_k) curves of CTB under different curing conditions can be divided into four stages and correspond to the stress-strain curves. The weakening effect of water affects the rate of energy exchange of CTB, and the increase of curing temperature and age will enhance the energy absorption and transfer performance of CTB. The weakening effect of water slows down the rate of development of the slowly rising phase and the steadily rising phase of the dissipative energy curve, which is facilitated by the increase of the curing temperature, while the increase of the curing age leads to the rapid development of CTB dissipative energy curve in the rapidly rising phase. At lower curing temperatures and ages, the surface cracks of CTB were not prominent, and the “soft damage” effect was obvious. With the increase of temperatures and ages, the failure mode of CTB changed from shear damage to mixed tensile-shear damage. In this study, CTB with a solid content of 75% and a tailings-to-Portland cement ratio of 10:1 were prepared and subjected to immersion curing at 20, 35 and 50 °C for periods of 3, 7, 14, and 28 days. Following the curing process, unconfined compressive strength (UCS) tests and Brazilian splitting tensile strength tests were conducted at a constant loading rate of 0.5 mm/min.