Dynamic impact performance of cemented tailings backfill in a water-bearing environment: Coupling effects and damage characteristics

Cemented tailings backfill (CTB) is a way to make full use of tailings, but its dynamic mechanical and damage characteristics under water bearing environment are still not clear. In this paper, CTB was completely immersed with different immersion time (5 d, 10 d, 20 d, 30 d) under different initial immersion age (3 d, 7 d, 14 d, 28 d). The dynamic compression test under different impact velocity (3.0 m s⁻¹, 4.5 m s⁻¹, 6.0 m s⁻¹, 7.5 m s⁻¹) was carried out by using split Hopkinson pressure bar. The mechanical properties and damage evolution law of CTB were analyzed by low field nuclear magnetic resonance and SEM. Results show that the post-peak stage characteristics of the stress-strain curve of water-immersed CTB under impact load is divided into four types, which are type I “strain rebound”, type II “stress drop”, type III “post-peak plasticity”, and type IV “post-peak ductility”. Water immersion effect mainly increases the peak damage degree of CTB and the proportion of the damage before the peak strain to the total damage. Under impact load, water immersion effect reduces the bearing capacity of the gel matrix of CTB and promotes the dislocation of tailings and the expansion of the original crack surface. However, the free water in the pores do not have enough time to flow to the tip of the original crack, which hinders the crack growth. Based on Weibull distribution and Kelvin model, the dynamic aging damage model of water-immersed CTB is constructed, which provides a theoretical basis for analyzing the failure mechanism of CTB under water immersion. Besides, it is suggested that reducing the immersion time of CTB in water is the key factor to improve the stability of CTB.