Effect of early damage on the mechanical properties, localized deformation and damage failure of cemented tailings backfill

To investigate the effect of early damage on the mechanical properties of cemented tailings backfill (CTB) in the later stage, different degrees of stress damage were applied to CTB at different curing age. Unconfined compressive strength (UCS) and ultrasonic testing were conducted on CTB. The acoustic emission (AE) and digital speckle correlation methods were used to analyze the AE response characteristics and localized deformation patterns of CTB. The results show that when the damage age (DA) is short and the damage degree (DD) is low, a smaller compressive stress can improve the internal density of CTB and enhance its UCS and wave velocity. A high compressive stress has a deteriorating effect on the UCS and wave velocity of CTB. When DA is 14 d, the amount of hydration products generated inside the CTB has decreased, and it is not enough to fill the cracks caused by stress damage, reducing the UCS and wave velocity of the CTB. An increase in DD can enhance the elastic modulus of CTB at various curing age. As DD increases, the failure mode of CTB transitions from shear failure to splitting tensile failure and then to composite failure via shear and splitting tensile failure. The AE counts and energy peak values of CTB increase continuously with increasing DD. When the DD is 40%, 60%, or 80%, there is a significant sudden increase in the AE count and energy near the peak stress point, which can be used as a precursor to CTB instability and failure.