Mechanical properties of cemented backfill under different unloading rates after cured at different temperatures

Abstract

In the process of deep filling mining in coal mine, due to the influence of mining and other factors, the confining pressure on both sides of cemented backfill decreases. It is necessary to master the mechanical characteristics of cemented backfill under unloading conditions in different temperature environments to ensure the stability of cemented backfill. To simulate the unloading process of cemented backfill in the deep highland environment of coal mine, triaxial unloading confining pressure tests of cemented coal gangue- fly ash backfill at different unloading rates after curing at different temperatures (20 ℃, 35 ℃ and 50 ℃) were carried out by the Rock Triaxial Testing System, and the mechanical characteristics of cemented backfill unloading were systematically studied. The findings of the study show that, for the same unloading rate, the peak strength of cemented backfill specimen reduces initially before increasing with curing temperature rises. After curing at the same temperature, the peak strength of cemented backfill specimen varies exponentially with an increase in unloading rate. The deformation modulus and volume strain at different unloading rates satisfy an exponential function relationship, while the generalized Poisson's ratio and volume strain satisfy a quadratic function relationship. Under unloading conditions, there was no large fracture or fragmentation of cemented backfill, only cracks appeared on surface. At the same unloading rate, cemented backfill specimen cured at 35 ℃ and 50 ℃ exhibits significantly more shear cracks after failure compared to the material cured at 20 ℃. As the unloading rate increases, the proportion of shear cracks generated during unloading failure of cemented backfill specimen cured at 35 ℃ and 50 ℃ gradually increases. In addition, the theoretical curve of the four-stage cemented backfill unloading constitutive model established in sections is essentially compatible with experimental curve, confirming the theoretical model's reasonableness. The study's findings provide a theoretical basis for evaluating stability of cemented backfill after unloading in deep high temperature (35–50 ℃) environments.