Experimental investigation on the deformation and strength properties of cemented gangue backfill column under long-term axial compression

To reveal the time-dependent deformation and the effect of loading history from early curing age on mechanical properties of cemented gangue backfill column (CGBC) under long-term axial compression in constructional backfill mining, the step-by-step load was adopted to simulate the loading history of the roof before 28d and then enter the long-term creeping stage, and the uniaxial compressive strength and elastic modulus of samples after 360d loading were tested. Four initial loading ages (ILA) and four stress-strength ratios (SSR) were set to simulate the actual loading conditions. The time-dependent damage process of CGBC was monitored by ultrasonic and electrical resistivity equipment. The results show that: the strain of CGBC increases with the increase of loading time and SSR; the earlier the ILA is, the higher the total strain shows, but the smaller the creep strain after 28d will be. The loading history at early curing age increases the compactness of CGBC and promotes the cement hydration process, and decreases the deformation after 28d. The final strength and elastic modulus of the long-term loading samples are larger than those of the control ones, and increase first and then decrease with SSR 60% and ILA 7d as the turning point, and the most increase reaches 33% and 82%, respectively. The CGBC can keep long-term stability at 80% SSR. The competition of compaction, healing and damage of CGBC under different SSRs at early curing age determines the final mechanical properties. Ultrasonic pulse velocity and resistivity of CGBC increase with the increase of time and are also affected by the SSR. A rheology-based model that considered the time-hardening of CGBC at early curing age was proposed to predict the time-dependent defor-mation of CGBC starting from early age. The results could be used to guide the design of CGBC and deformation prediction of the roof.