Research on the mechanical properties and acoustic emission characteristics of coal-based solid waste backfilling body with special layered structure

The backfilling process of initial gangue throwing followed by grouting with backfilling slurry solved the long-standing engineering problem of insufficient slurry transport distance. However, it resulted in the formation of a backfill body with a special layered structure in the goaf. Research on the mechanical properties of this layered backfill body is crucial for controlling overburden movement and environmental protection. In this study, orthogonal test methods were used to investigate the evolution of mechanical properties of layered backfilling body (LBB) with different preparation parameters. The significance of the four influencing factors was obtained by range analysis and variance analysis, and the macro- and micro-scale progressive failure process of LBB was revealed. The results show that the uniaxial compressive strength (UCS) of LBB at different ages is positively correlated with the mass concentration of backfilling slurry and gangue backfilling rate. The average UCS of LBB at the curing age of 3 d, 14 d, and 28 d is 0.56 MPa, 1.78 MPa, and 3.01 MPa, respectively. The peak acoustic emission (AE) ringing counts were 155, 128, and 235, and the peak energy values were 862, 383, and 1180 mV·ms for the low-, medium-, and high- UCS LBB, respectively. The upper layer of a LBB structure has weaker strength and is susceptible to the effects of inhomogeneous interfaces, which generates cracks from the upper layer and gradually expands to the lower layer, and eventually forms penetrating cracks and loses the load-bearing performance. It presents a theoretical basis for the parameter design of the backfilling project and the stability study of the LBB.