Effect of different rock strength on the uniaxial compression bearing characteristics of rock-backfill body-rock combination

In order to study the impact of roof and floor rock mass strength on the overall mechanical properties of rock and backfill body，the uniaxial compression tests were conducted on the rock-backfill body-rock combination under conditions of both uniform and different strengths of the roof and floor. The study focused on the failure modes，stress-strain curves，uniaxial compression strengths，and acoustic emission characteristics of different combinations under uniaxial compression conditions. The results show that when the strength of the backfill body is lower than that of the roof and floor rocks，the failure of the combination is primarily caused by the instability of the backfill body. When the strengths of the roof and floor rock are low，splitting damage occurs in both the roof rock and the backfill body. As the strength of roof and floor rocks increases，the backfill body exhibits obvious shear damage while the ends of the rock remain relatively intact. When the strength of the roof and floor rock are identical，the elastic modulus and peak strength of the combination tend to increase with the increase of rock strength. Conversely，when the strengths of the roof and floor rocks are different，the elastic modulus and peak strength of the combination initially increase and then decrease as the strength of the floor rock increases under the condition that the strength of roof rock remains constant. In contrast，when the floor rock strength is held constant，both of them show an increasing trend with the increase of the roof rock strength. The rock- backfill body-rock combination exhibits an obvious acoustic emission response during the loading process，with the acoustic emission ringing count of the combination at the peak strength continuously increases with the increase of rock strength. The cumulative ringing count curve of the specimens presents a trend of rapid growth-stable growth-rapid growth. The energy migration instability model of the combination under different roof and floor conditions is developed，which reveals the energy accumulation and distribution law of the combination during the loading process. These findings provide theoretical insights for understanding the collaborative bearing mechanical characteristics of the roof and floor rocks and backfill body under the condition of constructional backfill mining.