Abstract: In the constructural backfill mining, the composite bearing structure of 'backfill body-immediate roof' structure will be subjected to different loading rates depending on the mining speed and other conditions. According to the loading rate of 0.15− 2.40 mm/min, the uniaxial compression test of five groups of rock-backfill composite were carried out, and digital image correlation technology and acoustic emission monitoring were carried out to analyze the evolutionary characteristics of its energy loss. It can be seen from the experiment that the strength of siltstone is significantly greater than the strength of the rock-backfill composite and the backfill body, and the strength of the combination is closer to the strength of the filling body than the siltstone. It can be seen that 0.60 mm/min is the critical load for this group of experiments. When the loading rate of the rock-backfill composite is 0.15− 0.60 mm/min, the rock-backfill composite ultimately realizes the synergistic deformation of the siltstone and the backfill body in the rock-backfill composite and destruction of the rock-backfill composite in the process of loading, and when the loading rates are 1.20−2.40 mm/min, rock-backfill composite failed to achieve the collaborative deformation damage of the siltstone and the backfill body parts. When the loading rate is lower than 0.60 mm / min, due to the strength difference between the siltstone and the filling body and the non-uniform deformation of the contact interface between the two, a large crack penetrates the whole specimen. It can be seen that the final failure mode of each group of specimens is a tensile and shear mixed failure mode. By analyzing the dissipation energy changes of the rock-backfill composite and the backfill body, it can be seen that when the loading rate is greater than the critical loading rate, the pre-peak dissipation ratio of the rock-backfill composite is greater than that of the backfill body, and the composite can be destroyed in a coordinated manner. By calculating the energy storage coefficient and energy storage limit of the rock-backfill composite under different loading rates, it is found that when the loading rate is less than 0.60 mm/min, the higher the loading rate, the higher the energy storage limit of the combination specimen, and the speed of absorbing elastic energy is also rising synchronously. Finally, the backfill body part is destroyed first, and the energy released by the instantaneous damage is transmitted to the siltstone part of the rock-backfill composite, so that the elastic energy absorbed by the siltstone part can reach the energy storage limit. The crack in the backfill body part extends into the sandstone to achieve synergistic damage. The results of this study are intended to provide suggestions for ensuring the stability of the composite bearing structure of ' backfill body-immediate roof ' structure under different mining and filling rates.

Key words: rock-backfill composite structure, loading rate, collaborative deformation, evolution of energy consumption, constructional backfill mining