Abstract: Rockburst must occur under the drive of energy. In this study, a mechanical model of coal-rock combined body was constructed to explore the accumulation layer of energy causing rockburst in coal-rock system, and a formula of pre-peak energy distribution of coal-rock combined body was deduced. The experiments of energy accumulation under five loading rates of fine sandstone-coal (FC), coarse sandstone-coal (GC) and fine sandstone-coal-coarse sandstone (FCG) were carried out. The failure characteristics, mechanical properties and energy accumulation law of the combined body were analyzed. The results showed that: 1) At a loading rate of 0.001 mm/s, the pre-peak energy of the combined body was mainly dissipated slowly in the form of primary crack propagation and coalescence, which belongs to complete plastic failure; and at the 0.1 mm/s loading rate, the pre-peak energy of the combined body was mainly released rapidly in the form of local ejection failure, which belongs to brittle incomplete failure. 2) The compressive strength, elastic modulus, pre-peak energy and impact energy index of the combined body have a logarithmic relationship with the loading rate. As the loading rate increases, the increases of compressive strength, elastic modulus and impact energy index decrease gradually, and the pre-peak energy growth rate shows a "low-high-low" trend. 3) The energy storage and energy share of coal components increase as the loading rate increases. At the 0.001−0.010 mm/s loading rate, the accumulated energy of coal components increases rapidly and at the 0.010－0.100 mm/s loading rate, the accumulated energy of coal components increases slowly. 4) At the same loading rate, the energy proportion of coal components is in the following order: FC combined body > FCG combined body > GC combined body. 5) The energy proportion of coal component in the combined body surpasses 50%, and the coal component is the main carrier of energy accumulation. Under the same stress condition, the energy accumulation ability of weak rock is stronger than that of hard rock. In other words, energy is more easily accumulated in weak rocks. The research results can provide an insight into determining the energy accumulation layer of rock burst and the work of energy release and impact reduction.

Key words: rock burst, coal-rock combined body, loading rate, mechanical properties, pre-peak energy, energy accumulation