Abstract: Uniaxial cyclic loading and unloading experiments on pure coal, coal-rock assembly and pure rock specimens were designed and conducted to study the mechanical response and energy evolution law of coal-rock assembly under external load. The mechanical response characteristics such as uniaxial compressive strength and elastic modulus of test specimens were analyzed, and the evolution law of input energy density, elastic energy density and dissipated energy density of coal-rock assembly were examined in detail. The characteristics of elastic energy storage rate and energy storage capacity of different specimens were obtained, and the energy failure mechanism of coal-rock assembly were discussed. Results demonstrate that: 1) The mechanical parameters of coal-rock combined specimens are closer to those of pure coal specimens, mainly affected by the coal. 2) With the rise of external load, the input energy, elastic energy and dissipated energy of coal-rock combined specimen present obvious non-linear increase trends, in which the proportion of elastic energy is much higher than that of dissipated energy. 3) Under external load, elastic energy is stored in coal and rock masses synchronously; but as elastic energy reaches the storage limit in coal earlier than that in rock, the coal mass breaks and releases elastic energy to the rock mass. When the storage limit in rock mass is reached, failure of rock mass occurs.

Key words: coal-rock assembly, mechanical response, energy evolution, cyclic loading and unloading, energy storage