Abstract: The characteristics and precursory law of rock burst in roadway are different when the coal-rock composite bearing structure is under different stress boundary conditions. The true triaxial loading and single face unloading test is performed on coal-rock combination bodies under high static and dynamic load, using high frequency vibration acquisition and borehole imaging triaxial static and dynamic load experimental system. The mechanical characteristics and strength conditions at the interface of coal and rock mass are analyzed. Failure modes, dynamic characteristics and evolution of acoustic emission signals of coal-rock combination bodies under different stress boundaries are investigated. The results show that: 1)the strength of sandstone at the interface is "weakened" due to the mutual restriction of coal and rock deformation. When the stress at the crack tip of the coal body at the interface is greater than the strength of the "weakened" sandstone, the crack will develop into the sandstone through the coal rock interface, and the sandstone presents the failure form of buckling spalling and splitting into plates. 2) Under high static loading, the deformation and failure characteristics of coal-rock combination bodies and the acoustic emission signal have obvious precursory law. Before the bearing failure of coal-rock combination bodies, the local particle ejection kinetic energy of coal body increases, the particle lumpiness decreases, and the acoustic emission signal changes from "high frequency and low energy" to "high frequency and high energy". The failure mode of coal-rock mass is mainly shear-tension composite failure. 3) Under the impact dynamic loading, the loading effect of sandstone on the top and bottom plates is weakened, the stress at the crack tip of the coal body can not be effectively accumulated, and the crack is blocked when it extends to the coal rock interface. The combination is dominated by the tensile failure of coal samples, and the acoustic emission signal shows the characteristics of "high frequency and high energy", but it is mostly concentrated after the impact failure, resulting in the dynamic failure of the combination, which is difficult to predict. 4) Compared with static loading alone, although the static load level is low under the superposition of dynamic and static loading test, the ejection quality and fractal dimension of ejection fragments of coal rock assemblage are large, and the average particle size of broken fragments is small. Dynamic load plays a positive role in the failure of coal-rock combination mass while static load provides stress and energy conditions for the dynamic failure of coal-rock combination mass.

Key words: mining engineering, rock burst, dynamic and static coupled loading, coal-rock combined samples, dynamic characteristics, premonitory information law