Abstract: Sand-bearing rock is a special rock formed in the high-level key layer before water inrush and sand burst disaster. Its strength and mechanical properties are different from ordinary rock, which determines the stability of the high-level key layer. It is found that the fractured rock and sandy rock with different fracture angles have different characteristic stresses, and with the increase of fracture angle, the initiation stress, damage stress and peak stress of fractured rock and sandy rock increase, and the bimodal stress first increases and then decreases. The characteristic stresses of sandy rock under the same fracture angle are less than those of fractured rock, indicating that the sand body has a weakening effect on the characteristic stress of rock. From the perspective of failure form, the fractured rock is easy to show wing tensile fracture, the sandy rock is easy to form tensile fracture under the condition of low fracture angle (30º) and shear fracture under the condition of high fracture angle (60º), indicating that the sand body has shear effect on the rock after entering the rock fracture. At the same time, the mechanical model of sand filling is established, and it is pointed out that the reason why the strength of sandy rock is less than that of fractured rock is that the sand body reduces the friction coefficient of rock. Based on the cumulative acoustic emission ringing counts, the amount of rock damage is defined and the mechanism of sand-bearing rocks causing the disaster is analysed. The on-site sand-bursting disaster can be divided into four phases: 1) elastic deformation phase; 2) fracture expansion phase; 3) sand and energy storage phase; 4) sand-bursting energy release phase. Finally, PFC2D is used to verify the differences between fractured rocks and sandy rocks, and the energy evolution laws of different types of rocks are analyzed. The research results can be used as precursory information identification of water inrush and sand burst phenomenon in coal mine roof, and help to guide the safe production of water inrush and sand burst face.

Key words: acoustic emission, crack rock mass, characteristics stress, stress intensity factor