Mechanism and application of force-structure cooperative prevention andcontrol on rockburst with deep hole roof pre-blasting

Based on the analysis of deep hole roof pre-blasting, the mechanism of force-structure cooperative prevention and control of rockburst using deep hole roof pre-blasting and its types were put forword. Mises equivalent stress field, plastic failure area and the change law of effective stress and displacement of typical material points under different bole hole arrangements were simulated and the field rockburst prevention and control was carried out. The research shows that the deep hole roof pre-blasting can damage the roof by the strong impact of dynamic load, the action of impact air wedge of high temperature, high pressure and high speed detonation gas and the rebound tensile action of heat exchange. Therefore, it reduces the energy storage capacity of the internal structural unit of rock mass, and promotes the crack through and the weak fracture surface formed. Under the action of mine pressure, the roof can break along the predetermined position, which can weaken the mechanical properties of roof rock and optimize the fracture structure of rock. Compared with the linear and three pattern bole hole arrangements, the deep shallow combination makes the effective stress of Mises more sufficient in the scope and time of action, and increases the probability of blasting fracture density and multi-directional development. Also, it prolongs the time of the blasting attenuation energy acting on the rock, and makes the plastic failure area more developed and the blasting fragmentation more even. When the working face enters into or out the roof breaking area, the movement of overlying strata is not coordinated and the stress/energy transfer is not continuous, thus it is easy to induce the impact ground pressure. When the phenomenon of “lack-earthquake” appears in the micro-seismic monitoring of roof blasting area, it can be used as a typical prediction precursor for rockburst.