Rockburst prevention mechanism and effect test of blast presplitting of hard roof in gob-side roadway

Roof blast presplitting technology is an important means to preventing rockburst. Taking the frequent occurrence of rockburst in the gob-side roadway with hard roof in Ordos as background, the mechanical and UDEC numerical models of gob-side roadway overburden structure are established. The characteristics of overlying rock structure and stress evolution before and after roof presplitting blasting are compared. The rockburst prevention mechanism of blast presplitting in gob-side roadway is revealed. The practice of preventing rockburst with blasting is carried out. The lateral overburden structure and coal stress in gob-side roadway before and after blasting are measured by means of drilling exploration, peeping, stress monitoring, and microseismic. The following conclusions are drawn: ① roof presplitting blasting can promote the structural transformation of long-arm “F” → long-arm “L” → short-arm “L” type of the lateral overburden, shorten the cantilever length of key layer, reduce the static load stress of coal seam, promote the peak stress of coal seam to transfer to the deep, and weaken the dynamic load of lateral overburden, reduce the risk of rockburst. ② Before and after blasting, the measured fracture angle of lower rock stratum increases from 57° to 72°, and the cantilever length decreases by 8.7 m, while the cantilever length of the middle-high level key layer decreases by at least 6.8 m. The pre-splitting blasting of lower rock stratum induces the fracture of middle-high level key stratum, confirming the transformation of overlying rock structure in gob-side. ③ Before and after blasting, the numerical calculation shows that the peak stress reduction of the coal in gob-side is 5.36 MPa, and the measured maximum stress reduction of coal seam is 5.4 MPa, the energy and frequency of microseismic events are significantly reduced, the measured and theoretical results are consistent. ④ A method for testing the rockburst prevention effect of blasting by combining multiple means such as borehole exploration, peeping, stress and microseismic monitoring has been formed.