Evolution Laws of Cracks Under Different Hole Pitch in Deep Hole Pre-splitting Blasting

In order to research the influence of the distance from a control hole to a blasting hole on the evolution laws of fractures, finite element software LS-DYNA is used to carry out pre-splitting blasting of deep hole for different distance coal. It is concluded that under the effect of tensile stress superposition from stress wave and free surface reflection effect, blasting hole 3 m around the control hole can form 10 to 13 main cracks. And there is a long crack that even almost cuts through coal mass, and the stress strength on coal cutting edge is better than 4.5 m hole pitch. The hole spacing of 3 m is significantly increased than 4.5 m according to the comparation of the different from the data between extraction hole gas concentration and gas extraction pure amount within the scope of 3 m and 4.5 m. Hole spacing of 3 m is better than the other, and the pressure relief effect could be enhanced. The result proved that the effective pressure relief test area radius is 3 m to 4.5 m, which accords with the results of numerical simulation test.