基于双向聚能拉张爆破理论的巷道顶板定向预裂

为在切顶卸压沿空留巷中获得巷道顶板预裂炮孔的最优间距，基于双向聚能拉张爆破技术，采用以LS-DYNA动力分析软件为基础的数值模拟和现场试验对巷道顶板定向预裂进行研究，优化炮孔间距。数值模拟结果表明，当炮孔间距为400 mm时，应力波叠加后产生有效的拉应力；当炮孔间距为500 mm时，应力波叠加后也能够产生有效的拉应力，该拉应力大于孔壁围岩的抗拉强度，能够使孔壁围岩沿聚能方向形成裂缝，且利于炮孔间裂纹的扩展；随着炮孔间距进一步的增大，当炮孔间距为600 mm爆破时，由于间距过大，应力波无法有效叠加，不能产生连续裂缝。现场试验表明，间距为400和500 mm的炮孔间隔爆破时，未爆破孔自炮孔孔底至孔口产生连续有效裂缝，裂缝长度达2.4 m，相邻炮孔间沿炮孔中心线均能够形成连续有效的切缝面，能够有效控制沿空巷道顶底板位移及沿空巷道顶板压力。综合分析，在3种不同炮孔间距的试验方案中，确定间隔爆破、500 mm的炮孔间距为同一地质条件下3种试验设计中的最优方案。

Directional pre-splitting of roadway roof based on the theory of bilateral cumulative tensile explosion

To obtain the optimal pre-splitting hole spacing in a retained gob-side entry formed by roof cutting and pressure releasing, we investigated the directional pre-splitting of the roadway roof under bilateral cumulative tensile explosion using the LS-DYNA software and field test. The numerical results showed that the effective tension stress was generated after the stress wave superposition when the hole spacing was 400 mm; that when the hole spacing was 500 mm, the effective tension stress was also higher than the tensile strength of the hole wall rock, thus forming the cracks in the hole wall rock along the direction of cumulative energy and expanding the cracks between the adjacent holes; and that when the hole spacing was 600 mm, the cracks between the adjacent holes failed to form because the hole spacing was too large to generate the effective tension stress. The field tests showed that continuous cracks were formed from the hole bottom to porthole in the blasting-free holes when the hole spacing was 400 or 500 mm and the crack length reached 2. 4 m, forming a continuous cutting surface and effectively restraining the displacement of roof and floor and the roof pressure along the roadway in the gob-side entry. Out study concluded that the interval blasting with a 500 mm hole spacing was the optimal design in the three tests under different hole-spacing conditions.