地下洞室爆破开挖诱发围岩损伤特性及PPV阈值研究

地下洞室爆破开挖产生的围岩损伤主要由爆破荷载和地应力重分布共同作用引起。针对圆形隧洞全断面毫秒延迟爆破开挖过程，采用LS-DYNA有限元数值模拟研究了不同地应力水平下爆破开挖诱发围岩损伤的机理及爆破损伤PPV阈值变化规律。研究表明，地应力对爆破荷载产生的张拉损伤起抑制作用，高地应力条件下，爆破荷载产生的岩体损伤仅限于围岩表层，地应力重分布引起的岩体压剪破坏是围岩中大范围损伤区形成的主要原因；爆破过程中开挖面上地应力瞬态释放所产生的附加动应力也是影响围岩损伤的重要因素，相比于准静态卸荷，地应力瞬态卸荷产生的围岩损伤范围更大；随着地应力水平的提高，岩体爆破损伤的PPV阈值呈先增大后减小的变化趋势，地下洞室爆破安全振动控制标准应考虑地应力状态的影响。
Abstract：When underground openings are excavated with the drill and blast method,the rock damage surrounding openings is induced mainly by the combined effects of blast loading and in situ stress redistribution.For a circular tunnel excavated with the full-face millisecond delay blasting method,a numerical model was established to investigate the mechanism of rock damage under different stress levels.The PPV thresholds for the initiation of blast damage were also studied.The numerical studies were performed by using the finite element software LS-DYNA.The results show that the tensile failure of rock caused by blast loading is suppressed by in situ stresses.When the in situ stress reaches a higher level,the blast-induced damage is distributed only in the immediate vicinity of tunnel walls.The stress redistribution can cause a wider damage zone on the tunnel profile in a compression-shear mode.The additional dynamic stress that arises from the transient stress release on blast-created excavation surfaces is another important factor affecting the behavior of rock damages.Compared with the quasi-static stress redistribution,the transient stress release generates a larger damage zone.With the increase of the in situ stress levels,the PPV thresholds for the initiation of blast damage first increase and then decrease.Therefore,under underground blasting excavation,the influence of in situ stress on blast damage should be considered in the safety control standards of blasting vibrations.