临空留巷底板冲击地压启动区判定与分步防治技术

以山西余吾煤业N2105工作面回采过程中临空留巷底板冲击地压为工程背景,理论分析底板冲击地压可能的冲击启动区及主导应力源,采用数值模拟追踪煤层开挖后侧向煤柱及留巷围岩各向应力、位移的演化过程,建立采空区影响下留巷底板水平应力演化模型并进行验证。基于临空留巷底板冲击地压主导力源判定及能量传递过程分析,提出该类底板冲击地压分步防治关键技术,并进行现场应用。结果表明:煤层开挖后中,临空留巷底板在破坏深度范围内存在"卸压通道"机制,临空煤柱垂直应力不断增长的同时,留巷底板水平应力通过"卸压通道"释放,释放程度与该通道宽度呈正相关。临空煤柱帮内弹性核区为留巷底板冲击地压的冲击启动区,其不断增长的垂直应力为主导载荷源,而非留巷底板水平应力。为阻止该类底板冲击地压发生启动,关键在于削弱采空区侧向顶板压力传递作用及煤柱弹性能积聚水平,弱化留巷底板只能缓和冲击显现强度,非对称支护对留巷围岩变形破坏特征的适应性更强。

Determination on start-up area for floor rockburst at retained entry and its stepwise control technology

Entry floor usually suffers the greatest damage after floor rockburst.But the start-up area is not neces-sarily located within the floor.Based on the floor rockburst occurred at retained entry behind working face in a coal mine in Shanxi Province,the time and space sequences of rock burst associated with their corresponding relationship were analyzed,and then the possible start-up area was pointed out.Numerical simulation code FLAC was utilized to analyze the load evolution law for the retained entry,and the “relief channel” model within the floor was established.Based on field data,the key parameters for stepwise control technology for rockburst were determined,and on-site applications was carried out.The results showed that:“relief channel” mechanism occurred within retained entry floor among the range of failure depth after the lateral coal was mined-out.The vertical stress in pillar increased,while the horizontal stress in the retained entry floor released through “relief channel”.And the decline extent was positively correlated with the channel width.The elastic core area within pillar was start-up area for floor rockburst,and its increasing vertical stress was the leading load source.Due to the low strength of the floor,it became the main area where vibration energy transformed to the crack surface energy and kinetic energy.In order to prevent start-up and mitigate the extent of damage of rockburst,the stepwise control technology was utilized,including the advanced pre-split within the hard roof,drilling within start-up area,setting drilling within cache corner to buffer shock,and non-asymmetric support at retained entry.After the application of technology above,the rock burst was successfully contained.