Rock Strata Failure Behavior of Deep Ordovician Limestone Aquifer and Multi-level Control Technology of Water Inrush Based on Microseismic Monitoring and Numerical Methods

The mining depth of most coal mines in North China has exceeded 1 km. The high seepage water pressure caused by high ground stress leads to the increasingly serious threat of water disaster in the mine. To explore the relationship and mechanism between water inrush from deep mining floor and grouting prevention, single-level grouting and multi-level cooperative grouting methods were carried out in Ordovician limestone confined aquifer of coal seam floor in Xingdong coal mine. Meanwhile, the temporal and spatial characteristics of rock fracture in the floor of deep mining face are revealed through the law of rock fracture microseismic. It is noteworthy that the occurrence time of water inrush and microseismic events have lag characteristics, that is, the occurrence time of microseismic events is earlier than that of water inrush. The multi-level cooperative grouting method can effectively control the non-uniform dissolution Ordovician limestone aquifer in-plane and vertical plane. Furthermore, single-level grouting and multi-level cooperative grouting methods are assumed to be unstable grouting and stable grouting. Besides, the flow pattern transformation characteristics of Ordovician limestone water in unstable to stable grouting are simulated by the finite element method. The results show that the energy inoculation level of fracture expansion around the aquifer decreases after stable grouting reinforcement. In other words, the multi-level cooperative grouting method can effectively strengthen and fill the water inrush channel and reduce the damage of high osmotic pressure to the aquiclude. It is of great significance to reduce the probability of water inrush in deep coal seam and ensure the mining safety of deep coal seam.