Study On The Inrush Mechanism Of The Water In Bed Separation Due To Repeated Coal Mining Under Hard Rock

Water inrush threats the coal safe production in China. Recently, because of the raise of the production of the coal, the raise of the mining depth and the multi-seam mining, a new type of the roof water disaster, the water in roof bedding separation inrush appears. It has characters of large instantaneous water quantity, no obvious Symptoms of the water inrush and great harmfulness, which receives more concerns in recent years. At present, the research work focuses on the formation mechanism of the bed separation, distribution regularity and the engineering applications of subsidence reduction with grouting in the bed separation. Few research work has been done on the formation conditions and the inrush mechanism of the water in bed separationBy theory analysis, field tests, experiments in the lab, numerical simulation and application in practice, for the purport of the description the inrush mechanism of the water in bed separation in Haizi Colliery, this thesis deeply studies the formation and inrush mechanism of the water in bed separation under the hard overburden due to repeated mining. The study work is centering on the formation of the bed separation, the formation of the water in bed separation and the inrush of the water in bed separation, based on analyzing the background conditions the inrush disaster of the water in bed separation. the key control technology of the water in bed separation is presented, which has been used in practice. The following results are obtained.(1)With surface drilling, the well logging of the injection flow, borehole televiewer and discrete element method simulation, the development rule of the bed separation in Coal 7 overburden is studied due to the Coal 10 and Coal 7 repeated mining. The natural state of the Coal 7 overburden damaged after the mining of the 1049 work face. The bed separation in the thick sandstone occurs at the bottom of the igneous rock. The bed separation expands due to the repeated mining of the 745 work face. The thick sandstone is the aquifer, which promotes the accumulation of the water in bed separation by supply the water. The other bed separation is located in the aquifuge and becomes the vacuum bed separation.(2)The 4 basic conditions of the formation the water in bed separation are presented. The first, the bed separation is above the water flowing fractured zone. The second, the recharge water source is around the bed separation. The third, the bed separation sustains long enough. The last, the surrounding rock has high permeability.(3)To study the unloading influence on the rock permeability, the man-made fractured rock samples permeability tests are done with unloading the confining pressure to failure. Used random fracture network model by Monte-Carlo method, the numerical simulation is done to study the fixed stress ratio, variable stress ratio. The results show that the permeability of sandstone is big enough to accumulate much water in bed separation in some time. It is important. Used discrete element method, the permeability REV is decided as 8m. The mathematical model of the water flow in thick sandstone aquifer injection into the bed separation is obtained by describing the permeability of the water in sandstone with equivalent continuum theory.(4)Whether the inrush of the water in bed separation occurs is judged by the water inrush coefficient method. Based on excess hydrostatic pressure test’s results, the water inrush coefficient of the water in bed separation loaded by the igneous rock impact is calculated. If the calculated value is higher than the critical water inrush coefficient, the water inrush must occur.(5)The impact damage effect of the igneous rock sudden failure is studied by similar model test and discrete element method. The results show that if the igneous rock sudden failure occurs, its impact shock effect causes the horizontal and vertical stress of the strata under the thick sandstone bed separation higher than the capacity strength, and the high deformation velocity occurs. The horizontal and vertical deformation increases continuously, which cause the sudden failure and connects with the lower water flowing fractured zone. The inrush channel of the 5.21 Water Inrush Disaster forms.(6)Using elastic theory, wave mechanics and elastic stress wave theory, theoretical derivation on the dynamic process of the igneous rock sudden failure damaging the lower strata is done. The calculation formula of the dynamic breakthrough zone is presented.(7)The engineering geological model of the water in bed separation under the hard overburden is proposed, which points that the accumulation of the water in bed separation is the critical reason of the inrush disaster of the water in bed separation. Based on the research results, the control technology of the water in bed separation is presented, which contains using the water closure and diversion borehole of the water in bed separation to truncate the recharge the water in bed separation and advance dewatering the water in bed separation. The technology was used in the resumption production of the 745 workface of Haizi Colliery, which insures safety and high effective product.The thesis has 79 figures, 22 tables and 262 references.