Study On Mechanism Of In-Situ Stress Control On Floor Water Inrush During Deep Coal Seam Mining

It is imperative to mine deep coal resources along with the upper part coal seam dried up gradually in our country. The dangerousness and destructiveness of water inrush from coal seam floor is more and more serious in mining deep coal seam with the increasing depth of coal seam excavation. This is also intimate relationship with the high in-situ stress environment of deep coal seam roof and floor in addition to the reason of the increasing pressure of aquifer water under the coal seam floor. It is the key technology of safely mining deep coal resources that how to safely and effectively develop the deep coal resources from the condition of high geostress and high confined water pressure. We usually focus on water filling source, water filling way and water filling strength about shallow coal seam safely mining under water pressure. We didn’t focus too much attention to the control function and control mechanism of the ground stress size on coal seam floor water inrush in the working face, even we ignore them. But the original rock stress of surrounding rock increases rapidly with the increase of buried depth of coal seam. The mechanical properties of surrounding rock, the mechanical response characteristics after coal seam mining and the fracture mechanism of water inrush under high water pressure have different special properties from that of the shallow buried coal seam. The ground stress state becomes the important controlling factors of coal seam floor water-inrush. Therefore, from theory to engineering applications, it is the key scientific and technical problems to systematically study the inherent law of in-situ stress size and the buried depth of coal seam, to research the in-situ stress state of surrounding rock, the control mechanism of the high ground stress on mechanical property of coal seam surrounding rock, and damage characteristics of coal seam floor strata under the effect of mining disturbance and water pressurein high ground stress environment and its control effect coal seam floor water inrush, and then obtain the internal relation among the buried depth of coal seam, the size of the ground stress and hazard assessment index. That is the great demand of realizing safety mining deep coal seam under water pressure and in the deep high stress environment. It is based on the above reason, this paper chose the "Research on the control mechanism of the in-situ stress on deep mining coalseam floor water-inrush" as the main research contents and research direction.Mainly based on rock mechanics theory, the paper discussed the control effect of in-situ stress on the coal floor disturbance damage under the condition of different depth, and analyzed the control mechanism of in-situ stress on coal seam floor water-inrush. Author put forward the value relations with the in-situ stress and disturbance damage depth in coal floor. The paper obtained the rock strength, deformation characteristics, the change rule of permeability in full strain-stress process and the value relationship through triaxial compression test and permeability test under the condition of different rocks and confining pressure, and analyzed the control effect of confining pressure on the rock strength, deformation characteristics and penetration law. Author analyzed the change rule of water head loss in the process of high pressure water invading arise in water-resisting layer and the action mechanism of aquiclude charateristics on water head change through physical simulation experiment with water resistance performance of coal seam floor aquiclude, and studied the change feature of surrounding rock stress in mining coal, failure charateristics of plastic deformation and high water invasion development regularity based on Flac3D numerical simulation. And the calculation formula of water bursting coefficient is also revised. At the same time, the paper put forward evaluation and forecast method on water-inrush hazard degree in deep coal seam mining under water.This paper drew the following main conclusions through many research methods such as theoretical analysis, experiment research, numerical simulation and statistical analysis of the measured data and so on.1. Surrounding rock stress increases progressively with coal seam buried depth increasing. In-situ stress size is mainly proportional to the stratum depth.2. Floor water-resisting layer mining disturbance damage depth increases with increasing depth of coal seam. The size of the ground stress is basically proportional to the seam floor damage depth. The control effect of in-situ stress to floor damage depth is obvious.3. The ground stress size and progressive intrusion height has an increasing change rule. In-situ stress has certain action mechanism to progressive intrusion height of high pressure water intrusion damage.4. The paper put forward the concept of stress influence coefficient and its formula:Cd=0.1272Δσv+0.8066. And the existing water inrush coefficient formula was revised:Td=P/M·Cd. Meanwhile, author put forward evaluation and forecasting method (q-Td) on water inrush hazard degree in deep coal seam mining under water pressure.The research results are of important theoretical guiding significance and high practical value to to realize deep coal seam safe, orderly and efficient mining under the conditions of high geostress in the future.