Mechanism Of Dynamic Disasters Induced By Super Thick Hard Strata Movement

The movement rule of super thick hard strata determines ground pressure behaviors in mining districts or longwall panels, especially in the these deep mines with dynamic disasters. Based on the mine pressure theory, overlying strata spatial structure theory, elastic-plastic mechanics and mine dynamic disaster theory, this dissertation studies the movement rule and instability mechanism of super thick hard strata, evolution characteristics of overlying strata spatial structure, mining stress development trend, occurrence mechanism and early warning mechanism of dynamic disasters, etc. through numerical modelling, geophysics(microseismic monitoring), real-time dynamic stress monitoring and ground subsidence measurement. The conclusions are as follows:During continuous mining, overlying strata are likely to form "O-S-O" shaped spatial structures under the control of super thick hard strata and horizontal stress transfer and concentration is the main cause of the instability of super thick hard strata.Taking the Tengdong Coal Mine as the research background, numerical modelling was used to simulate the plastic failure process of the super thick strata during mining, horizontal stress variation process in different mining phases and mining stress field distribution before and after the instability of the super thick hard strata. In the meantime, the rule of longwall panel stress swoop induced by the instability of the super thick rock strata was also analyzed. The mechanism of spontaneous rockburst and mine earthquake induced rockburst was analyzed according to the long panel stress distribution before and after the instability of the super thick strata.The monitoring and early warning system can be employed during mining in terms of the process and inducing-hazard mechanism of super thick hard strata instability. High-precision microseismic monitoring system was used to trace the strata fracture trajectory and analyze the spatial evolution process of the strata vibration field. Stress monitoring system was also used to analyze dynamic mining stress development tendency during the strata spatial structure evolution. In addition, ground subsidence and its velocity were analyzed by ground surface monitoring as well as its relationship with underground dynamic disasters. Thus, the monitoring of the development process of the dynamic disaster can be achieved as well as the objective of its phased specific prevention and control.Based on the characteristic that the instability of super thick strata causes longwall panel stress swoop, a kind of on-the-spot early warning method of mine earthquake induced rockburst was presented by analyzing the relationship between the stress swoop value and the swoop range. The key parameters of this early warning method were obtained by on-site application and this method fills up the gap in the field of on-the-spot early warning of rockburst.Stress conditions and failure conditions of the key rock masses of the super thick hard strata, it can be concluded that repeated mining leads to mining height increase and the external expansion of the overly strata movement line, and the instability of the super thick strata which are originally hinged and balanced, which thus reveals the mechanism of mine earthquake induced by caving and movement of the super thick strata during repeated mining.