Study On Rockburst Of Multi Fault Hard Roof Thick Coal Seam In Kilometer Deep Well

A mine in Jilin has complex geological characteristics such as mining depth of more than km,thick coal seam,hard roof and fault development.A rockburst accident occurred on June 9,2019 and production was resumed.However,there are many microseismic events in the daily production process,and high-energy microseismic events occur frequently,which is likely to happen again.Aiming at this problem,this paper takes the mine as the research object,analyzes the geological conditions of the mine,studies the mechanical properties and impact tendency of coal and rock in 513 working face of the mine,theoretically analyzes the disaster mechanism of rock burst in the mine,and introduces moment tensor to analyze the fracture type of microseismic events,Through the time-frequency analysis of microseismic signals,the waveform spectrum characteristics of typical roof fracture microseismic events,typical coal compression microseismic events and typical fault dislocation microseismic events in the mine are extracted,and then the temporal and spatial evolution law of microseismic events and the influence of mining activities on the activity of microseismic events are analyzed.Finally,according to the geological conditions and microseismic activity characteristics of the mine,the prevention measures are put forward,and the roadway support strength is calculated,The anti impact effect of the energy absorbing anti impact support is tested.The research shows that:(1)Due to the large mining depth of the mine,the vertical stress is large.According to the theoretical calculation,the vertical static load of 513 working face can reach 35MPa and the structural stress is 32.5MPa.Under the joint action of hard roof and fault,the coal seam is prone to instability and failure.It has the breeding conditions of roof fracture type rockburst,coal compression type rockburst and fault type rockburst.(2)The dominant frequency of typical roof fracture type microseismic events in the mine is10-30Hz,The dominant frequency of typical coal seam compression microseismic events is90-150Hz,The dominant frequency of typical fault dislocation microseismic events is 0-10Hz.Based on this,the nature of microseismic events can be identified by combining system positioning and moment tensor analysis of fracture types.(3)The microseismic activity of the mine is closely related to mining activities.The microseismic frequency and energy during mining stoppage are close to 0.During normal production,high-energy microseisms occur once every 8.6 days on average.Before the occurrence of high-energy microseisms,the total frequency of microseisms per day decreases,that is,it enters the quiet period.At the same time,the total energy released by microseismic events per day tends to decrease;After the occurrence of high-energy microseisms,the stress of coal and rock needs to be redistributed and adjusted.Therefore,the total frequency of microseisms every day increases,and the total energy released every day also increases.(4)The main fracture types of microseismic events in the mine are tension fracture and mixed fracture.Tension fracture and mixed fracture events account for 92.08%.Roof fracture and fault activity are the main dynamic load sources of microseismic events.Under the condition of large mining depth,the bearing pressure and tectonic stress exceed 30MPa,which are the main static load sources.They act together with the dynamic load generated by roof and fault under mining disturbance,resulting in the compression failure of thick coal seam.(5)The energy absorbing anti impact support has a good effect on improving the roadway support strength and resisting the rock burst.The calculation results show that the support strength of 305 working face can not resist the energy greater than Medium rockburst above 10~7J,while the support strength of 513 working face after installing energy absorbing anti impact support to strengthen the support is enough to resist the disastrous rockburst with energy greater than 10~8J.It shows that the energy absorbing anti impact support has obvious advantages compared with the traditional support means.