Study On The Mechanism And Monitoring And Early Warning Technology Of Strong Pressure Behavior In Close Multi-seams Mining

Due to the special occurrence conditions of coal and rock and repeated mining disturbance,the mechanism of strong pressure behavior induced by dynamic and static load superposition is complex,which brings new challenges to mine safety production and monitoring and early warning of strong pressure behavior.It is urgent to study the mechanism of dynamic and static load and establish applicable monitoring and early warning methods.Therefore,the paper comprehensively uses the methods of field investigation,theoretical analysis,numerical simulation and engineering practice to carry out the research on the mechanism of strong pressure behavior and monitoring and early warning technology of close distance coal seams.The main achievements are as follows:(1)Taking Xinzhouyao coal mine as an example,the characteristics and main influencing factors of strong pressure behavior in close distance coal seams were studied.The strong pressure behavior of the lower coal seam mining is greatly affected by the overlying coal pillars and goaf.The strong pressure behavior is mainly located in the gob-side roadway under the overlying coal pillars,and it is more serious at the intersection of the overlying irregular coal pillars.The large energy mine earthquake is mainly concentrated in the upper coal seam,and presents the zoning characteristics highly related to the location of the overlying coal pillars.Because most of the large energy mine earthquakes are far away from the mining space of the lower coal seam,the lower coal seam is less affected by the far-field dynamic load disturbance,and the strong pressure behavior is mainly manifested as the two sides approaching,floor heave and roof subsidence,without large rockburst.(2)The multi-source static load mechanical model of the gob-side roadway under the overlying coal pillar is established,and the contribution degree of each static load force source to the stress concentration is obtained.The example calculation shows that the overlying coal pillar above the gob-side roadway is the main factor leading to stress concentration,the overlying coal pillar above the gob-side roadway transfers 78.3%of the stress,the lateral abutment pressure transfers 16%of the stress,and the peak stress is 1.8 times of the original self weight stress.The theoretical criterion of far-field dynamic load induced by mining of lower coal seam is constructed.When the damage range of floor caused by mining of upper coal seam and that of roof caused by mining of lower coal seam are connected,the mining of lower coal seam is easy to induce the secondary instability of overlying rock and the destruction of remaining coal pillar,and produce far-field large energy dynamic load disturbance.(3)The study reveals the comprehensive action mechanism of regional dynamic load and local static load in the mining of close distance coal seams,and establishes the criterion of regional dynamic load local static load comprehensive induced strong pressure behavior considering the attenuation of seismic wave.The results show that the propagation of vibration wave accords with exponential attenuation under the condition of no mining.The goaf and interlayer plastic zone of close distance coal seam group will aggravate the attenuation of vibration wave,and with the increase of the scope and damage degree of interlayer plastic zone,the greater the influence on the attenuation of vibration wave;the main factors causing the strong pressure behavior of the lower coal seam gob-side roadway are multi-source static load stress concentration and near-field dynamic load disturbance,Because the dynamic load occurred in the upper coal seam roof or the overlying coal pillar area is far away from the mining space of the lower coal seam,and at the same time,it passes through the goaf and plastic failure area,so the disturbance damage to the mining space is small.The distance from the dynamic load to the mining space is an important factor to induce the strong ground pressure behavior of the short distance coal seam group caused by the superposition of dynamic and static loads.(4)Microseismic events are highly related to the spatial overburden structure of close coal seams.Before the high-energy microseismic events,the mean value of microseismic frequency and the mean value of microseismic sliding have an obvious downward trend and then upward trend.Electromagnetic radiation and support stress can reflect local stress concentration.Based on this,the MS frequency ratio,weighted center position and dispersion index for predicting the occurrence time and location of regional dynamic load.The electromagnetic radiation amplitude,pulse number overrun amplitude and support stress overrun range index are constructed to monitor the danger degree of local static load stress concentration.Based on the weighted center position of microseisms and the attenuation law of dynamic load,the calculation method of local influence weight of dynamic load is established.Based on the criterion of regional dynamic load local static load comprehensive induced strong ground pressure behavior considering seismic wave attenuation,the regional local integrated early warning method of strong pressure behavior in close distance coal seams group is established.The above results are applied and verified in Xinzhouyao mine.The results show that microseismic frequency ratio,dispersion and weighted center position index can be used for real-time early warning and spatial position prediction of large energy microseisms.The results of regional local integrated early warning are highly consistent with the records of roadway deformation and damage and the results of seismic wave CT detection.The reliability of the prediction is verified by the records of roadway deformation and rockburst failure and the detection results of passive velocity tomography.