Identification and on-site application of the main hazard-causing stratum of overlying strata in coal mines
In response to the challenging task of accurately identifying the main hazard-causing layer of overlying strata in the coal mine surface hydraulic fracturing construction,this study focuses on the industrial test of ground hydraulic frac-turing at the 401102 working face of the Mengcun Coal Mine.The research is conducted using the methods of theoretical analysis,microseismic monitoring,and on-site investigation to reveal the dynamic disaster mechanism of mine earth-quakes and rock bursts induced by the movement of thick and hard overlying strata in the coal mines.The relationship between the movement characteristics of thick and hard overlying strata based on a three-zone structure loading model of overlying strata and induced dynamic disasters is analyzed,and a prediction model for mining seismic energy and an es-timation model for equivalent additional stress in mining areas based on the movement state of key layers are established.A coal mine identification technology for the main hazard-causing layer of overlying strata is proposed based on the K-means clustering algorithm and the elbow rule.The construction layer for hydraulic fracturing is determined,and an indus-trial test is carried out on-site.The effectiveness is verified based on the microseismic monitoring data and theoretical ana-lysis results,leading to the following conclusions.In the Mengcun Coal Mine's 401102 working face,both the key strat-um responsible for rock bursts and mine seismic activities can be traced to the R9 key stratum of the Anding Group,situ-ated 66 meters away from the coal seam.The primary fracturing movement of this critical stratum R9 imparts an equival-ent supplementary disturbance stress value of 7.23 MPa,with the seismic energy liberated by this initial rupture motion quantifying to 6.08×105 J,thereby indicating a pronounced susceptibility towards catastrophic occurrences.After fractur-ing the key layer which induces mining earthquakes and rock bursts,the theoretical value of the mine earthquake energy is reduced by 94%,and the theoretical value of the equivalent disturbance stress of the working face is reduced by 76%.High-energy microseismic events above the working face with an energy of 5×103 J show a noticeable upward trend,with an up-ward movement of approximately 15 m.The frequency ratio of microseismic events with an energy level of 103 J or high-er significantly decreases from 60.39%to 17.89%,and the maximum microseismic event energy decreases from 6.65×105 J to 9.75×103 J.The proportion of microseismic events with an energy level of 102 J and below significantly increases from 39.61%to 82.11%.
surface hydraulic fracturingrock burstmine earthquakeoverburden main control hazard-causing layeridentification method
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