Study On The Predictive Method Of Coal And Gas Outburst With The Large Diameter Borehole In Front Of Working Face

Coal and gas outburst prediction is divided into regional prediction and faceprediction in China.At present，the Φ42mmdrilling is widespread used in coal and gasoutbursting prediction.The benefit of coal and gas outbursting prediction with Φ42mmdrilling is safe and reliable,however its deficiency is low efficiency.The situation isespecially serious for PingDingShan mine area.In reaction to this phenomenon,thispaper has done a lot of research on large diameter Φ89mm drilling outstandingprediction method in coal roadway’s heading face of PingDingShan mine area.This paper puts the eighth coal mine of PingMei group company as the testsite,analyze the coal and gas outburst characteristics and the influence factors,get thegas content and pressure at the beginning by gas depth at the beginning.and give supportto establishing a sensitive index and a relationship between gas content and thepressure;It analyses the inner relationship between coal and gas outburst mechanism andprediction index, puts forward the index Q₃which reflects the characteristics of coalseam gas initial desorption, confirms preliminary outstanding forecasting index of Largediameter bore Q₃、△h₂、drilling cuttings quantity S according to the main controllingfactors of the outburst in study area; the coal sample drilling cuttings gas recorery indexin study area is determined by simulation in the laboratory.At the same time,therelationship between every desorption index and the gas content and pressure has beenanalysed. The test results and the field test all show that drilling cuttings gas desorptionindex Q₃reflects initial desorption volume features better after coal seam dischargingpressure.The Q₃is suitable to be as the predictor for work.Its critical point can bedetermined by gas pressure and gas content. We perliminarily got a part of criticaltheory prediction indexes based on the combination of the laboratory and field research;Using the principal component analysis method, we determined to make the Q₃and S asface outburst dangerous prediction sensitive index in large diameter drilling conditions.We make sure the sensitivity index critical point of large diameter bored outstandingprediction by laboratory research combined with field tracing and observation and threerate method in the8th mine: drilling cuttings gas recorery index Q₃（the F and the Ecoal seam gas drilling cuttings desorption index Q₃critical value respectively are 31ml/100g and35ml/100g）,drilling cuttings quantity S（the F and the E coal seamdrilling cuttings quantity S critical value is9Kg/m）. According to the certain sensitiveindex and its critical value, we make the industrial test application, and the results showthat outstanding predictor is sensitive; critical value is reliable. Large diameter boredoutstanding forecast system is preliminarily set up.