Reasonable gas predrainage time at tunneling face

There are some problems on the tunneling face,such as gas predrainage time is not enough,drainage rate is low and the rate of burst out forecast is very high.By studing the attenuation law of the predrianaged gas,establishing the evaluation model of the reasonable drainage time for the tunneling face,the reasonable parameters are made out,thus the predrainage time of the gas is determined for Chengzhang Coal Mine,and inorder to test the result,experiments for drainaging in advance on the tunneling face are performed.The inspection result indicated that when the reasonsable drainge time is satisfy,the drainaging rate is enhanced,the remaining gas in the coal seam is reduced,and also the rate of burst out forecast exceeding the allowed figure is reduced;The evaluation model is reasonable and reliable,and the research of the reasonsable drainge time is valuable for the practical application.