Research On The Effect Of Deep-hole Presplitting Blasting In Low Oermeability And Extra Thick Coal Seam In Tingnan Coal Mine

For the coal mine with low permeability and high gas content like Tingnan coal mine,It is not effective to use the conventional method to extract coal seam gas,and it is difficult to relieve the gas threat during coal mining.It is an effective gas control method to strengthen the gas extraction of mining coal seam by deep hole pre-splitting blasting,which can improve the gas permeability of coal seam,and then realize the rapid gas extraction.Firstly,the pre-splitting blasting extraction scheme is designed according to the actual situation in the field,and the other parameters of pre-splitting blasting are given,except for the drilling spacing.After that,according to the coal seam deep hole pre-splitting blasting mechanism and the crack expansion mechanics model,the fractured expansion range is calculated through theoretical analysis and FLAC3D numerical simulation.The results show that the crack expansion range is about 3.4 m after deep hole pre-splitting blastingc,which provides the basis for the selection of drilling distance.By comparing single hole drainage radius values of field experimental and COMSOL simulation before pre-splitting blasting,the results agree with each other,so as to prove the simulation results of effective drainage radius is 3.6 m after pre-splitting blasting is reliability.Finally,considering the range of crack extension and the effective extraction radius,the reasonable hole spacing of the deep drilling pre-splitting blasting is 3.5 m.Through the observation of gas drainage for 3 months,the final results are obtained:The average single hole gas extraction quantity is 7 910.9 m3 after pre-splitting blasting,which is 2.36 times before the blasting.After the blasting,the gas extraction rate increased greatly,reaching 50.8%which satisfied the requirements of extraction and safe production.The permeability coefficient of coal seam was increased about 7.78 times,the average value is 2.607 m2/MPa2·d.The maximum amount of gas extraction by borehole is also increased to 9898.52 m3,it is about 5.27 times as large as that of the common.The anticipated effect of pre-splitting blasting is achieved and solves the problem of gas drainage in low permeability coal seam,provides reference and guidance for other mines with similar conditions.