| The coal resource is abundant in our country,and many of them are hard roof coal seam.There is a serious threat of hard roof mining safety production,especially in the initial mining period,the roof integrity is good,which will not collapse in the short term.Thus,the first weighting step is very large,causing large roof caving and gas emission in goaf,which is easily lead to roof and gas accidents,damage to equipment and even casualties.Therefore,take measures to make hard roof caving in advance,so as to avoid the roof accidents and the occurrence of gas accidents has been highly valued.In this paper,the deep-hole blasting technology is used to crack the hard roof in advance,and the basic theory of deep-hole blasting rock breaking is discussed.The rock burst fissure expansion and the initial collapse of the roof were simulated and analyzed respectively by ANSYS / LS-DYNA and UDEC.Based on the working face of 3404 fully mechanized coal caving face in Dayang Coal Mine,the blasting scheme is designed and implemented,and the effect of the initial pressure of the roof and gas control of the fully mechanized top coal caving mining face in the initial mining period by the method of deep hole blasting prefabricated roof is analyzed.The main conclusions are as follows:(1)The related parameters of rock blasting are determined.The theoreticalcalculation shows that the radius of the crushing zone is 38.5cm and the radius of the fracture zone is 195 cm.Using the ANSYS / LS-DYNA3 D software,the numerical simulation is carried out.The radius of the crushing zone is about39.5cm and the radius of the fissure zone is about 185 cm.The numerical simulation results are basically the same as the theoretical results.(2)Deep hole blasting makes the roof from the fixed beam structure into the cantilever beam structure,so that the first step of the roof reduce the step distance;Using the UDEC numerical software,the initial collapse step of the roof under pre-splitting condition and non-pre-cracking condition is simulated,the results show that the initial collapse step of the top coal is reduced by 6.0m,the initial collapse step is reduced by 9.6m,and the initial step of the main roof is reduced by 12.0m.(3)The same borehole was observed before and after blasting,the results show that before blasting,the borehole wall is more complete,and there are many cracks in the borehole wall after blasting.(4)The field test shows that the initial collapse step and the initial pressure step of the top coal caving in the 3404 fully mechanized top-coal caving face are 8m and 10 m respectively,compared with the 3303 working face without the pre-splitting measures.The initial dynamic load of the stent during the initial pressure to the minimum 1.03,the largest 1.26,an average of 1.10.It is indicated that the stope support is safe when the roof is pre-cracked.(5)Deep hole pre-splitting blasting can effectively prevent gas overrun during working period.Pre-mining on the roof before the burst of pre-crack,so that the original cracks in coal and rock body expansion,and produce many new cracks,undermining the integrity of the roof,significantly reduced the initial collapse of the top coal and the old roof of the initial pressure step,andreduce the roof area of the mined-out area,so that the top auxiliary air return lane in advance to play a role in favor of the face ventilation management,reducing the face and the upper corner of the gas concentration to ensure that the initial mining work during the safe production.(6)The measurement of the concentration and the amount of gas in the high borehole borehole is measured and analyzed.The results show that the pre-cracked roof is fractured with the roof movement,and the roof rock is fractured in advance,leading to a large amount of gas to be drilled out of the upper hole.It is one of the reasons for the decrease of the gas concentration at the working face and the upper corner during the initial mining period. |
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