Research And Application Of Blasting Fracturing And Pressure Relief Technology For Thick And Hard Roof In Ⅱ7₂24N Working Face Of Renlou Coal Mine

Roof control and gas control have become the main factors restricting the safe mining of working face in close distance coal seam mining under thick sandstone.With the mining of the working face,a large area of thick and hard roof is suspended,so that the stress of the fully mechanized hydraulic support and the surrounding rock also increases with the exposed area,which will cause damage to the support structure of the fully mechanized mining face.At the same time,because of the lack of fracture development in the complete thick and hard roof,the gas in the goaf accumulates in the upper corner,causing accidents such as gas overrun.Aiming at the problems of strong strata behavior caused by thick and hard roof hanging and gas accumulation in upper corner which affect the safe mining of working face,the thick and hard roof of II7₂24N working face in Renlou coal mine is taken as the engineering background.The pressure relief mechanism of thick and hard roof caused by deep hole blasting and the technology of improving gas drainage effect are studied by combining theoretical analysis,similar simulation test,numerical simulation and field test of working face.The paper has carried out the following research work:According to the suspended state of thick and hard roof in the mining process of coal mining face,the mechanical analysis of the rock beam model of thick and hard roof is carried out to obtain the calculation formula of the initial and periodic weighting step of roof rock beam,and the fracture model of thick and hard roof is established.The formulas of the radius of the crushing ring and the radius of the fracture ring in the process of explosive explosion and the calculation formula of the propagation law of the blasting crack are deduced.The technology of blasting crack and pressure relief and improving the gas extraction effect of thick and hard roof is studied.The similar material ratio experiment was carried out,and the similar material ratio of different rock layers was obtained.A test platform is built in the laboratory to simulate the vertical stress environment,monitor the rock strain signal and detect the failure of model rock mass.The numerical simulation software was used to simulate the development of model stress and the expansion of cracks under blasting load.The test results show that the explosive stress wave produced by explosive blasting redistributes the rock mass stress around the blasting hole,produces blasting cracks,destroys the integrity of the thick and hard roof,cuts off the stress transfer path of the thick and hard roof,reduces the stress concentration degree of the coal seam,and plays a role in relieving the pressure of the coal seam and the rock layer,which can make the thick and hard roof from the non-caving roof to the caving roof.The vertical cracks generated after blasting extend downward from the upper part of the blast hole to the coal seam,which provides a channel for the vertical displacement of the gas,and also provides a path for the subsequent high-level drilling to extract gas through the roof cracks.The deep hole blasting cracking test was carried out on the thick and hard roof of II7₂24N working face in Renlou coal mine.The test results show that the support resistance of the working face is much lower than the rated resistance of the support,which avoids the occurrence of hydraulic support support crushing and achieves the purpose of pressure relief of thick and hard roof.With the help of the cracks in the roof,the high-level borehole gas extraction is carried out,and the extraction purity is increased and maintained at 6～8m³/min.The extraction concentration is increased and stabilized at about 35%,and the gas concentration in the upper corner of the working face is also reduced to below 1%,which ensures the normal advancement and safe mining of the working face.Figure 62 Table 12 Reference 87...