Meitan xuebao (Apr 2024)
Technology system and application of “artificial pre-fracture layer” by high level whole layer blasting for pressure releasing to source prevention and control of rockburst
Abstract
Active pressure relief is an important measure for source controlling of rockburst in coal mines. The current active pressure relief prevention and control method, or using the arranging holes along the roadway of the mining face, or underground in-situ hydraulic fracturing technology, has some shortcomings such as limited pressure relief protection range and constrained by the progress of pressure relief operation. When a surface hydraulic fracturing prevention system is used, it has the advantages of a wide range long-term of pressure relief, but may have the problem of high early investment, etc. Therefore, adhering to the innovative strategic ideas for pressure relief to prevent and control rock burst, which is from the source, prevention and economic efficiency, it is imperative to propose a new type of regional pressure relief source prevention technology system that is easy to practice, significant in effect, and can be comprehensively promoted. This paper proposes a new pressure relief technology system for high level whole layer pre-blasting of overlying rock. To blast higher key layers that can generate dynamic loads, the innovative high level rock tunnels, high level drilling sites, and blasting drilling arrangements are used to evenly pre-crack high level entire hard rock layers in advance, thus forming an “artificial pre-fracture layer”. This method breaks through the general limit of long drilling distance, greatly improving the pressure relief height, range, and effect of rock blasting, and can form a high-level “artificial pre-fracture layer” that covers the entire working face area or even multiple working faces before mining. The “artificial pre-fracture layer” of high level blasting first significantly weakens the weighting distance and weighting strength of the high level hard rock layer. Secondly, it also cushions and weakens the mining pressure transmitted downwards by the hard rock layer above it. Finally, it can also reduce the weighting step of the hard rock layer below it. After conducting the first “artificial pre-fracture layer” technology test for high level blasting pressure relief of overlying rock at the 3409 working face of Tingnan coal mine, the on-site measurement results show that compared to conventional blasting pressure relief areas, the average pressure strength, pressure step distance, pressure duration distance, and pressure alarm frequency of the support are significantly reduced using this method. The stress in both deep and shallow holes of the roadway is also reduced. The total energy of microseismic events and high-energy microseismic events have significantly decreased, and the intensity has significantly decreased. Microseismic events in the middle section of the working face are particularly sparse. The burst risk area obtained from seismic source CT and the high energy AE events has also been reduced, and various actual measurement methods have verified the superiority of the artificial pre-fracture layer pressure relief prevention technology for high-level blasting.
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