Mechanism and application of directional hydraulic fracturing roof cutting in hard roof
In order to promote roof caving in time and ensure safe production,the research on directional hydraulic fracturing roof cutting technology for hard roof was carried out in E9105 working face of Hengjin Coal Industry.According to the theory of fracture mechanics,the mechanical model of crack propagation under the combined action of ground stress and water pressure was established,and the for-mula for calculating the strength factors of type Ⅰ and type Ⅱ composite crack propagation were derived.Based on the maximum cir-cumferential tensile strain criterion,the crack initiation conditions and crack initiation rules were analyzed.The results show that when the original crack direction is parallel or perpendicular to the direction of σ1,the crack is self-similar manner.With the increase of water pressure,the cracking angle decreases gradually,and the crack is mainly type Ⅰ expansion.Combined with the geological conditions of the E9105 working face,the size of the water pressure was calculated,and the difference with the actual was small.The application of this technology significantly reduces the weighting interval and the working resistance of the support,which can provide reference for roof control under similar conditions.
hard roofdirectional hydraulic fracturingintensity factorcrack propagationcrack initiation angleworking resistanceweighting interval
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