| The hard roof makes it difficult for the roof rock mass to collapse during the advancement of the coal mining face,which easily causes a large area of suspended roof behind the working face,thereby forming a higher support pressure,which is not conducive to the maintenance of the mining roadway.At the same time,the large-scale fracture of the hard roof collapsed,especially the sudden collapse of the large area of the hard roof,which brought the hidden danger of shock pressure to the normal production of the working face,which seriously affected the safety production of the working face.Therefore,in this paper,with the help of numerical simulation software,comprehensive application of theoretical analysis,field measurement,and other methods,the Yongning Coal Industry 31101 working face is used as the engineering background for the hydraulic fracturing pretreatment technology for the hard roof of the fully mechanized coal mining face in shallowly inclined and inclined coal seams The main research contents and results are as follows:(1)By analyzing the mining geological conditions of 31101 in Luning Coal Mine,including the conditions of the top and bottom of the working face,the support parameters of the working face,and the original rock stress,it is found that the 31101 working face has a large hardness problem,which is likely to cause a large area of hard The pressure phenomenon is not conducive to the safe and efficient production of the hard top working surface.(2)According to the analysis of the influencing factors of the stress arch at the working face of the 31101 working face,the mode of the roof rupture at the working face is summarized,which provides a basis for the design of the later hydraulic fracturing scheme.The FLAC3 D was used to simulate the mining stress field of the working face under the condition of the hard roof of the 31101 working face,and the vertical original rock stress of the stress field of the 31101 working face was analyzed to be 5.43 Mpa.Due to the advancement of the working face,the stress value in the surrounding rock mass before and after the work increases,and the increase is increasing.The stress concentration factor increases from 1.47 at 6m mining to 3.22 at 96m;the pressure relief within 10 m in front of the 31101 working face is pressure relief In the zone,the range of 10 ~ 68 m is the stress concentration area,and more than 68 m is the original rock stress area;when the working face advances 24 m,the distribution of in-situ stress in the stress concentration area changes,and the minimum horizontal stress is the minimum in-situ stress.(3)Based on the analysis of the basic law of the distribution of the crack zones in the stope,combined with the lithology and thickness characteristics of the various strata in the roof of the 31101 working face,the height of the collapse zone required to completely fill the goaf of the hard roof of the 31101 working face is determined and based on It is determined that the maximum hydraulic fracturing fracture height of 31101 working face is 7.5m.Combined with FLAC3 D software,the distribution rules of stope fissure zones in hard roof of working face 31101 during mining were analyzed.(4)A slotted drilling and fracturing model was established.According to the difference between the grooving direction and the minimum principal stress,three models were established.Analyze the conditions for the fracture direction change in hydraulic fracturing.(5)Based on the analysis of the stress field and fissure field of the hard roof of the 31101 working face,combined with the technical characteristics of hydraulic fracturing,a hydraulic fracturing scheme for the hard roof of the 31101 working face was proposed,and perfect safety technical measures were formulated.Effectively promote the timely collapse of the hard roof and shorten the hard roof pressing step,effectively avoid the large area of the working roof roof pressing,which is more conducive to safe production.The paper has 81 figures,19 tables and 91 references.. |
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