| The characteristics of shallow depth and hard roof of 31101 working face in Luning Coal Mine make it difficult for the roof rock mass to cave during the coal mining face propulsion process,which is easy to cause a large area of the ceiling behind the working face,thus forming a high abutment pressure.It is easy to cause disasters such as rock pressure,which is not conducive to safe and efficient production of mines.In this paper,the 31101 working face of the mine is used as the engineering background.The physical and mechanical parameters related to the roof rock mass of the working face are measured in the laboratory,and the mine pressure behavior characteristics and the hard roof hydraulic fracturing mechanism are analyzed in detail.Based on the corresponding pre-cracking scheme of the roof,the hydraulic fracturing pre-cracking hard roof was obtained through industrial tests.According to the geological conditions,the theoretical analysis of the mine pressure behavior characteristics of the overlying strata shows the height of the caving zone of the coal mining face;according to the obtained immediate roof and main roof payloads and the limit caving interval,immediate roof first caving interval,main roof first weighting interval and periodic weighting interval are calculated;based on this,it is analyzed that the main roof of the working face is a strong type of main roof with a class III mine pressure;theoretical analysis and calculation of a reasonable roof pre-cracking height.Through theoretical analysis of the effect of hydraulic fracturing on rock softening and rock mass strength reduction,hydraulic fracturing influencing factors,hydraulic fracturing crack propagation mechanism,mechanism of directional hydraulic fracturing pre-cutting and pre-cracking roof design Key parameters such as bore azimuth,dip angle,water injection pressure value,fracturing fluid selection and fracturing range were numerically simulated using UDEC discrete element software.The theoretical research and numerical simulation results show that after the hydraulic fracturing technology pre-cracks the hard roof plate,main roof first weighting interval,periodic weighting interval and immediate roof first caving interval are reduced,and the compressive strength is significantly reduced.In this paper,the Fracturing Holes and Observation Holes of A,B and CArrangement are designed,and the construction technology of directional hydraulic fracturing pre-cutting technology is established.On the basis of the development of the hard roof pre-cracking scheme on the working face,a comprehensive safety technical measure was formulated.An industrial test was conducted on the 31101 working face.The results show that the hydraulic fracturing water injection pressure and dwell time will change with the drilling depth and lithology change;main roof first weighting interval,periodic weighting interval and immediate roof first caving interval size decrease.The compressive strength is significantly reduced;the test working surface avoids the large-area pressure phenomenon of the hard top plate,ensuring safe and efficient production of the working face.This thesis has 52 figures,20 tables and 99 references. |
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