| Based on the engineering background of 1307 coal mining face in Zhaozhuang Coal Mine,this dissertation intended to present solutions for coal rib spalling problem in large-mining-height working face,thus grouting reinforcement trial utilizing ultralong boreholes could be conducted.Start from the spalling mechanism of large-mining-height working face,following topics were studied in this dissertation:control technology for coal rib spalling was discussed;numerical simulation analysis on ultralong borehole grouting reinforcement was conducted;long-distance-grouting mechanism was researched;long-distance-grouting material and relevant borehole-sealing material were prepared;sequential borehole shaping technology for long-distance-grouting was built;correlated apparatus utilized during grouting procedure,grouting parameters,organization and management were also investigated.Obtained results were eventually applied in 1307 coal mining face in Zhaozhuang Coal Mine,1306 coal mining face in Sihe Coal Mine,and 4312 coal mining face in Changping Coal Mine,the desired effects was acquired.The main conclusions to this dissertation were listed as below.(1)1307 coal mining face in Zhaozhuang Coal Mine belonged to a typical large-mining-height working face,occurrence of coal seam was stable whilst the structure was complex,mechanical properties of coal seam and it's neighbouring strata were relatively unstable.The spalling mechanism of coal rib in working face was probed based on pressure bar stability theory,and the influencing factors of coal rib spalling was analyzed.Grouting reinforcement technology was put forward and fundamental rationales were built,mechanical model and theoretical analysis for principle grouting rationales were conducted.(2)Numerical simulation results indicated that the drastic influencing zone of abutment pressure was 20 m in front of mining face,and a range between 30 m and 40 m in front of mining face belonged to stress slowly reducing zone,where a grouting operation was most feasible and a desired reinforcement effects could be brought about.The results also proved that fully grouting in coal seam and roof would doubled the peak stress inner coal r-ib as compared with non-grouting scheme,plus,the self-stability would also be enormously enhanced,and the horizontal displacement and horizon separation strain could be effectively restrained.Numerical results disclosed that halt production or an over slow advancing speed of mining face could directly lead to large areas of spalling of coal rib7 and this situation might keep deteriorating as time went by.On the contrary,if the speed accelerated,then the mining-induced pressure would be weakened.If the advancing speed ascended,then abutment pressure inner coal rib expressed a small-scale increment,nonetheless,it belonged to controllable range,which ensured the possibility of accelerating advancing speed of mining face.(3)Inorganic single-fluid grouting material was prepared with final raito set as:superfine 52.5 Portland cement 100%,composite retarder 2%,and composite eariy-strength admixture 2%,water-to-cement ratio 0.6:1.The liquidity was favorable in the first 30?40 min and then was disabled in the following 2?3 h,the solidification occurred appropriate 10 h later.The penetration radius could reach to 5?8 m.Compression strength 1 d later was 19 MPa,3 d later was 28 MPa,and 7 d later was 32 MPa.The long borehole sealing material was also prepared,the recommended water-to-cement ratio was 1:1,time for lost liquidity was 10?15 min,hardening time was 40?50 min.Compression strength 2 h later was 8.5 MPa,the final compression strength was 12.9 MPa,this sealing material was recommended for emergency treatment of shallow sealing between 30?40 m inner rib and grout leakage occasions.(4)The theorem of "primary focus on coal rib,considering roof stability simultaneously" was proposed.Set grouting boreholes in coal rib in front of working face,and angle of elevation was also considered,thus roof could be simultaneously reinforced as coal rib was under grouting.The depth of the two rows of boreholes respectively set in entry 13071 and entry 13072 was 115 m or so,the diameter was 75 mm.Interval between boreholes was 10 m to form a triangle pattern.Angle of elevation for lower row of boreholes and upper row of boreholes was 1° and 2°,respectively.Lower row of boreholes and upper row of boreholes in entry 13071 had a distance of 2.5 m and 5.5 m to floor,respectively;As for equivalent values in entry 13072,they were 1.0 m and 3.0 m to floor,respectively.The sequential borehole shaping scheme was raised and the borehole sealing technology was studied,the grouting pump for borehole sealing procedure was modified and then specified by simplified system and compact structure.(5)115-meter-long ultralong boreholes were completed by normal drilling rig,the"two-time holes boring and two-time grouting" methodical way was proposed.After grouting procedure,coal rib spalling distinctly decreased in entries 13071 and 13072,the compactness of roof was perferable.Compared with un-grouted areas,the roof caving rate decreased 86%,chemical grout utilized on coal face to auxiliarily stabilize the coal cutting face reduced 4318 buckets.Advancing speed of coal mining face arose from 3.1 cuts per day to 4.9 cuts per day as compared with severe caving area.Plus,borehole imaging results indicated that borehole stability could be sustained and inner wall of borehole was compact,thus the overall stability of coal was enormously improved.(6)Field industrial trial brought conspicuous economic and social benefits,cost comparison pointed out that prepared grouting material could save 351,495 US dollar as least.In addiction,the proposed material in this dissertation belong to environmentally inorganic material specified by non-toxice non-corrosive properties,and without safety concerns.Technological system of ultralong boreholes in large-mining-height fully mechanized coal mining face was successively applied in 1307 working face of Zhaozhuang Coal Mine.Subsequent trials in 5311 working face of the same coal mine,1306 large-mining-height working face of Sihe Coal Ming,hidden geological structure detection in 4312 working face of Changping Coal Mine were also proved as big successes,paramount engineering application effects was achieved. |
PDF Full Text Request