| Based on the complex conditions in thick coal seams of No.2612 working face with large mining height at Dongpang coal mine,the mine pressure behavior,the stability of hydraulic supports and the surrounding rock control were analysed,through on-site survey,theoretical analysis,numerical simulation,physical similar simulation and in-situ measurement.The results were as shown as follows.(1)Based on the background of thesis research,the three dimensional model of No.2612 working face with large mining height was built.The mining condition of No.2612 working face was deeply researched through analyzing the burial characters,geologic feature,and other mining elements of No.2 coal seam.Stability criterion of Marshalling Beam structure in updip working face with great mining height was obtained through mechanical analysis.There is a syncline structure inside the No.2612 working face,which results in the downward mining and upward mining in wide angles.The biggest angle near the open-off cut is 27 degree,which makes the mining harder.The immediate roof of No.2612 working face is fractured siltstone strata,which thickness is more than 3 meters,and is hard to support.The Marshalling Beam structure of roof is hard to form,which caused shock load to working face and influenced the mining safety.In view of the influence from Ordovician water-bearing stratum in Dongpang coal mine,detection is very necessary during the mining.The finding of collapse column and water diversion tunnels can prevent the water disaster.At the same time,No 2612 working face belongs to abnormal area of gas emission,and the management of gas and ventilation need improve.(2)The ZY10800/30/65 D hydraulic supports are selected by No.2612 working face,and the working resistance can meet the requirement in theory.The sliding of hydraulic support with large mining height is influenced by coal seam angle,the real-time working resistance of hydraulic support,and the friction coefficient between pedestal and bottom strata.There is a non-linear relationship between limited sliding angle and real-time working resistance of hydraulic support.The thesis explains the necessary and sufficient conditions of hydraulic support sliding in working face with large mining height.The gravity positon of hydraulic supports was confilmed by field surveying,and the gravity positons in different conditions were calculated out.Through the numerical simulation,the relationship between hydraulic support and surrounding rock is analysed.The methods on keeping the stability of hydraulic support during the mining includes connecting the immediate roof,small range of droping supports and keeping the mining height of working face.(3)Based on the problems during the No 2612 working face passing the syncline structure,the stress condition of hydraulic support and the surrounding rock controlling were analysed in deep.The results showed that,in the normal downward mining working face,the the hasten forward of sliding and retroflexing of hydraulic supports is bigger than No.2612 working face,due to the 27 degree coal seam angle in tendency direction besiding the 19 degree downward angle,which is equal to fake inclined mining,and improves the stability of hydraulic support.(4)During the No.2612 working face passing the syncline structure,the incompleteness of the immediate roof was controlled by slip casting in advance in service roadways.Even the working face was leaded to normal mining path from mining immediate roof,coal seam and dirt band together,which preserves the mining order of working face.Besides,the technological problems of electromechanical equipments during the working face passing syncline structure were solved one by one through equipment transformation,which shorten the break-in time between people and equipments,and protect the mining process safe of No.2612 working face.(5)Based on the special process when No.2612 working face passing the syncline structure,the mine pressure behavior of whole process was analysed through numerical simulation,physical similar simulation and field surveying.The results of numerical simulation showed that,at the beginning of mining,there is a stress concentration appeared at the 5~15 m before coal wall,even the degree of concentration,the displacement of roof and destruction line of plastic zone were increased totally.During passing the syncline structure,the vertical stress,vertical displacement and destruction line of plastic zone were changed,and the pressure behavior was violent,wall caving was big,and the immediate roof fell.When the working face began to flat,where was far from the syncline structure,the degree of concentration,the displacement of roof and destruction line of plastic zone were smaller.The results of physical similar simulation showed that,the periodic weighting distance was smaller at upward mining than that at downward mining.During the working face changed to downward from upward,the degree of roof crushing increased,same to the intensity of pressure and working resistance of hydraulic supports.(6)Based on the precess of No.2612 working face upward mining after the syncline structure,the surrounding rock controlling techniques were analysed in system through theoretical analysis,lab testing of rock mechanical and numerical simulation.The results of pressure field observation showed that,the first caving distance of immediate roof was 16.5 m,and the first caving distance of based roof was 28 m,when the periodic weighting distance was 9~10 m in 2 or 3 days.The every distances were 15 percents shorter in nearby working face than these in No 2612 working face.The physical and mechanical parameters of coal seam and rock strata were obtained through point loading test in No.2612 working face,which included of compressive strength,strength of extension and so on.Analysis by synthesis,to the No.2 coal seam,dirt band and immediate roof strata,the strength of dirt band is biggest,which near 2.7 in Pugh coefficient,then is the immediate roof strata in 1.7,and the coal seam is 0.8 as soft coal seams.Through the analysis on failure mode,influence factors and failure law of coal wall caving in working face with large mining height,some results were obtained.The results show that,major coal wall caving appears during the base roof periodic weighting period and stop mining period,and the serious coal wall caving appears in the middle part of working face.The geometrical shape of coal wall caving is complex,and the face guards of hydraulic supports need to protect call wall during the mining.Through the numerical simulation and data analysis,the relationships between coal wall caving depth and mining height,burial depth,working resistance of hydraulic supports,joint of coal wall,dirt band and other elements were obtained.The results show that,the height 4 m is a limit to coal wall caving degree,and the depth of coal wall caving will decrease with the improving of internal friction angle in coal body joint.The technical system of complex thick coal seams mining was built in this thesis through the analysis on downward mining and upward mining of No.2612 working face with 6.5 m mining height.The results enrich the surrounding rock controlling techniques,and lay a foundation to coal mining of thick coal seams with dirt band not only in No.2612 working face at Dongpang coal mine. |
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