Research On Failure Characteristics And Control Ways Of Roadways Extremely Close Distance Coal

In the mining of coal resources,coal enterprises will give priority to the more accessible coal seams,according to limitations such as geological conditions of mine shaft,mining technologies and difficulties.The increasing demand of coal resources makes the more accessible coal seams dried up gradually,so that some coal seams which are difficult to be exploited are coming back into people's view.The advancement of mining theories and supporting technologies enable people to mine the extremely contiguous seams in relative safety,which can avoid wasting coal resources and promote the mine service-life.The extremely contiguous seams in China are widely distributed,most of which are descending mining.In the method,the floor of upper coal seam is generally taken as the roof of lower one.When mining the lower coal seam is easily affected by superimposed mining-induced stress.The effect will be more obvious especially in the extremely contiguous seams where the spacing is smaller.In addition,the overlying coal pillars will focus their stresses on the lower coal seam through the floor of the upper ones,and form a stress-concentrated area in local positions of lower ones.There are more complex stresses on the lower coal seam so that causing difficulties to the support of head entry of lower coal seams.Taking the Xinwang Coal Mine of Shanxi as the background,the characteristics and mechanism of destroy and technologies of surrounding rock control in mining roadway in 3101 head entry under extremely contiguous seams are studied,with an integration of laboratory experiments,theory analysis,numerical simulation and industrial application.Followings are the main achievements:(1)According to peeping experiment of coal seam roof drilling,the roof of No.3 coal seam,which is under the remaining pillars of overlying coal,is loose and broken.A large number of cracks appear locally and the overall strength of the roof is relatively low with the weak bearing capacity.The roof of No.3 coal seam under the goaf has relatively complete hole walls with only a few cracks.The integrity of the roof is also well.(2)According to the Elastoplastic Theory and Slip Line Field Theory,it is concluded that the breakage depth of the coal floor,after the mining of upper No.2 coal seam,has seriously influenced the stability of the surrounding rock of the roof in No.3 coal roadway.The damage depth of No.2 coal seam to the floor is 8.14 m,which is more than the maximum spacing between two coal seams of 5.8m,showing that the mining of the upper coal seam has caused damage to the roof of the lower ones.(3)Due to the stress concentration on the coal pillars,the stresses on the roof and two sides of the haulage way are significantly increased.There are a large amount of shear failure and a certain tensile failure.The roof sinks significantly,and the two sides are severely damaged.The influence of the position of the coal pillars above the roadway roof on the range of the roadway plastic zone are discussed.The closer to the center of the coal pillar,the more obvious the range of the plastic zone.(4)Combined bolting and grouting supporting is adopted for the destruction characteristics of haulage way,and the support parameters are optimized through numerical simulation.When the row spacing between grouting anchors is set at 2000 mm × 2000 mm and the anchor depth is 4.0 m,the support effect is the best.(5)Under the focused stress of coal pillars,the haulage way is significantly damaged on the sides,point angle and roof near the coal pillar,which is called “reinforced support”.As the original support scheme cannot meet the requirements in this particular case,three kinds of support schemes to deal with different coal pillar positions above the roof of roadway are proposed,and anchor support is carried out on the “reinforced support” of the surrounding rock.(6)The maximum deformation of every key part of roadway in the three support schemes are studied and compared through numerical simulation.It is concluded that when the haulage way is directly under the coal pillar,the control validation of the surrounding rock deformation is the best.And the supporting scheme under this position is numerically simulated that the effect meets the demands of engineering application.(7)The roadway is arranged directly under the remaining coal pillars and is under the mineral pressure observation.The results show the stress of roadway bolts under the coal pillars,the deformation of the surrounding rock and the amount of roof separation.The comparison between the old and new support schemes has further verified the reliability of the bolt-grouting combined support scheme,and effectively controlled the stability of surrounding rock in haulage way in the 3101 working face.