Research On Surrounding Rock Stability Of Roof Roadway In Ascending Mining Of Thin Seam

Based on field geological and production technique conditions of working faceNo.201in Xiaohezui Mine of Dazhu Coal Electricity Group Company in SichuanProvince, this paper adopts the method of theoretical analyses combining withnumerical simulation and field observation, researches deformation destroyingcharacteristics of overlying strata in stope and roadway deformation in working facesabove. The main research results are as follows:(1) Adopting ratio judging method,“Three Zone” discriminant method andsurrounding rock balance method, this paper analyses the feasibility of ascendingmining in2016(22) working face of Xiaohezui Mine. Analysis reaches a conclusion thatthe spacing between24coal seam and22coal seam is greater than the fracture zoneheight after22coal seam has been exploited. In addition, located above the balancedrock stratum, the spacing is able to keep balanced rock structure to avoid interlayerstagger. Hence, ascending mining is allowed to carry on and the exploiting interval timeof2016(24) working face is identified as5.9months.(2) Roadway surrounding rocks of2016(24) working face in Xiaohezui Mine areidentified as type Ⅲsurrounding rock, namely moderate stability surrounding rock,after it is classified according to monothetic classification and polytheistic classification.According to roadway bolt support theory and surrounding rock classification, thispaper proposes a kind of reinforced support named “rock bolt plus cable plus metalmesh plus steel ladder” in the basis of former support of2016(24) working face air wayin Xiaohezui Mine.(3) As goaf expand, stress of24coal seam redistributes and vertical stress can bedivided into three zones: stress concentrated zone, stress relief zone and stress stabilityzone. Distribution of support pressure above goaf is asymmetric distribution. Themaximum goes to about15meters in front of working face and5meters behindopen-off cut, the maximum peak is1.5times of in-situ stress and the stressconcentration is not severe. Stress relief zone is above the goaf, the minimum stressgoes to10meters behind working face and10meters behind open-off cut, that turns toalmost zero when working face advances50meters and the maximum subsiding is0.360meters. Stress stability zone appears above the area40meters behind workingface when working face advances80meters and waste rocks are almost compacted. The vertical stress of stress stability zone nearly equals to in-situ stress.(4) Two-sided displacement significantly reduces when adopting reinforcedsupport and roadway roof displacement decreases not obviously, which indicates thatroadway roof and floor deformation is mainly floor deformation. Under the effect ofbolting with wire mesh support, vertical pressure of roadway roof is transferred to thedeep of opposite sides of roadway. That leads to the reduction of two-sided pressure andcontributes to roadway two-sided support.(5) The exploiting of2016(22) working face has a effect on the area73metersfront and back of working face, while that reduces after reinforced support. Theadvanced support pressure of working faces below has a little effect on roadways. In thearea22meters back of working face, overlying strata fracture and separate, with severedeformation of roadway and clear separation above roadway. In the area50metersbehind working face, waste rocks are gradually compacted and roadway deformationturns to be stable.(6) There is little difference among roof displacements of different supporting areaswhen adopting ascending mining, which is close to coal subsidence of simulation. Thisresult proves that roof displacement of ascending mining is able to reflect themovements of roof overlying strata. Besides, the maximum of roof horizontaldisplacement of goaf roof roadway points to open-off cut. After the stability, thedisplacement is not going to zero, but points to the center of goaf.