Abstract
Stability of the retained goaf-side gateroad (RGSG) is influenced mainly by the movements of the roof strata near coal seam after coalface passes by. To make effective controlling technology for the stability of the RGSG, we analyze the roof structure over the RGSG to illustrate the mechanism causing the RGSG instability under different roof conditions. We then examine the dynamic evolution of the deformation and abutment stress in the rock surrounding the RGSG during coal seam mining, using the FLAC3D numerical software to reveal the instability characteristics of the RGSG under different roof conditions. Next, corresponding stability controlling technologies for the RGSGs are proposed and tested in three typical deep underground coalmines. Results show that: sink and rotation of the roof cantilever over the RGSG impose severer influence on the stability of the RGSG. The RGSG suffers disturbances three times during the coal-seam mining, and the deformation and abutment stress in the rock surrounding the RGSG increase significantly when the main roof becomes thicker and the immediate roof becomes thinner. Staged support technology involving grout cable bolts has better controlling results of the RGSG stability than that composed of conventional rock bolts, when the RGSG is beneath weak immediate roof with large thickness. Roof structure optimizing technology involving pre-split technology can improve the stability of the RGSG effectively when the RGSG is covered by hard main roof with large thickness directly.
Highlights
The high stress in the deep environment requires larger gateroad protection coal pillars between two adjacent longwall panels to bear the heavy weight of the overlying strata
GSG defoBramseedd,obnrtohkise,nthaenedvoshluotwionedofptlhaestaibcubtemheanvtiostrreusnsd1e0rmthinesiindfleutheencReGoSfGthriegchot asild-seewamall mwainsisnegle.cTtehde rock locaatsedthfearreferoremnctehiendsiucarrtoorutnodidinegntrifoyctkhesuinrflauceencweaosf sdtiiflflersetanbt rleooafncdonadbilteiotnos boneatrhelaarbguetmsternetssetrse.ssBased on tdhiisstr, ibthuetioenv.olution of the abutment stress 10 m inside the retained goaf-side gateroad (RGSG) right sidewall was selected as the reAfsersehnocweniinndFiicgautroer1t0o, thideepnotsiiftyionthwehienrfle utheenacbeuotmf ednitffsetrreesnststraorotefdctoonindcitrieoansesmoonveths efuartbhuertment stresfrsodmistthreibcuoatilofanc.e as the thickness of the main roof increased and that of the immediate roof decreased
When the roof condition changed from I to VII, the abutment stress increased from 25.7 MPa to 30.4 MPa 20 m before the coalface, from 28.2 MPa to 37.6 MPa when the coalface pSausstsaeindabbilyit,yfr2o01m7, 93,91.6471MPa to 43.5 MPa 60 m behind the coalface, and from 41.0 MPa to 44.812MoPf 1a9 120 m behind the coalface
Summary
For sustainable utilization of limited coal resources, it is important to increase the coal recovery rate and reduce gas emission from the underground mining area [1]. U type longwall mining (Figure 1a) has been widely used in underground coalmines for its high productivity and recovery rate. The high stress in the deep environment requires larger gateroad protection coal pillars between two adjacent longwall panels to bear the heavy weight of the overlying strata. The movement of the strata overlying the longwall goaf forms a roof cantilever along the goaf sideT, uhnedmerovwehmicehntthoef tRhGe SsGtraitsaloovcaetrelydi.nBgetchaeusloentghwe awlleiggohatfofof rtmhescaarnotoilfevcaenr tailnedveorvaelrolynigntghsetrgaotaafisside, utnodoelrarwgehifcohr tthhee eRxGisStiGngisrlooacdastiedde. Sustainability 2017, 9, 1671 geological conditions of an underground coalmine with depth of 1000 m in eastern China, using FLAC3D software [17], and several considerations involved in this simulation are listed as follows.
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