| China is rich in coal resources with a buried depth of more than 1000 m,which are mainly located in the central and eastern regions.Compared with the shallow coal mines,the biggest characteristics of the coal mines with 1000 m deep are high in-situ stress and strong influence of mining.After the excavation of the roadway,it is characterized by large deformation,long duration and poor stability.Due to the influence of mining at the working face,the deformation and damage of the surrounding rock are further intensified,and even disasters such as roof fall and rock burst occur.The surrounding rock control methods and technology suitable for medium deep and shallow coal mines cannot solve the difficult problems at 1000 m deep coal mines.Therefore,the rock large deformation mechanism and the synergy strata control idea and technology with bolting-modification-destressing for 1000 m deep coal mines were studied by means of theoretical analysis,laboratory tests,similar material model tests,numerical simulation and underground field experiments on the basis of the haulage entry at the 1000 m deep working face No.121302 located in the Kouzidong coal mine,Xinji Energy Co.,Ltd,China National Coal Group,which provided fundation for the surrounding rock control in synergy around the roadways at the 1000 m deep coal mines.The research contents includes the following five aspects:(1)Research on the rock large deformation mechanism around roadways at the 1000 m deep coal mines from multiple perspectives such as in-situ stress,surrounding rock cracking,extra-long mining induced affect,rock dilatancy caused by deviatoric stresses and so on.(2)Similar material model tests were carried out to comparatively study the stress,fracture distribution and deformation of surrounding rock and support body around roadways with single bolt and cable support and those with synergy strata control with boltingmodification-destressing.(3)The rock deformation and failure mechanism around roadways with single bolt and cable support and those with synergy strata control with bolting-modification-destressing and other measures was studies through numerical simulation and the synergy strata control idea with bolting-modification-destressing was put forward for the roadways at the 1000 m deep coal mines.(4)Research and development the roadway synergy control technology with bolting-modificationdestressing for the roadways at the 1000 m deep coal mines.(5)The rock control pattern and parameters were put forward with bolting-modification-destressing for the experimental entry in the Kouzidong coal mine,and the field experiment and monitoring were conducted to verify the research outcomes.Through research by the thesis,the following conclusions were obtained:(1)The in-situ stress was measured in test roadway of the Kouzidong coal mine,The data point out that: the maximum horizontal principal stress was 21.84 MPa,and the vertical stress was 25.12 MPa,the in-situ stress field was dominated by vertical stress.Laboratory tests show that the roof and floor of the 13-1 coal seam were dominated by mudstone,which has low strength and poor cementability.The clay mineral content in the coal and rock accounts for 60% of the total mineral content except coal quality,which was very easy to weather and soften with water.The in-situ measurements indicated that: the main deformation of roadway were large deformation and strong floor heave,a large number bolts and cables were broken,which at the corner between roof and side wall,the plates were turned over,and the steel belts were torn,resulting in damage and failure of the support.(2)The influence mechanism of geomechanics and production conditions on the rock large deformation around roadways at the 1000 m deep coal mines with different in-situ stress,mining face length and deviating stress was studied by numerical simulation,and the rock large deformation mechanism around roadways at the 1000 m deep coal mines and its three main influencing factors which were high in-situ stress,softrock and rheology and strong mining indused of the ultra-long mining face were revealed.Based on this,the synergy strata control with bolting(bolts and cables)-modification-(grouting)-destressing(hydraulic fracture)and the “three actives” principle for the soft rock roadway in 1000 m deep coal mines are proposed.Highprestressed rock bolt and anchor were used to achieve active support,high-pressure split grouting was implemented to actively modify the weak broken coal seam,abutment stress relief was realized based on advanced hydraulic fracturing.(3)Similar material model test results showed that: the first caving interval of the immediate roof was 30 m,the first weighting interval of the main roof was 55 m,and the periodic weighting laged behind the working face by 5m.Under the influence of high stress and the mudstone roof,the roof falled along with the working face mining.The collapse and fracture morphology of overlying strata were compared and analyzed in the case of non-fracturing and fracturing.When hydraulic fracturing was not used to destress,a fracture line was generated on the roof above the coal pillar due to the influence of working face mining.After hydraulic fracturing was adopted to destress,two fracture lines wer generated on the roof above the coal pillar,and an obvious fracture and several small fractures were generated in the fracturing range,which reduces the hanging range of the overlying hard rock,the pre-existing fractures were activated,the mining stress of the coal pillar was reduced,and thus the influence of strong mining was weakened.(4)Similar material model tests obtained the stress,roadway deformation and failure characteristics of surrounding rock and support body under two schemes of bolt and cable support and synergy strata control with bolting-modification-destressing.Compared with bolt and cable support,with the synergy strata control with boltingmodification-destressing,the roadway surrounding rock bearing capacity was strengthened,bolt and cable force was increased,roadway surrounding rock integrity,strength,and the anchoring force were improved,mine-induced stress was reduced,surrounding rock fracture distribution,length,width were decreased,and there was a synergistic and complementary relationship between support,modification and destressing.The roadway section shrinkage rate was 30.8% after adopting synergy strata control with bolting-modification-destressing.The reduction rate of cross-section was 61.5% lower than that of bolt and cable support alone.(5)The stress,deformation and fractures characteristics of roadway surrounding rock under bolting-grouting-destressing cooperative control are studied by numerica simulation,and compared with the no support and rock bolt & anchor support model.Synergy strata control with bolting-modification-destressing could significantly increase the vertical stress of rock mass around the roadway,while the vertical stress in the area from the middle of the coal pillar to the gob area and the deep area of the solid coal was lower than that of no support and rock bolt & anchor support model,roadway surrounding rock deformation and cracks number were significantly decreased.(6)The synergy strata control idea with bolting-modification-destressing was proposed.Timely and actively of high-prestressed rock bolt and anchor support could effectively reduce the partial stress and stress gradient in the shallow part of roadway surrounding rock,suppression of discontinuous and uncoordinated expansion deformation of surrounding rock in anchoring area.High-pressure splitting grouting could improve the strength,integrity and anchor ability of coal.Before coal mining,selected a reasonable location for hydraulic fracturing to form hydraulic fractures,activate primary fractures,reduce the lateral side and gob overhang of the upper stratum,which could significantly reduce the mining stress value and its distribution.The combined effect of the three factors could significantly control the large deformation of the surrounding rock around roadways at the 1000 m deep coal mines.(7)The synergy strata control with bolting-modification-destressing was developed: The CRMG700 rock bolt rebar with extra-high strength and high impact toughness was developed,and the creep characteristics,mechanical response features of the bolt under tension,shear,torsion,bending,impact load and various combination were revealed.The properties of micro-nano inorganic and organic grouting composite materials were studied,the shear strength of the material modified by grouting was improved by 81.5% compared with that of ungrouting fractured raw coal,which could improve the strength,integrity of the coal structure plane and the anchoring performance of bolt and cable.The high pressure split grouting field experiment was conducted.The segmentation fracturing technology and effect evaluation method for hydraulic fracturing were put forward.(8)The rock control pattern and parameters were put forward with boltingmodification-destressing for the experimental entry,and the field experiment and ground pressure monitoring were conducted.The results showed that compared with the original support,after the application of the rock control pattern with boltingmodification-destressing,the active supporting function of bolts and cables was fully exerted,and the broken percentage of bolts and cables was reduced by 90%;the strength and integrity of the rib coal body were improved by the high pressure split grouting;the value and change of the working face's advanced mining-induced stress were reduced and the working resistance of the hydraulic support were decreased by the hydraulic fracture in the hard rock strata on the roof;the entry deformation was decreased by more than 50%. |
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