Rib Breakage Mechanism And Reconstruction Technique In Lagging Part Of Gob-side Entry Retaining

Displacement speed mounts dramatically under the frequent disturbance ofrotation effects incurred by lateral roof in gob-side entry retaining, and prolongedrheology still exist after the movement of main roof reaches its plateau. Deformation oflagging segment behind the working face is asymmetrical and it is characterized bylarge deformation occurring in coal rib and fierce floor heave, where the deformationof coal side accounts more than80%that of ribs. The kernel to maintain stability ofentries that lagged behind working face lies in the study on the bearing capacity ofsupporting structures and surrounding rock mass.In view of theoretical analysis, lab test, numerical simulation, industrial trial, andthe like, this dissertation presents the fractured laws of coal side and supportingstructure that lagged behind the working face. Plus, this dissertation also studies bearingcapacity of grouting aggregations in original cracked coal mass, its characteristics ofdeformation and secondary damage also been fully analyzed. Grouting timing based onfissures evolution intra the rock mass and random expansion law of grout in fissureswere also optimized, it thus put forward the reconstruction technology concerning themining-induced breakage in ribs that lagging behind working face, and the technologyis successfully applied in field trial, the research achievements is detailed as below,(1) Theoretical analysis demonstrates that rock mass neighbouring the face willconstantly disturbed by strong mining-induce pressure, where a large amount of fissuresshow out intra the surrounding rock. The fissures will in turn induce interfacialdecoupling between resin and rock mass, this decoupling also bilaterally propagatesalong the sides of fissures, hence the axial strength will exponentially decreased.Theoretical analysis testify that bolting-grouting measure is an effective technology tominimize the breakage zone in coal side as much as possible on the basis of ultimateequilibrium principle and strain softening property of coal, the predominant results isthe increased width and overall increased uniaxial compression of reinforcement zone.(2) Uniaxial compression strength is greatly improved as breakage coal isreinforced by grouting, Portland cement, sulphur aluminate cement, and superfinecement are tested respectively. Consolidation coefficient and strength recoverycoefficient of these three specimens can respectively reaches to2.55,2.15,5.28and31.43%,57.11%,85.51%. The grouting measure increases the ductility of initialbreakage coal, whose deformation resisting capability and plasticity are distinctly augmented. Confining pressure and bonding strength between grout and cracking planeare key factors which concerning with the bearing ability and secondary breakagepositions of consolidated body.(3) Relationship between grouting scope and different mining-influenced stagesare analyzed by dynamic simulating measure in gob-side entry retaining. Surfacedisplacement in the roadway shows high consistent with the laws of grouting scope,which can be referred as to judge the right timing for grouting. Borehole imaging testmanifests that the expansion degree of fissures before and behind the face is increaseddramatically, possibilities for grouting measure is also feasible during this period.Timely grouting should be conducted timely to reinforce the rock mass before thecracking area surpass the anchoring scope intra the rock mass.(4) On account of the basics consisting of overall controlling, reinforcedsupporting in certain parts, dynamic reinforcement, combination of bolting andgrouting, and timely repair, here this dissertation initiates reconstruction technicalsystem concerning bearing capacity of ribs in gob-side entry retaining lagging the faceline. According to the summarized key technologies, they are a combination of integratetechnology of bolting and grouting, grouting technology, cable combined with truss inribs, and high strength active bolting repairing technology aimed for large deformationentry in gob-side entry retaining.(5) Corresponding results have been successfully prom oted and applied in face1252(1) of Panyidong Mine, face12418of Xieqiao Mine, and face1111(1) of ZhujiMine.