Mechanism Of Clamping Rockburst In Horizontal Section Mining Of Steeply Inclined,Extra-Thick Coal Seam

Rockburst is one of the characteristic coal-rock dynamic disasters.With the increase of mining depth and intensity,rockburst disasters become more and more serious.Therein,the dynamic disasters have also occured in horizontal section mining of steeply inclined,extrathick coal seam,which seriously affects the normal safety of mine production.Therefore,it is of great significance and practical value to study the mechanism and prevention of rockbursts under sublevel mining of steeply inclined coal seam.For this reason,the rockburst mechanism of horizontal sublevel mining in steeply inclined and extra-thick coal seam was studied by field investigation,theoretical analysis,physical simulation test,numerical simulation test and engineering practice.Statistical analysis was made on the rockburst characteristics in horizontal section mining of steeply inclined,extra-thick coal seam.The coal seam in sublevel mining is clamped between the roof and floor and the dynamic appearances on both sides of roof and floor are asymmetric.There are differences between stope rockburst and roadway rockburst.The frequency of stope rockburst is less than that of roadway rockburst,while the degree of damage is greater than that of the latter.Moreover,extractive activities is the main cause of roadway rockbursts.The characteristics of load-bearing for clamped coal mass and dynamic disturbances in subsection mining were analyzed and studied.The mining stress fields of clamped coal mass can be divided into four parts,including triangular plastic zone,deep plastic zone,deep elastic zone and original stress zone.The deep plastic zone and deep elastic zone both belong to deep bearing zone,and are the main bearing zone of mining-induced stresses.When the clamped coal mass is under the mining influence of current sublevel working face,the movement activities of overlying strata and the mining-induced stresses both increase.The expression of dynamic loads induced by overburden breaking was deduced by establishing the relationship among the energy released in overburden breaking,microseismic energy,peak vibration velocity of particles and dynamic disturbances.The breaking of high key strata can lead to the synchronous breaking of lower key strata in advance.Besides,the dynamic disturbance effected on coal mass is the superposition of dynamic loads induced by multi-layer overlying strata breaking when overlying strata break synergistically.The instability types of overburden articulated structures mainly contains sliding instability,rotational deformation instability and further breakage for articulated rock blocks.The sliding instability occurs at the upper arch foot of articulated structures,while the rotational instability occurs at the lower arch foot.Dynamic loads can be also induced by the instantaneous instability of articulated structures,which is estimated according to dynamic loads of type II in coal mines.The mechanism of clamping rockburst instability in horizontal section mining of steeply inclined,extra-thick coal seam was revealed.The rockburst type and discriminant criterion of clamped coal mass suitable for subsection mining were put forward and established,including the stope rockburst type and roadway rockburst type.The occurring position of stope rockburst is inside the coal mass,while its appearing position is in the sectional working face.In addition,the occurring process of stope rockburst was reproduced and verified by similar simulation test.Based on the in-situ rockburst situation,it is verified that the dynamic lifting and extrusion of supporting floor(bottom coal)is the main cause of impact damages of hydraulic supports.Moreover,quasi-static failures of roadway surrounding rocks mainly occur at the roadway roof and floor,followed by two sides.External dynamic loads can aggravate the compression-shear failures of deep roadway surrounding rocks in high-stress zones,while shallow roadway surrounding rocks in stress-relaxed zones is mainly subjected to reflection-tension failures under dynamic loads.The roadway rockburst in near vertical coal seam shows that the chief destruction is the side heave of roadway(side heave of rock side is larger than that of coal side),followed by the floor heave and roof subsidence.The strategy of rockburst control in horizontal section mining of steeply inclined,extrathick coal seam was put forward,including comprehensive index evaluation method,monitoring and early warning system and prevention methods adapted to subsection mining.The prevention measures mainly contains: selecting reasonable subsection vertical height,determining safe relative distances of excavations,selecting type and designing parameters of supports in stope and roadway for resisting rockbursts,as well as optimizing pressure-relief schemes.The research results were applied in Yaojie No.3 coalmine,and achieved remarkable control effects and good social and economic benefits.