Mechanism And Prevention Of Rockburst In Extra-Thick Coal Seams Mining

In recent years,over 80%of rockbursts in coal mines have occurred in extra-thick coal seams,which tend to be frequent and intense.This leads to a pressing need to investigate the occurrence mechanism of rockbursts in extra-thick coal seams,thus providing a theoretical basis for prevention,control and early warning of rockburst hazard in extracting extra-thick coal seams.In this paper,several severe rockburst events occurring in extra-thick coal seams in coal mines in Xinjiang and Shandong Province are presented and discussed.These rockbursts tend to occur at the working face and the gate roads simultaneously after long incubation,which is often accompnies with large deformation of the mine roadways.For such a kind of events,field monitoring,theoretical analysis,case studies,laboratory testing and numerical modelling techniques are used to investigate the occurrence mechanism of rockbursts in extra-thick coal seams and the associated prevention and control techniques.The research results are as follows:The rockbursts occurring in extra-thick coal seams can be classified into two types:unloading-type and creep-type rockbursts.A calculation method for energy release in rockbursts is presented with coal seam thickness,and a rockburst risk evaluation method is also established based on rockburst tendency,and the ratio of dynamic and static stress.The surrounding rock for creep-type rockbursts exhibits zoning characteristics and the associated equations for the zones are derived.The mechanism of overall creep instability induced rockbursts in island longwall panels are investigated.A computational model for load transfer in island longwall panel is established and then an evaluation method for the overall creep instability induced rockbursts is proposed based on the model.Large deformation of gob-side roadways in extra-thick coal seams in deep mines can be attributed to secondary main roof breakage and rotation.A calculation method for determining the parameters of rockburst prevention boreholes is given based on energy dissipation index.A "zoning-grading"rockburst prevention and control framework is put forward to achieve joint control of rockbursts and large deformation in extra-thick coal seams with the development of a new-type advance hydraulic support.Connection roadways in mining extra-thick coal seams tend to be significantly influenced by high dynamic stress,resulting in activation of nearby faults.The activation can be divided into three stages:stress redistribution,energy accumulation and structural activation.A computational model is given to estimate abutment pressure in extremely-thick alluvium mines,providing a theoretical basis for the mine design based on rockburst prevention for extra-thick coal seams.