Research On Roof Striped Weakening Method For Rockburst Prevention In Roadway

Rock burst disaster occurred in the roadways is seen as one of the major challenges in our country.Previous studies have shown that the bursting liability(internal cause)and stress(external cause)of coal-rock mass are the fundamental disaster factors that lead to roadway rockburst.Therefore,stress controlling and coal-rock masses modification have become the most direct means to deal with roadway rockburst.Roof Striped Weakening Method(RSWM)has been proposed to cope with the roadway rockburst,which also has been researched systematicly.This research developed the mechanical model under the three-directional stress considering the sectional damage pattern of the roadway,derived the stress and energy criteria for rockburst disaster.The energy storage and energy consumption characteristics of coal-rockmasses,occurred in of roof striped weakening range,are compared and analyzed with elastic mechanics,which revealed the anti-bursting mechanism of the RSWM theoretically.The rockburst preventing mechanism was verified by mechanical experiment and numerical simulation,and the influence mechanism of different parameters on anti-bursting effect is obtained.The obtained results are as follows:(1)The differential response characteristics of roadway surrounding rockmass are analyzed,and the stress and energy criteria for rock burst disaster were derived.Sudden failures can take place when the load exceeds the limit of the main load-bearing rock plate,resulting in an outward force greater than the resistance from the broken zone and a part of the plastic zone to trigger rock burst disasters;rock burst can occur when the released energy from the failure of the main load-bearing rock plate is larger than the work done by resistance.(2)The application condition and realization path of RSWM were clarified.RSWM,aiming to cope with the occurrence condition of hard roofs,means that a stripe weakening range parallel to the axial direction of the roadway is artificially created in the hard roof directly above the roadway within a certain range.The RSWM can been acheieved according to ultra-long borehole hydro-fracking method.(3)The anti-bursting mechanism of the roof strip weakening method is discussed.The roof striped weakening method can form striped weakening sections parallel to the roadway axial direction in a certain part of the hard roof;the method can reduce the elastic module of the hard roof to store less energy;the fractures in the striped weakening section may further develop under the combined impact of static and dynamic loading,and the movement between the fractured cubes can contribute to energy dissipation;the striped weakening approach can decrease the elastic module and the sub-layer thickness,which alters the upper spatial structure of the goaf roof at the ends of the roadways and achieves local structural adjustment.(4)Striped weakening zone has been simplified as bedding interfaces in coal-rock combination,then analyzing the influence characteristics of bedding interface on the mechanical behavior of coal and rock mass.Under the uniaxial compression condition,the interfaces of the coal-rockpresents a certain energy dissipation.The overall strength of the coal-rock assembly is further reduced with a greater number of interfaces;With the triaxial compression condition,the coal-rock assembly demonstrates a damage trend from brittle to ductile and then to brittle failures;With the increase of the interfaces,the triaxial strength of the coal-rock assembly decreases.when the number of the layer interfaces is constant,the reflected energy decreases and more energy is absorbed as the layer interface moves from the top to bottom.(5)The influence of roof striped weakening zone on stress wave propagation is analyzed by means of numerical simulation.The presence of the striped weakening section can lead to a high reflection of stress wave from the outside,causing obvious damages in the upper strata;the stress wave is greatly dissipated in the striped weakening section,and the stress wave decay increases with the increase of the striped height and weakening effect in a certain range;the stress degree,bolt stress,and the damage range are clearly reduced when the stress wave travels through the striped weakening section.(6)Based on the combined structural section of the central main roadway of the Mengcun coal mine,the striped weakening section can be formed by adopting the backward hydraulic fracturing using ultra-long boreholes,and an obvious increase of the AE energy can be observed during the fracturing.However,the micro-seismic energy and AE are found to reduce significantly when the proposed measure is applied,with no E>10~4J micro-seismic events observed,demonstrating that the proposed roof striped weakening approach can effectively prevent rock burst disasters in the combined structural section of the central main roadway of the Mengcun coal mine.