Research On Unloading Mechanism And Precursory Laws Of Failure And Instability Of Coal-rock Parting Compound Structure

Rockburst is a typical coal and rock dynamic disaster,which mainly occurs in the abnormal change areas of geological structure such as fault,fold and coal seam bifurcation.The mechanism of rockburst in coal seam bifurcation area is more complex.Focusing on the subject of unloading mechanism and precursory law of failure and instability of coal-rock parting compound structure,this thesis studied the mechanism,influencing factors and precursory characteristics of slip and fracture of coal-rock parting compound structure under unloading by means of theoretical analysis,laboratory tests,numerical simulations and engineering practice,and put forward corresponding prevention and control methods.Based on the structural characteristics of coal and rock parting in bifurcation area,the "coal-rock parting-coal" ternary series structure model was established,and the mechanical criteria and trigger conditions of coal-rock parting interface slip were derived.The results show that,the instability forms of the interface include upward slipping,stable locking and downward slipping.The three instability forms are not only affected by the inclination angle and internal friction angle of the interface,but also affected by vertical and horizontal stresses.By means of triaxial loading and unloading test and discrete element numerical simulation,the slip and fracture instability characteristics of coal-rock parting compound structure under unloading were studied.The results show that,the peak instability strength and fracture damage degree of the compound model are higher under the form of fracture instability,the torsional deformation instability characteristics of the compound model are more obvious under the form of single interface slip and fracture instability,the slip instability characteristics of the compound model are more obvious under the form of double interface slip and fracture instability.The failure and instability of coal-rock parting compound structure under unloading are characterized by "low strength and high energy release" and more obvious brittleness enhancement and fragmentation phenomenon.Based on the acoustic emission(AE)monitoring data in laboratory,using FFT spectrum analysis and HHT signal processing technology,the precursor signal characteristics of coal-rock parting compound structure failure and instability under unloading were explored.The results show that,when the interface is about to slip,the maximum amplitude of AE event increases,the dominant frequency is relatively high,the duration of the maximum amplitude is short,and the energy is concentrated in the relative high frequency range of 100 ? 200 k Hz.When the compound structure is about to lose its overall stability,the maximum amplitude of AE event reaches the maximum,the dominant frequency decreases,the maximum amplitude of waveform lasts for a long time,and the energy is concentrated in the relatively low frequency range of 50 ?100 k Hz.In addition,both the slipping of the interface and the overall instability of the compound structure will be accompanied by the sharp decrease of the energy index,the sharp increase of the cumulative apparent volume and the decrease of the b value.With the help of UDEC numerical simulation technology,the evolution process of roadway failure and instability induced by unloading in coal seam with rock parting were reproduced,and the influence of geological factors and mining technology factors on the failure and instability was studied.The results show that,the deeper the mining depth is,the greater the lateral pressure coefficient is,the faster the unloading speed is,the higher the strength of the rock parting and the coal-rock parting interface is,the higher the impact risk of the roadway is.When choosing the support form of the roadway with rock parting,bolt(cable)and patching support forms should be preferred.Based on the microseismic monitoring data of 5310 working face in Zhaolou coal mine,the precursor signal characteristics of roadway slipping and fracture coupling instability in coal seam with rock parting are studied,and the accuracy of indoor experiment and numerical results is verified.At the same time,the prevention and control methods of impact disaster caused by roadway failure and instability in coal seam with rock parting,and the engineering verification in 5304 working face was carried out,and good effect of anti-impact and pressure relief was achieved.There are 157 figures,16 tables and 170 references in this dissertation.