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

The occurrence of rock parting exacerbated the complexity of the coal seam,and changed the physical and mechanical parameters of the coal-rock structure,which lead to the abnormality of strata behavior in mine stope.Based on the “coal-rock partingcoal” compound structure,this dissertation investigated the failure and instability mechanism,the evolution law of macro-and meso-parameter and characteristic of the precursor signals,and the multi-factors influencing mechanism of the coal-rock parting compound structure systemically,by means of theoretical analysis,laboratory test,numerical simulation and engineering practice.Failure and Instability mechanical model of the coal-rock parting compound structure based on Mohr-Coulomb criterion and complex mechanical conditions nearby free space was established,and the instability mechanical criterion of the compound structure was also presented.The results show that,the fracture and instability of the compound structure is related to both the discontinuities condition and the mechanical environment.When the discontinuities condition and the mechanical environment can not meet the criterion of slip,the instability of the structural is characterized by fracture of coal and rock;when only one discontinuity meets the criterion of slip,the instability of the structural is characterized by single discontinuity slip and fracture of coal and rock;when both discontinuities meet the criterion of slip,the instability of the structural is characterized by double discontinuities slip and fracture of coal and rock.In addition,the dynamic loading disturbance can promote the instability of the structure by changing the magnitude and direction of the principal stress,as well as the friction properties of the discontinuities,and at the same time,it can change the instability form of the structure.The failure and instability mechanism of the coal-rock parting compound structure was studied by means of uniaxial compression test and numerical simulation with Particle Flow Code,and the main instability forms of the compound structure were put forward.The results show that,instability with fracture of coal and rock is mainly caused by the shear of the discontinuities and the stress concentration resulted from the height ratio difference of coal to rock;instability with single discontinuity slip and fracture of coal and rock is mainly caused by slip and shear of the discontinuity and the stress concentration resulted from the height ratio difference of coal to rock,as well as the slip torsion;instability with double discontinuities slip and fracture of coal and rock is mainly caused by slip and shear of the discontinuities.In addition,dynamic loading disturbance promotes the deformation and fracture of the compound structure,as well as the slip of the discontinuities,and it also accelerates the instability of the structure.The evolution law of deformation,cracks development and stress distribution during instability of the coal-rock parting compound structure,as well as the dynamic instability characteristics of the compound structure were revealed based on acoustic emission(AE)data monitoring and parameters tracking during numerical simulation,and the characteristic of “high energy release under low stress” during single discontinuity slip(stick-slip)accompanied with fracture of coal and rock was also pointed out.According to the evolution law of the parameters,it was proposed that,the stress response,cracks development and energy release during instability of the compound structure mainly undergo four stages: stability-instability begins to occurtransient stability-instability.At the same time,based on the energy storage process before instability,the instability precursors characteristic of the compound structure are proposed: 1)slowed down of stress fluctuation,cracks development and energy release;2)the b value of AE events decreases rapidly from high value;and 3)relatively lower value of the faults total area appears.The multi-factors influencing mechanism on instability strength of the coal-rock parting compound structure was put forward,and it pointed out that,the instability strength of the compound structure is mainly affected by the discontinuities dip angle,discontinuities roughness,stress loading speed,strength of coal and rock,as well as the initial static stress level before dynamic loading,frequency and amplitude of dynamic loading.Among them,the influence of discontinuities dip angle,stress loading speed and dynamic loading disturbance is greater on the instability strength of the structure.Based on a strong tremor in the 1307 working face of Zhaolou coal mine with a probability of rockburst and the characteristic of AE parameters during mining process of rock parting inclusion area in the 7301 working face with a strong probability of rockburst,the disaster-causing mechanism and precursors characteristic of coal-rock discontinuities fracture and slip were verified,and the rockburst hazard control methods for rock parting inclusion area in the working face with a probability of rockburst was also put forward.There are 149 figures,17 tables,and 208 references in this dissertation.