Research On Strength Evolution Of Mining Rock Mass And Bolt-rock Interaction

In essence,the problem of roadway support is determined by the surrounding rock and the bolt,and the anchoring effect depends on the coupling effect between the rock and the bolt,which is closely related to the deformation and instability of the surrounding rock and the mine geological disasters.The coal safety and intelligent mining strategies of China have posed a requirement to study the fundamental physics of rock mass strength,damage characteristics,and bolt-rock interaction.A thorough understanding of the response characteristics of bolts to rock mass damage contributes to the monitoring and predicting of roadway surrounding rock hazards.In this paper,a systematic study on the strength evolution of mining rock mass and bolt-rock interaction was carried out using indoor experiments,theoretical analysis,numerical simulation,and on-site testing.The main results achieved were as following:(1)An analytical model was established to obtain the evolution of rock pseudo-shear strength parameters during the whole loading process,and the meso-mechanism of the evolution of pseudo-shear strength parameters was revealed by simulation with particle flow code PFC^2D.Based on the Mohr-Coulomb criterion,an analytical model for obtaining the evolution of rock pseudo-shear strength parameters was established,which was applied to the analysis of the whole failure process of sandstone under triaxial compression.According to the results,it was verified that this analytical model was capable of describing the force and deformation characteristics of sandstone.On this basis,the PFC^2D was used to establish a clump particle model that can reflect the inlay and meshing effect between particles,revealing the meso-mechanism of the evolution of pseudo-rock shear strength parameters.(2)A strength model for damaged rock considering the characteristics of crack distribution was established,and the influence of different crack distribution parameter changes on rock strength was compared.Based on the assumption of the power-law distribution of the crack length and the Mori-Tanaka method,a strength model for damaged rock,which is related to the number and the average half-length of the cracks was established.Meanwhile,the discrete element software was used to simulate the influence of the change of crack distribution parameters on the strength of the rock,and the reliability of this theoretical model was verified by comparing the theoretical and simulation results.On this basis,the influence of the number and the average half-length of the cracks on the rock strength was compared.(3)The mesoscopic mechanism of the bolt debonding failure under static force was revealed by using an acoustic emission positioning test and discrete element simulation.The anchoring medium and rock mass were integrated processed to produce bolt pulling specimens,and acoustic emission positioning technology was applied to the bolt pulling test.Then,considering the existence of the bolt ribs,the discrete element simulation was carried out to not only reproduce the process of bolt pulling test but also analyze the influence of the distributed cracks in the rock mass on the debonding of the bolt.By analyzing the results of acoustic emission positioning and discrete element simulation,it is determined that the dilatancy and softening effects caused by the action of the bolt ribs are the main reason for the failure of bolt debonding under the action of static force.(4)A new method of using the lateral vibration frequency of the bolt to detect the strength of the rock mass was proposed,and the feasibility of this method was verified.Through the integrated treatment of the anchoring medium and the rock mass and ignoring the influence of the axial bolt load,the lateral vibration equation of the bolt coupled with the rock mass was deduced,and the quantitative relationship between the lateral vibration frequency of the bolt and the rock mass strength was established.Moreover,the self-designed bolt frequency detection system was used to carry out indoor inspection tests to obtain the response of the vibration frequency of the bolt to the strength and internal defects of the rock mass,which verified the usage value of the proposed detection method.(5)On the basis of the above research,numerical simulation,field measurement and laboratory test were used to analyze the response law of mechanical properties of bolt to rock mass damage and mine hazard.Based on the actual engineering situation and considering the influence of the fault,a numerical model was established using the finite difference software FLAC^3D to simulate and calculate the coal seam mining process,and the corresponding relationship between bolt support characteristics and deformation and damage of rock mass was discussed.Based on the results of field observation,the response of the change of the axial bolt load to roadway surrounding rock hazards such as the collapse of roadway and main roof was analyzed.There are 115 figures,28 tables,and 261 references in this dissertation.