Damage Mechanism And Control Of Fractured Rock Mass Roadway Under Cyclic Impact Disturbance

The fractured rock mass in the disturbed area of metal mine mining is not only subjected to the static load of mining engineering structure but also subjected to the disturbance impact load of mining engineering blasting operation.The surrounding rock of the roadway close to the stope,the cyclic impact disturbance load superimposed on the existing static load,easily induces the roadway’s instability and failure.The rock mass in the far area that has not been excavated temporarily is subject to frequent impact disturbance loads.The original cracks expand and extend,resulting in impact damage.After the damage,the excavation of the rock mass leads to the change of static load,which also has a significant impact on the stability of the surrounding rock.It is of great scientific significance and engineering value to reveal the damage and deterioration mechanism of fractured rock mass under cyclic impact disturbance,and to propose a control method for surrounding rock of roadway against cyclic impact disturbance.This paper conducts a detailed investigation of the failure characteristics of the fractured rock mass roadway in Baiyinhubu Mine,analyzes the structure and mechanical inducement of the failure of the surrounding rock of different types of roadways,conducts targeted indoor cyclic impact disturbance tests,studies the deterioration characteristics and damage fracture mechanism of the fractured granite with different occurrences under cyclic impact disturbance stress,and derives the constitutive damage model of the rock mass with fracture geometric characteristics,The influence of fracture occurrence on crack propagation evolution and the failure mode is analyzed,and the stability control technology of fractured rock mass roadway is proposed.The main work and research achievements are as follows:(1)The geological environment and joint fissures of the roadway in the Baiyinhubu mining area were investigated,the characteristics and causes of roadway failure were analyzed,and it was found that the roadway failure was mainly caused by the initiation,development,and coalescence of weak joint fissures under frequent mining disturbance.The engineering problem of instability of fractured rock roadway under impact disturbance is condensed into the damage deterioration problem of fractured rock specimen under the combined action of axial pressure,confining pressure load,and cyclic impact load,including cyclic impact damage failure of fractured rock under compressive load and uniaxial compression failure of fractured rock after cyclic impact damage.(2)Aiming at the impact disturbance failure problem of unidirectional compression engineering rock mass such as ore pillar,the Hopkinson compression bar(SHPB)cyclic impact test was carried out on the cracked rock specimens under uniaxial load,and the mechanical response characteristics and degradation mechanism of rock specimens with different fracture occurrences under different impact strengths were studied.The test reveals the correlation between the angle of the prefabricated crack of rock under cyclic impact and the mechanical properties and impact resistance of rock,as well as the influence of the angle of the crack on the fracture morphology of rock.(3)To solve the problem of impact disturbance damage and failure of the surrounding rock under triaxial compression in the untapped area,the cyclic impact test of the rock under triaxial compression was carried out.The test found that the pre-axial compression reduced the dynamic deformation modulus and dynamic strength of the crack specimen,and the lateral constraint provided by the preimposed confining pressure improved the compressive strength of the rock.Therefore,the engineering rock mass structure has a stronger impact resistance under higher confining pressure.Under the impact disturbance load,the confining pressure constrains the generation and development of new cracks,and the primary cracks are mainly developed and expanded,leading to the simplification and regularization of crack growth patterns during the failure;Because of the large energy accumulation in the rock with large axial pressure,the degree of breakage is relatively high when the rock is damaged,and the risk of dynamic disaster is high.(4)Given the problems of stress redistribution and local stress concentration caused by mining excavation,which lead to excavation disturbance and initial damage and failure of rock mass,uniaxial compression tests are conducted on rock specimens after cyclic impact damage to analyze the mechanical characteristics and failure mechanism of impact damaged fractured rock mass.The internal microcracks of the rock after impact damage develop.The anti-fracture strength under compression load changes in a U-shape with the increase of the crack dip angle.The compressive strength,elastic modulus,and Poisson’s ratio of the damaged rock in the environment with large pre-imposed confining pressure are positively linear with the increase of confining pressure,and inversely proportional to the impact damage degree.During rock failure,the axial compressive stress and transverse tensile stress cause the cracks to connect,and the main cracks and the secondary cracks around them continue to expand,leading to the complete failure of the specimen.(5)Based on the characteristics of damage distribution in the specimen under cyclic impact disturbance,the impact disturbance damage effects of fracture dip and penetration on the rock are analyzed,and the impact disturbance damage constitutive model of nonpenetrating fractured rock mass is established.The macroscopic damage variables in the model take into account both the geometric characteristics of the initial crack and the effects of preloading axial pressure and confining pressure.The theoretical calculation results of the damage model are consistent with the damage variable law defined by porosity in the test results,and the fitting parameters of the model can reflect the influence of fracture structure on the mechanical behavior of rock mass.(6)Based on the above experimental and theoretical analysis results,the surrounding rock support and reinforcement technology of fractured roadway under cyclic impact disturbance is explored.The 3DEC numerical simulation method establishes the tunnel model disturbed by blasting impact.By adjusting the support structure,effectively anchoring the fractured rock mass,and transferring the peak distribution of concentrated stress,the stress,displacement,and plastic zone expansion characteristics of the damaged tunnel are analyzed.It is found that a stable plastic boundary is formed in the surrounding rock after the tunnel excavation,and the impact disturbance stress promotes the stable plastic boundary to expand outward.Based on the analysis of the influence of the fracture that occurs in the rock mass on the crack propagation evolution and failure mode,the oblique bolt support scheme is proposed for the impact-damaged roadway,which effectively strengthens the impact resistance of the damaged roadway support structure.