Deformation And Failure Mechanism Of TBM Excavated Roadway In Deep Jointed Strata Of Coal Mine And Control Countermeasures

Underground coal mining is common in China,which demands numerous hard rock roadways.In order to improve the mechanization and intelligence of construction,many coal mines have started to introduce Tunnel Boring Machine（TBM）for the excavation of hard rock roadways.However,TBM is unfavorable to advance under adverse geological conditions,such as the strata affected by joints.Moreover,if the roadway is buried in deep strata and disturbed by the process of TBM excavation,the surrounding rock is more challenging to be well controlled.This has become an important obstacle to the wide application of TBM technology in deep coal mines.In this dissertation,the mechanical properties of jointed rock mass were revealed through mechanical tests and microscopic numerical simulations.Based on this,A 3D ubiquitous-multiple-joint constitutive model for rock mass was established.The model was embedded in numerical software for the analysis of the stability of roadway surrounding rock in the jointed strata.Using the model,the deformation and damage mechanism of the surrounding rock under the influence of joints and ground stress was studied.Based on the above analysis,control countermeasures of the surrounding rock of TBM excavated roadway in deep jointed strata were proposed.The main findings and conclusions are as follows:（1）A true triaxial test of jointed rock mass considering the stress path of TBM excavation was designed.The effects of joint dip angle,direction of principal stress and magnitude of intermediate principal stress on the mechanical properties of jointed rock masses were investigated.The strength,damage and acoustic emission characteristics of single joint rock mass under different test conditions were analyzed.The results show that the stress paths of TBM excavation can be simplified into one true triaxial conventional loading stress path and two true triaxial loading and unloading stress paths.Besides,the relative positions of principal stress and joints have significant effects on the strength of rock mass with a single joint,and the strength shows obvious anisotropic characteristics.Moreover,stress paths,principal stress directions and intermediate principal stress magnitudes affect damage modes of jointed rock masses.Whenσ2 limits the joint slip,the failure mode of jointed rock mass is more complex,and the failure of the jointed rock mass is more abrupt under the loading and unloading stress path.Finally,stress paths affect the acoustic emission pattern of jointed rock mass.Specifically,acoustic events are more significant under loading and unloading stress paths than that under conventional loading stress path.（2）Particle Flow Code was used to calibrate the microscopic mechanical parameters of rock matrix and joint according to the experimental results.Based on this,the mechanical properties of rock mass with multiple joint sets under the stress path of TBM excavation were studied.The results show that the strength of rock mass with multiple joint sets is related to the joint in the most unfavorable position.Specifically,if the normal and shear stresses on this joint plane are closer to the Mohr-Coulomb strength envelope than other joints,the joint tends to break as a priority.Besides,Crack and damage evolution in rock mass with multiple joint sets affect by different stress paths.It can be found that cracks in jointed rock mass develop and expand only at moderate to high stress levels under conventional loading stress path.However,the accumulation of damage before failure is more abrupt,and the cracks rapidly develop and expand at the beginning of test under loading and unloading stress paths.（3）A 3D ubiquitous-multiple-joint constitutive model that can describe the mechanical properties of jointed rock masses was developed.The model was embedded in FLAC^3D 6.0 software using C++and validated according to laboratory and numerical experimental results.The results show that the 3D ubiquitous-multiple-joint constitutive model can reflect the mechanical characteristics of rock mass with multiple joint sets in three-dimensional space.The validations show that the strength predicted by the model is closer to the testing results,and the failure modes predicted by the model is also accurate.（4）Using the software based on finite difference method,the effects of joint orientations,number of joint sets,cohesive strength of joint and earth stress on the stability of jointed surrounding rock mass were studied.The results show that the joint is more unfavorable to the stability of the roadway when its dip angle is smaller and strike is more parallel to the roadway axis.Besides.the volume and maximum displacement of the plastic zone in the surrounding rock increase by 384.5%and244.9%,respectively,and the failure risk of surrounding rock due to TBM excavation increases dramatically when the number of joint sets increases from 1 to 3.Moreover,the improvement of cohesive strength of joint can significantly reduce the range of plastic zone,stress redistribution and displacement of surrounding rock.Finally,overburden stresses and lateral stress coefficient also have significant effects on the stability of TBM excavated roadways in jointed strata.（5）The method of grading the surrounding rock in complex jointed strata was proposed.The damage characteristics of TBM excavated roadway in deep coal mine affected by jointed rock mass were analyzed.The simulation method of pre-grouting and reinforcement of jointed rock was proposed,and the effects of grouting parameters were analyzed.The corresponding graded control technology was proposed and validated by implementing industrial tests in the field.The results show that the surrounding rock can be divided into 5 levels,among which,the rock mass of level I is more complete and harder,and the rock mass of level II～V is affected by the joints to different degrees.Besides,the failure characteristics of the surrounding rock are mainly divided into 2 categories:tension and shear damage of joint,and extrusion flexure with large deformation damage of soft rock matrix.A graded control scheme for the surrounding rock in TBM excavated roadways affected by jointed rock mass is proposed.The implementation effect is analyzed by field industrial test.The monitoring results show that the maximum displacement of roof is 157 mm;the maximum displacement of left and right sidewall is 116 mm and 138 mm,respectively,and the displacement of different monitoring points gradually converges after 40～80 days,which verifies the reliability of the graded support scheme.There are 173 figures,45 tables,and 186 references.