| The occurrence conditions of underground deposits are complex,and two or more kinds of rock masses are interleaved,forming the composite rock mass in contact zone.In underground mining,some roadway and stope inevitably pass through the contact zone.Due to the difference of mechanical properties of rock mass,the composite rock mass in the contact zone occurs uncoordinated deformation,and the convergence,roof fall and spalling of two kinds of rock mass occur in different degrees.In the process of roadway excavation,the rock mass experiences complex disturbance stress paths,which aggravate the damage and failure of the composite rock mass and seriously threaten the safety and stability of the roadway.It is urgent to carry out in-depth research on the deformation and failure characteristics and mechanism of the composite rock mass in the contact zone.By means of laboratory test,numerical simulation and theoretical analysis,the uncoordinated deformation of composite rock mass in contact zone and mechanical properties under disturbed comprehensive stress paths were systematically studied.Uniaxial compression,biaxial compression and shear tests have been carried out.Combined with numerical simulation and theoretical analysis,the forms and formation mechanism of uncoordinated deformation have been studied from macro-and micro-level,the influence of uncoordinated deformation,mechanical and structural characteristics and stress state on mechanical behavior of composite rock mass is analyzed.The results show that the unconforming deformation is mainly affected by the difference of the deformation characteristics of different rocks,which is shown as the constraint parallel to the interface,the extrusion perpendicular to the interface and the shear on the interface,the derived tension-compression-shear stress is easy to cause tension-shear composite fracture.Under different conditions,the main body controlling the mechanical behavior of composite rock mass is different,resulting in three failure failure control modes: weak rock control,strong rock control and interaction control.The damage evolution characteristics of the two kinds of rocks are regular and affect the change law of mechanical parameters.The influence of intermediate principal stress on the directional deformation and the uncoordinated deformation is superposed,and the increase of intermediate principal stress will aggravate the failure of uncoordinated deformation.The results reveal the uncoordinated deformation characteristics and failure mechanism of composite rock mass under complex conditions.Numerical simulation of the excavation disturbance in contact zone is carried out under the conditions of different in-situ stress environment and occurrence characteristics of contact zone,and the disturbance stress path,its formation and influence mechanism are obtained,the uncoordinated deformation mechanism of composite rock mass is explained theoretically.The ground stress state and its relationship with the spatial orientation of roadway are the main factors affecting the characteristics of the disturbance stress path,and the inclination angle of the contact interface mainly affects the disturbance degree.The disturbance stress path includes the gradual changes of the magnitude and direction of the three principal stresses.The orientation change of the disturbance stress is affected by both the excavation stress transfer and the spatial geometry effect of the palm surface,and the spatial effect will gradually disappear with the advance of the palm surface.The disturbance of the magnitude of the principal stress occurs earlier than that of the direction.The disturbance damage has a certain time effect and directionality.The disturbed uncoordinated deformation is mainly controlled by the differential convergence of the two rock masses along the radial direction of the roadway and increases with the increase of the inclination angle of the contact interface.The research results lay a foundation for studying the effect of comprehensive stress path on the mechanical behavior of composite rock mass.The spherical discrete element model is constructed,the flexible loading boundary method is innovated,and the numerical research on the comprehensive stress path loading of rock mass is carried out,the influence mechanism of comprehensive stress path factors and disturbed stress path on mechanical behavior of composite rock mass is revealed.The results show that the stress-strain trends of composite rock mass are various under the comprehensive stress path,showing certain abrupt changes and spatial directionality,and increasing the degree of deformation anisotropy in planeε1-ε3 and plane ε2-ε3.The composite rock mass mainly produces tension cracks caused by unloading,and the stress direction affects the damage only when the rock mass is in the stress state of crack initiation and propagation.The strength of composite rock mass is affected by the degree of damage and the magnitude of stress.The damage caused by the comprehensive stress path has a weak influence on the strength,but reduces the need of damage accumulation.The uncoordinated deformation of the composite rock mass changes gradually during the loading process,resulting in complex fracture characteristics such as fracture type and orientation.The research results reveal the influence mechanism of the comprehensive stress path on the mechanical behavior of composite rock mass.The study reveals the uncoordinated deformation characteristics and failure mechanism of composite rock mass in contact zone,clarifies the influencing factors and evolution characteristics of the comprehensive stress path,and reveals the damage and failure mechanism of composite rock mass under comprehensive stress path,which provides a theoretical basis for the control of the disturbance damage of the composite rock mass in the contact zone roadway. |
