Study On The Process Of Remotely Triggered Rockbursts Induced By Dynamic Disturbances With Low Strain Rates

During the construction of deep underground projects,the excavation induced highly stressed surrounding rock frequently subjects to dynamic disturbances with low strain rates deriving from blasting(after attenution of stress wave),vehicle vibration,and seismic events,thus to induce the remotely triggered rockburst hazards,which are charactered by violent fragments ejection.The remotely triggered rockbursts with their high temporal and spatial randomness and servere destructiveness,have seriously threatened the safety of deep underground construction and they have become problems in urgent need to be solved during deep underground construction.Therefore,this paper is devoted to conduct study on the process of the remotely triggered rockbursts by indoor true triaxial tests,theoretical analysis and 3D discrete element numerical simulation.The main research contents are as follows:(1)A true triaxial test method of rockbursts triggered by dynamic disturbances with low strain rates was proposed:based on the concept of the representative rock elements(RREs),granite samples with large thickness were used to simulate the large volume rock mass in a certain area near the excavation boundary to resolve the key issue of research object selection of remotely triggered rockbursts;a loading path of "one face free-five five faces static loaded-tangential(z direction)dynamically disturbed" was used to solve the key issues of stress path and boundary conditions and coupled dynamic and static loading of remotely triggered rockbursts.Then a new high pressure servo dynamic true triaxial rockburst testing machine was used to conduct experimental study of the remotely triggered rockbursts.(2)Based on experimental study of rockbursts triggered by three types of low strain rate dynamic disturbances,i.e.,the ramp,small amplitude cyclic and the tiny amplitude cyclic dynamic disturbances,the effects of static tangential,axial and radial stresses,the dynamic disturbance amplitude and frequency on rockburst were quantitatively studied.According to the test results,we discovered the deformation condition of the occurrence of the small amplitude cyclic dynamically-triggered rockbursts,established the relationship between the stable failure and rockburst of rock in critical stress state disturbed by tiny amplitude cyclic dynamic disturbance,revealed the evolution law of rock damage and the energy mechanisms during the process of rockbursts triggered by different types of dynamic disturbances,explained the differences of the fracture characteristics of the fragments between rockbursts triggered by different types of dynamic disturbances.(3)A 3D Three-Stages-Model(TSM)of discrete element method for simulation of remotely triggered rockbursts was proposed,and it can overcome the defects of the difficulty in simulating the cracking and failure process of remotely triggered rockbursts and that in calculating the kinetic energy in traditional rockburst simulation methods.Therefore,quantitative simulation of the process of rockbursts triggered by different types of dynamic disturbances was realized.Then TSM was adopted to quantitatively analyze the evolution law of rock damage,energy,the increase of tensile and shear cracks,and the spatial distribution of tensile and shear cracks during the process of remotely triggered rockbursts,and the failure modes and the main fracture mechanisms of rockbursts triggered by different types of dynamic disturbances were revealed.(4)Based on detailed comparative analysis of the remotely triggered rockbursts and the failure of rock under coupled static and high strain rate impact loading,it was found out that,there are many significant differences in perspective of stress-strain responses,failure forms of the samples and the energy absorption and release characteristics of the samples in the post-peak stage between the failures of rock under those two coupled static and dynamic loading conditions.Therefore,most of the research results of current study of rock failure under coupled static and dynamic loading are not fully applicable to the study of remotely triggered rockbursts.(5)By summarizing of the research results,the evolution laws of rock damage and energy,the characteristics of the cracking and failure process,the failure modes and the main fracture mechanisms during the process of rockbursts triggered by three types of dynamic disturbances were revealed,and then we put forward the timely support,life cycle support and enhancing the tensile strength of the surrounding rock support principles for support design of the remotely triggered rockbursts.