Experimental Investigation Into Stress-Acoustic-Deformation Evolution Of Fault Activation Process Under Coal Mining-induced Stress Paths

The fault discontinuity structure controls the deformation,failure and mechanical properties of coal and rock.The interaction between the structure and coal mining activity is crucial to affect fault activation.Aiming at the monitoring and early warning challenges of fault-induced rockburst under coal mining activities,the experimental design of mining-induced stress paths and the resultant reproduction of fault activation process were considered as the research feature.Firstly,based on the three key factors of mining-induced fault activation process,"fault,mining-induced stress and seismic-based dynamic stress",two main kinds of conceptual models for the mining-induced fault activation were abstracted and summarized: mining-induced quasi-static stress dominated fault activation and seismic-based dynamic stress dominated fault activation.Secondly,taking the field investigations and theoretical analyses as guidance,and the physical experiment as the main method,the fault activation process under coal mining-induced stress paths was systematically investigated.There are three key technologies developed: true-triaxial load-unload and dynamic-static experimental testing,passive acoustic CT detecting within AE,and contactless digital photogrammetry within high-speed camera.There are four main research contents included for the systematical investigation of fault activation process: experimental design and analytical modelling,biaxial loading and unloading experiments,true-triaxial instantaneous unloading experiments,and biaxial dynamic and static loading experiments.The purpose of this thesis is attempting to illuminate the stress-acoustic-deformation evolution of fault activation process under coal mining-induced stress paths.The results of biaxial loading and unloading experiments show that in the initial stage of loading and unloading,the rise of vertical stress triggers the sliding of cross-section,and in the later stage,the sliding is accompanied by the damage and failure of the sample,resulting in the equivalent splitting failure which is nearly perpendicular to the fault plane until it enters the stage of stick slip instability and continues to the end of the experiment.Before the overall sliding instability of fault sample,the AE ringing count rises sharply,which can be used as a precursor of fault activation.The results show that part of AE events appear in perpendicular to the fault plane,and which has a good aggrement with the high wave velocity area.A shear zone was formed during the period of fault slip,and the strain value inside presents in a non-uniform distribution,where the strain concentration area corresponds to the initial position of the equivalent splitting failure.The results of biaxial dynamic and static loading experiments show that under the action of dynamic load,the fault slip occurs at an instant,the degree of which is positively related to the strength of dynamic load,and the friction trace on the fault plane is obvious,but the analogous hanging wall and footwall of the fault sample remain intact.The scale of stress drop caused by fault activation is limited,which is closely related to whether the fault reaches the critical stress state of static load.The AE ring count mainly occurs in the early stage of loading and the later stage of stress maintaining.The ring count reaches the maximum at the dynamic loading moment,and the magnitude of value is closely related to the dynamic loading intensity.AE events mainly concentrated on the fault plane and its vicinity.The main reason is that the dynamic loading triggers fault slip and then causes the shear failure of the locking unit pre-existed in the fault contact surface.AE events mainly distribued in the high wave,and a good corresponding relationship was found between the velocity distribution and AE events.A shear zone is also formed during the fault slip period.The results of true-triaxial instantaneous unloading experiments show that under the action of instantaneous unloading,the instantaneous fault slip occurs,accompanied by one or more stress drops,which could be impeded by the horizontal stress on the other side.The AE ring count mainly occurs in the early loading stage and the later unloading stage in the stress maintaining process.The ring count reaches the maximum after the instantaneous unloading,and the magnitude of value is closely related to the horizontal stress from another side.AE events mainly concentrated in the fault plane and its vicinity.The main reason is that the instantaneous unloading triggers the fault slip and causes the shear failure of the pre-existing locking unit in the fault surface,and a good corresponding relationship was observed between AE events and high wave velocity.There are 80 figures,14 tables and 89 references in this paper.