Study Of Mechanism And Criterion Of Rockburst Of Deeply Buried Excavation Of Hard Rockmass

For buried long tunnel at a higher initial stress field environment, rockburst issues uniqueto high in-situ stress areas, the rockburst of diversion tunnel in Qirehataer power station inXinjiang Uygur Autonomous Region is studied. Gneissic granite unloading mechanicalproperties change is research and analysised systematically. Based on the complex mechanicsof unloading stress path tests, the rock unloading strength under high stress environment,deformation, cracks and damage development and failure mechanism are studied. Based ontheory analysis, using numerical simulation technology, the mechanism of rock burst ofdiversion tunnel is summarized. The criterion of rock burst and initial stress field assessmentare determined. The influencing factors of rock burst and characterize are studied and analyzedfrom many aspects. The possibility of rockburt is predicted, the method of supporting ispresented. The main research works are as following:(1) The rockburst in the diversion tunnel is mainly partial strain rockbust. The break stylesinclude spalling, plate flaking and collapsing with long time. The main features of rock burst iscrackling sound crackle and most occured in the near side of the valley. Rock burst has obviouslag which occurred in the II rockmass generally.(2) Gneissic granite is hard brittle, which in the unloading test is more obviously. The peakstrength of granite of unloading is lower often of the the triaxial conmression test. The failurecharacteristic is affecting of the unloading speed. The basic performance of the macroscopic isshear failure mode, and tension failure locally.(3) Acoustic emission is intense to the uniaxial and triaxial compression test, which showthe brittle failure of unloading is easy to reach. Combining the results of the experimentresearch, field monitoring and numerical simulation, the stress change model of surroundingrock mass is proposed. The mechanism of rockburst preparation and development are proposedfrom the mechanical point.(4) The criterion of rock burst of Code for hydropower engineering geologicalinvestigation (GB50287-2006) and Code for engineering geological investigation of waterresources and hydropower (GB50487-2008)and m-0criterion are suitable to predicte thepossibility of rockburst of diversion tunnel. Based on the criteria of rockburst, the probability ofrockburst in the residual drainage tunnel was analyzed and predicted. The results illustrateexcess section of diversion tunnel will occur I level rockburst, locally section will occur II levelrock burst and the others section will occur II level.(5) The influence on the rockburst by buried depth, side pressure coefficient, formationlithology, excavation shape has been analyzed. Based on the study conclusion mentioned above, some valuable laws are derived. Finally, the designs of supporting of rockburst section withdifferent rockburst level were presented.