To Consider The Effect Time Of Forces Rock Burst Simulation Test

Rock burst is a dynamic instability failure phenomeno， due to excavationunloading the rock mass of underground engineering under the condition of highstress will come into being stress concentration in the excavation process of hardbrittle rock, when the stress is more concentrated than the limit equilibrium state, theelastic strain energy stored in the rock will burst release, which has become one of theworld’s underground engineering problems. At present, the domestic and internationalresearch on rock burst is generally based on the field monitoring and laboratory test,the test has two main limitations: one is the small test sample size under evenlydistributed load, which can not simulate rock gradient stress environment; another isthat loading process is less concerned about the time influence of stress effect. Basedon the research of Wuhan University of Technology and three institute jointlydeveloped YB-A type rock burst simulation test device, summarizing the engineeringrock burst phenomenon according to the time and place, put forward a kind ofgradient loading test method which takes the time influence of stress effect intoconsideration, then do rock burst simulation test denpend on different strength gradeand different lateral pressure coefficients. Put forward a rock burst intensity judgmenton the basis of test, analyze the mechanism of rock burst and acoustic emissioncharacteristic. The main research results:(1) based on gypsum material rock burst simulation experiment, analysis therelationship between maximum principal stress (σ) and the uniaxial compressivestrength (Rc), it is concluded laboratory rock burst intensity discriminant basis whichconsidering the time influence of stress effect,as follows:σ/Rc=1.0-1.2;slight rock burst: a crisp sound, free surface peeling, launch，phenomena;σ/Rc=1.2-1.3; moderate rock burst: crisp sound, the free surface of large area ofstripping, throwing;σ/Rc≥1.3; strong rock burst: violent noise near the free face, throwing a largearea of the region(2) The tests’ result shows: rock burst need a disturbance of out load, when therock does not reach the ultimate energy state or in the ultimate energy state, which is not occurring rockburst, when reached the limit energy storage state, if there is anexternal loads continue to exert energy on the rock,then break the limit energy storagestate, the excess energy will be to destroy the release form, for the rock massstructural integrity, high strength, good brittleness may be rock burst.(3) Different strength of rock mass’ test shows, in certain conditions, the higherthe strength of rock mass, the more elastic strain energy release, the bigger rockburstintensity generate. Many times loading stress and holding stress shows, after firstrock burst, if it continues apply external load, the rock will stored elastic strain energyagain, when the energy exceeding the limit equilibrium state again, which maycontinue to generate rock burst again. Conparising the4groups of test with thesample results without considering the effect of stress time, we can know stress timeeffect are the important influence factors of rock burst failure form, the tension andcompression type failure is the main failure form if effect forces time was under fullconsideration, and this phenomenon is similar with engineering rock burst, and theshear failure is the main failure form without considering the circumstances.(4) Analysis the rock burst emission characteristic parameter, wave and formandlocation. Draw the following conclusions:AE can be used as the rockburst precursoryevent basedment, when rock burst happens, the specimen will generate a largenumber of acoustic emission events, and havehigh energy and high amplitudewaveform generation;From gypsum laboratory rock burst simulation test, before therock burst, acoustic emission frequency spectrum characteristic is high-frequency andlow-amplitude, and there are multiple frequency zone of acoustic emissioncharacteristics; during rock burst, acoustic emission frequency spectrum characteristicbecome low-frequency and high-amplitude, frequency zone become one and range20Hz to40Hz, and the zone change to narrow; after the rock burst, acousticemission frequency spectrum characteristic in low-frequency and middle-amplitude,frequency zone is wider than rock-burst’s; Comparison of multiple groups of testsfound that the strength of the different will affect the range of frequency zone sizedifferences, the lower the strength of the rock, then the more wide frequency zonewill become a little after rock burst.Through the test of the three groups of acousticemission location map,which can judge rock burst internal micro cracks developmen,extension and penetration process, is also a sample show of the evolution of internal stress. Acoustic emission location map is match with the failure diagram of laboratorytest perfect, which has a very important role in the deep study of the failuremechanism of rock burst.(5) Using the flac3dfinite difference software, make the correct parameters,select the same stress and displacement boundary conditions with indoor test, trackthe displacement feature point and monitor the whole process yield failure state,which can verify and make up the laboratory test results. The simulation results showthat the rock burst failure is due to the tensile stresses exceed the ultimate tensilecapacity, micro cracks generated a lot of tension, and then tensile failure, which agreewell with the test results.