| Wth the development of our social economy, people’s demand for resources andliving space become higher and higher, the large-scale deep mining of mineralresources, deep tunnel excavation, and defense protection engineering of deepunderground engineering, must be further deep. However, the deep undergroundengineering is accompanied by rock burst, which is a common disaster, increased withthe increase of buried depth or stress level. The frequent occurrence of rock burst istrend of deep underground engineering in our country.Therefore, studying onmechanism of rock burst is of great importance.This article is in support of Doctoral Program of Higher Specialized ResearchFund (20110143110017) and mainly analysis and research of influence on rock burstintensity under high confining pressure and low confining pressure unloading, throughhomemade machine, and400mm to600mm to1000mm large size and highstrength gypsum specimen. Then it verifies the correctness of the analysis of thelaboratory tests and the impact of stress path on gradient for rock burst by PFC2Ddiscrete element modeling software.In indoor experiment,through the different proportion of cube specimens underuniaxial compression test,it is concluded that water paste ratio is lower, the rock bursthas a propensity to rock burst, the indoor test selected0.7:1of the mixture ratio ofspecimen with medium rock burst orientation of the model. Under the effect ofgradient stress path, the high confining pressure unloading and low confining pressureunloading experiments on rock burst damage show that unloading station near surfacestrain are mutations and destruction mainly occurred near the unloading surface rockwhen burst damage happen. In the process of loading, the energy savings have aprocess before unloading,crack extension is quite slow before the confining pressureunloading. However,Low confining pressure unloading earlier than high confiningpressure unloading,the cracks expand quickly, energy release, low confining pressureunloading has more cracks before rock burst, finally which lead rock burst intensityappears in high confining pressure unloading is higher than low confining pressureunloading test, rockburst under high confining pressure unloading late at lowconfining pressure unloading. By debugging repeatedly PFC2D numerical model material mesoscopicparameters, macroscopic parameters of specimen can be obtained, which coincidedbasically with the indoor model macro parameters. According to the results of twokinds of a numerical simulation of the loading scheme ancompared with laboratorytest, the results have good consistency. Results show that high confining pressureunloading rock burst intensity is higher than low confining pressure unloading andmore sudden.The occurrence of rock burst is a process of gradual damage, and theoccurrence of rock burst is in the premise of generation of crack and its connectionBy PFC2D, analyzing the influence of rock burst under the four loading andunloading paths on the stress gradient at the top and designing seven kinds of stresspaths,analysis of and study effects of of gradient Path for rock burst strength, rockburst intensity, range of rock burst damage, and rock burst maximum tangential stress.The results of analysis are that:1) The intensity of rock burst about uniformlydistributed load is greater than gradient loading;2) With the radius of tunnelexcavation, the greater the stress gradient range is, the smaller the stress gradientslope is, the smaller initial maximum tangential stress is also,when rock burst in therock burst will happen;3) The change of the stress gradient path is of certaininfluence to the occurrence of rock burst site of unloading surface; the greater Stressgradient loading range is, the bigger the crack propagation path is, the greater thedamage range is also; And the damage area of large gradient stress range is shownas the wedge shape, however, the damage area of smaller gradient stress range isshown as bottom of the pot Shape. |
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