| Summary: | 碩士 === 中原大學 === 土木工程研究所 === 86 === Rock-burst is a drastic failure phenomenon that always occurs in underground excavations, especially for those with great depth. Because the rock fragments fly from the excavation walls due to the rapid release of energy, rock-burst endangers the construction facility and personnel on the site. In Taiwan, more proposed tunnels will pass through the high mountain regions (like Central Mtn.), and it is inevitable to encounter the severe rock-burst problems. In the field, the intact rock mass before failure may be regarded as continuous, however, when it starts to crack and produces flying rock fragments due to excavation unloading, a discontinuous behavior prevails. The Discontinuous Deformation Analysis (DDA) developed by Dr. Shi will be used to study such a problem in this thesis. The initial program of DDA combined with the Artificial Joint Concept (AJC) which first cuts a continuous domain into sub-blocks by artificial joints and then re-glue them together by assigning T0, coh., fric., is adopted to simulate the progressive fracturing of a rock mass under external loading. In the numerical study of uni-axial compression test by strain-controlled loading on one specimen composed of intact rock and another with one inclined discontinuity, the DDA results are well compatible with the theoretical solution. Additionally, in the study for the specimens cut by a certain pattern of artificial joints, it is found that the strain loading rate, the strength (friction angle and cohesion) and inclination of artificial joints affects the stress-strain relationship computed by DDA, to some extent. In the study of machine stiffness effect, DDA yields the results comparable to that defined by the traditional theory, i.e., when machine stiffness is greater than the post-peak stiffness of rock specimen, a complete stress-strain curve can be obtained; otherwise the rock specimen suddenly breaks near the peak strength. It is a great challenge in engineering practice to precisely predict the rock-burst behavior in tunnels. The DDA combined with AJC is still used in the thesis to provide a means to conduct such a task, in which a normalized kinetic energy index (E*) is defined to quantify the fracturing rate of a rock mass, and further to represent a potential index of rock- burst. The simulation results indicate that the time-history curves of E* and the survival number of cemented contacts could be adopted to point-out the initiation time of rock-burst and energy release level. Moreover, in the such a system reveals its lower potential of rock-burst. The method- ology to predict the rock-burst potential proposed in the thesis is actually on its premature stage, and it is suggested in the near future to perform more parametric study, to modify computation algorithms and include field data for enhancing its capability.
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