| Summary: | 碩士 === 國立臺北科技大學 === 土木與防災研究所 === 96 === Because of the high geologic structure changeability in Taiwan, some underground excavating difficulties such as meeting the fissuring zone, jointed rock mass and fault may raise frequently. The mechanical tunnel excavation, therefore, becomes important for concerning its advantages of automatic efficiency and construction safety. However, the mechanism of cutting process or so-called contact mechanics is not quite clear so far. To evaluate the cutting efficiency in the viewpoint of force and energy required to break rock, this paper hence presents the mechanical cutting effect of doubled-indenters on indentation-typed excavation by varying the space between indenter to indenter, . Meanwhile, coupled nondestructive techniques of acoustic emission (AE) as well as electronic speckle pattern interferometry (ESPI) are synchronized to monitor the evolution of fracture automatically during the normal wedge indentation tests in rock-like, quasi-brittle material.
By controlling the feedback signals of the crack opening displacement (COD) in a closed-loop hydraulic loading system, the entire loading curve can then be carried out in cement mortar. The experimental results show the microscopic evolution of ductile failure followed by brittle fracture in real-time, whole-field, high resolution from ESPI images corresponding to the locations of microseismic sources from AE. Furthermore, both the displacement continuity and displacement discontinuity, which are not identical to pre- and post-peak, can then be identified. In other words, both (1). the development of plastic zone and localization of the microcracking growth at the stage of ductile failure, and (2). the onset of crack evolved from the localization and crack propagation at the stage of brittle failure can be examined respectively. Note that the programming to synchronize both data of ESPI and AE is written in LabView 8.0 software in the laboratory. This is the first automatic synchronization of coupled ESPI and AE nondestructive techniques.
Finally, this study summarizes the value of critical space ( ), critical elastoplastic interface, and crack initiation/propagation experimentally, which are reasonable and agreeable by comparing with numerical simulation of coupled distinct element (PFC2D) and finite element method (FLAC).
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