| Summary: | 博士 === 國立臺灣科技大學 === 營建工程系 === 98 === Redistribution of stress and displacement will occur during excavation of underground tunnels. The most critical excavation cycles during tunneling and monitoring were found by numerical analysis, which are called the “key cycles” in this research. A tunneling of horseshoe shaped 8m diameter tunnel was simulated in rock with three different rock mass rating (RMR) of 70,30and 12, three different lateral pressure cofficient (K) of 0.5, 1.0 and 2.0, and three different overburden depth (H) of 10, 40 and 300m. The key cycles were determined based on the calculated vertical stress and settlement redistribution during tunneling. Key cycles are reasonably proposed at the tunnel working face within 3 rounds fore and aft of the monitoring station according to the numerical results. The redistribution of three-dimension (3D) principal stress variation of stress path and safety assessment for tunneling are also investigated in this study. Numerical simulations of tunneling were performed, leading to integration of principal stress space with Mohr-Coulomb failure criterion. Different rounds have different three-dimensional redistributed stress within their individual deviatoric planes. These planes can’t be superimposed, making their comparison difficult. However, deviatoric planes representing rounds can be combined one normalized plane whereupon the stress path is plotted, allowing comparison with the cycles. A way creating the normalized deviatoric plane, with stress path therein representing the cycles, is proposed and demonstrated. This way clearly delivers the 3D redistributed stress path into a 2D tunneling chart and enables to assess the tunneling safety.
Predictable formulae based on the calculated vertical stress redistribution and settlement of roof during tunneling are proposed. The height, between the inflection point of vertical stress redistribution curve and tunnel roof during tunneling, may be a good index related to early development of ground arch and Terzaghi’s rock loads. Tunneling behavior of pillar near the intersection are also analyzed and some conclusions are proposed.
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