| Necessity analysis of pre-improvement support system on large section underground structures | |
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 - Scale Effect Analysis - Optimization of Pre-improvement Support System - Spatial Distribution Effect on LUS and Risk AnalysisNowdays, the space required underground is rapidly incresing due to various purposes such as underground gymnasiums, LPG storage, large underground shopping malls etc. To construct large underground spaces safely, it is indeed asking the tunnel engineer "How can we support the large excavation surfaces with no collapse and no failure?" Pre-improvement support should be carried out to prevent the excessive vertical deformation at the ground surface and tunnel crown, to induce the long-term arching effect for stabilization, to prevent collapse, and to improve the stand-up time on large underground excavation. Various pre-improvement auxiliary techniques for tunneling are used to reinforce the ground and improve the stability of the tunnel face. The selection and the construction of an auxiliary technique depend on the geologic characteristics such as the water table condition or rock mass quality. Especially. In particular , the umbrella arch method (Kim et al. 1998) is the most frequently used auxiliary technique for highly fractured rock or shallow depth tunneling. Furthermore, its application study and effectiveness analysis and the qualitative and systematic design sequences have been verified by many researchers focused on the general small scale of tunnel diameter. However, the behavior characteristics of large underground excavation are somewhat different compare to a tunnel of general scale. A necessity analysis was performed focused on the large tunnel excavation in this study, and the effectiveness analysis on three design parameters of the umbrella arch method have been performed simultaneously using the 3D finite element method. To suggest an optimized pre-improvement support system, the effect of spatial distribution and risk analysis according to the scale effect would be investigated based on this research. |