The Taiwan High Speed Rail (THSR) runs through several hilly areas in the northwestern island of Taiwan and there are therefore quite many tunnels constructed along the alignment. Special considerations are required for the design of these tunnels due to the face of soil-like rock strata, low overburden and underpassing the existing freeway with cover as thin as 9 m. The frequently used numerical-statistical classification methods like Bienawski's RMR-system or NGI's Q-system are not applicable for these tunnels. Considerations are also given to auxiliary measures, special portal design criteria for THSR, and effects of asymmetrical loads and earthquake loads. Various monitoring systems were then adopted to verify the initial design parameters and assumptions. The results reveal that the deformation and convergence of tunnel linings are significantly affected by the asymmetrical loads due to inclined topograpy, unfavorable bedding conditions and the poor strength of rocks.
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