Abstract

The divergence section of a double-deck tunnel can be divided into a ‘wideningpre-divergence section’, a large cross-section with a cap shape and a ‘post-divergencesection’ where the separation between the main and the branch tunnel is made. Sincethe cross-section of the widening pre-divergence section is considerably larger thanthat of the post-divergence section, the influence of excavation due to the differentsizes and shapes in the cross-section should be considered in the examination of thetunnel stability. In this study, the effect of the preceding excavation, that is theexcavation of the widening pre-divergence section, on excavation stability of thepost-divergence section was examined by varying the excavation methods and benchlengths through 3D finite element analysis. The results showed that although theeffects of the excavation methods and the bench lengths are not significant on thevariation of principal stresses, the preceding excavation causes a relatively largevariation on the stresses which may have an impact on the stability of thepost-divergence section from the comparison of Stress-Strength Ratio (SSR) betweenthe cases with and without the consideration of the preceding excavation effect by 2Dfinite element analysis.