Stability evaluation on widening of parallel tunnels

Abstract

Widening of tunnels in urban areas, instead of building newtunnels, may become a viable solution for reducing traffic congestion. In the present study, a numerical investigation using FEM was conducted to examine the effect of tunnel widening on the stability. For the purpose, parallel tunnels were analyzed by considering four different widening types. For each case, stress and deformation behaviors of the tunnels were examined and the pillar stabilitywas evaluated.The results indicated that comparing between the tunnel widening cases with the same pillar width after widening, 5 to 20% higher crown settlement was occurred for the tunnels widened uni-laterally than those widened bi-laterally. As expected, the highest shotcrete stress was observed for the tunnels widened to have the narrowest pillar. For all four widening cases, however, the strength/stress ratios for pillar were found to have the values higher than 1.0. © 2014 Korean Geotechnical Society, Seoul, Korea.