Abstract:

Based on the design concept of NATM in mountainous tunnelling, the fact that concrete linings are usually cast after ground convergence under the effect of primary supports is widely recognized. Therefore, concrete linings, which concern no stability function, could be none reinforced. However, in Taiwan, it is usually considered that concrete linings would still sustain partial forces from surrounding ground and groundwater. There are many cases which concrete lining are designed with ground loadings 25%~40% of that in primary supports. In undrained tunnels under high overburden and groundwater table, the estimated external water pressure is also deducted based on full groundwater pressure. While tunnel linings are mainly resisted axial compression forces, whether designed with reinforcement or not, they can provide quite sufficient safety factors. Because none reinforced ones are easily cracked, spalled and fell suddenly, concrete linings still to be reinforced. This paper, refers to many design cases and codes in Taiwan, tries to study the design issues on concrete lining and rebar allocation.

Key words: tunnel  , concrete linings  , reinforcement of linings