Durability Design of Segmental Linings for Intended Service Life of Tunnels

In one-pass lining systems, the durability of tunnel structure is directly related to durability of concrete segments acting as both the initial support and the tunnel final lining. In this paper, most-frequent degradation mechanisms of concrete linings are discussed including chloride- and carbonation- induced corrosions, sulfate, acid and freeze-and-thaw attacks, and alkali-aggregate reactions. Mitigation method for each specific degradation mechanism is explained. A durability factor specific to railway and subway tunnel known as stray current corrosion is presented. Mitigation methods for this specific corrosion together with coupling effects with other conventional damage mechanisms are explained. Prescriptive approaches for durability design based on major codes and standards are explained and comparison is made between these methods. Exposure classes as the main inputs to the prescriptive approaches are elaborated and requirements specified by the codes and standards are presented and analyzed. The need for moving from prescriptive approach to performance-based for tunnel segmental lining is demonstrated and future studies are discussed