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Durability of precast concrete tunnel segments

M. Bakhshi & V. Nasri
AECOM, New York, USA

ABSTRACT: 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 to move on from prescriptive approach and embrace performance-based approaches for
durability design of tunnel segmental lining is demonstrated and future studies are discussed.