1 The Waterproofing System
The waterproofing system in tunnels caters for three important functions:
It separates the subsequent bearing structure from the excavation support in order to avoid constraining forces
It protects the inner shell from possible aggressive underground water
It protects the traffic area from underground water
A tunnel can either be sealed all-around with a waterproofing membrane (Fig. 1) or devised as a water impermeable concrete structure from the very outset. Table 1 contains a list of the most important waterproofing systems for the closed construction method.