In tunnelling, it is essential to provide adequate water drainage both during and after the construction phase. Depending on the prevailing mountain and water conditions, both the upper part of the tunnel arch and the tunnel base are affected by fissure, stratum, and seepage water. The long-term stability and permanent usability of a tunnel depend on whether the inner shell and base are reliably protected against water ingress and consequent frost damage. It is imperative to collect the surface and seepage water over a wide area between the inner and the outer shell of the tunnel, both in the upper and in the lower parts of the tunnel, and to remove it through carefully designed drainage and seepage layers. This applies particularly for efficient tunnelling methods using water impermeable concrete which must not come into contact with seepage water during the curing process nor be loaded hydrostatically.
The various DELTA dimpled sheetings offer rational and dependable solutions for coping with water in all kinds of tunnel construction projects according to the existing mountain and water conditions. While the studs pointing outwards, that is against the ground or rock or a stabilizing and filtering shotcrete layer, a complete conduit system is provided by the spaces between the studs allowing the water to flow unimpeded to the drainage system. From the very start, water is prevented from building up against the waterproofing layer which can be fixed directly to the dimpled sheeting by appropriate fixing means. When water impervious concrete is used, DELTA dimpled sheeting serves as a permanent formwork. The seepage water is held back during the curing phase.