Tunnels and underground structures

The dominant criterion: irreversibility

On a residential building, a waterproofing mistake can be fixed from the inside. On a metro station or a cut-and-cover tunnel, access to the positive side is lost forever once backfilling is done, and stopping the service for a repair carries costs out of all proportion to the work itself.

This pushes towards redundant systems: not a single barrier, but the combination of concrete made waterproof in the mass, an active system on the positive side, and compartmentalisation that limits the extent of any defect.

Bentonite geocomposites

These are the recurring choice on base slabs and diaphragm walls. Granular sodium bentonite, enclosed between woven and non-woven geotextile, hydrates in a confined way and seals; self-anchoring structures give mechanical adhesion to the concrete poured on top, removing the cavity through which water could migrate. CE marking to EN 13491 with attestation system 2+ is the reference for public-contract supplies.

Compartmentalisation

Dividing the surface into watertight compartments, bounded by waterstops and served by injection tubes, turns a possible leak from a diffuse problem into a local, injectable one. It is a modest expense during construction and the only real insurance on a structure that will no longer be accessible.