Mapei has provided several waterproofing system solutions for the new Silvertown Tunnel, opened this spring. The new tunnel, which links Silvertown to the Greenwich Peninsula in east London, was delivered by Riverlinx CJV, the construction joint venture comprised of Ferrovial, BAM, and SK Ecoplant, on behalf of Transport for London (TfL) and Riverlinx. The Mapei specification included waterproofing membranes, reinjectable hose, and acrylic injection gel systems.

Spanning 1.4km, the new Silvertown Tunnel runs under the River Thames and includes dedicated bus lanes. It comprises open and closed-cut and cover approach sections, portals, and a twin-bored main central section. Modelling shows that it will help to reduce congestion, deliver faster journey times, help manage overall air quality, and promote better cross-river public transport.

Technical collaboration and a spirit of partnering between Mapei’s technical team and the stakeholders enabled all design detailing and installation challenges to be met. These included critical movement joints between the bored tunnel, portal, and road slab sections; interfaces and continuity of all waterproofing systems; penetration detailing; and measures to protect working areas and water run-off prior to open works.

During the project, Mapei was asked for an urgent solution to provide additional external waterproofing for a large corrugated galvanized steel tube-type attenuation tank, before it was buried in backfill. In response, Mapeplan TU S – a single-layer synthetic waterproofing membrane with an orange signal layer – was applied as a fluid barrier and was also used in the portal, rotation chamber, and closed-cut and cover tunnels on the Greenwich side of the tunnel.

To seal the tunnel against leakage paths, several kilometres of Idrostop Multi 11 reinjectable hose system were installed in the joints of the open and closed-cut and cover tunnel sections and portals. Mapegel UTT low-viscosity acrylic injection gel system was used to seal the tunnel against leakage paths. Installation and concreting were conducted several months prior to injection, and the hose and connections were encased in concrete.

Mapeproof AL AP pre-applied, fully bonded, and self-adhering HDPE waterproofing membrane was selected as the primary external waterproofing for the open-cut tunnel approaches, enabling the slab and walls to be poured directly against the membrane. Mapeproof AL AP is cold applied with completely watertight seams, before installing steel reinforcement and pouring concrete, and does not require a protective layer. After the concrete has been poured, it becomes fully bonded, preventing water from migrating laterally between the foundation structure and the membrane. Other Mapei products specified included Mapeplan Waterstop BR 400 PVC waterstop and Idrostop 10 hydrophilic expanding rubber profiles.

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