On the Pont Briwet scheme, HOCHTIEF replaced an ageing timber viaduct with a new concrete structure across the Dwyryd estuary in North Wales. The new viaduct provides a two-lane highway as well as a crossing for the railway line, which is carried on a separate deck capable of increased line speeds.

Key features:

  • 6 span, 18m wide, 130m long concrete viaduct
  • 1.5km bi-directional railway track
  • 2km 2 lane of highway
  • Walkway and cycleway
  • New 2 car station
  • Demolition
  • Environmental mitigation measures.

To minimise disruption to the travelling public, we divided the project into two phases, reopening the railway line before the road was completed. The new bridge has six spans, built using reinforced concrete piles and piers, pre-stressed concrete beams and a reinforced concrete deck, and posed unique engineering challenges due to its location in a tidal estuary in a sensitive area and Site of Special Scientific Interest (SSSI).

We maximised offsite prefabrication to reduce the amount of work carried out over the estuary and maintain rail and road operations. Concrete deck beams, crossheads and parapets were all precast offsite to increase quality, save time and minimise the health, safety and environmental risks of working over water.

We designed the 22t crossheads as precast shell units, allowing us to install them quickly with minimal in situ concrete pouring, and we altered their design so that deck beams could be placed directly into cut outs without further support, simplifying the construction process.

The scheme achieved CEEQUAL Very Good and our innovative use of precast concrete sections led it to win the ICE Wales Cymru Innovation Award 2016, as well as a Concrete Society Award 2016.