Betws‑y‑Coed bridge foundations: cofferdam design and access lessons for engineers
Reviewed by Joe Ashwell

First reported on The Construction Index
30 Second Briefing
Foundations are now complete for a new 50‑metre shared-use suspension bridge replacing the historic Sappers’ Bridge over the River Conwy at Betws‑y‑Coed, built under a £3m Conwy County Borough Council contract with MWT Civil Engineering. Deep abutment excavations for mass concrete plinths were formed in a high water table using a sheet‑piled cofferdam with interlocking Larssen piles, welded corners, Groundforce Mega Brace beams and three MP50 hydraulic struts. Two ICE8SG side‑grip hammers installed piles over 6m long, while an unusual sheet‑piled ramp provided plant access without cranes beside the 14th‑century St Michael’s Church.
Technical Brief
- Mass concrete plinths at each abutment are designed to resist main suspension cable anchor loads.
- Live road and protected trees adjacent to the cofferdam constrained plant positioning and excavation footprint.
- Interlocking Larssen sheet piles with welded corners were specified to minimise water ingress from the high water table.
- Two ICE8SG side‑grip hammers were selected over standard EMVs to safely handle >6 m piles.
- Cofferdam support used Groundforce Mega Brace modular beams with three MP50 hydraulic struts spanning excavation walls.
- An inclined, sheet‑piled access ramp into the excavation removed reliance on cranes for plant access, reducing lifting risk.
Our Take
The 2021 safety-driven closure of Sappers’ Bridge fits with a cluster of Safety-tagged UK pieces in our coverage where local authorities, including Conwy County Borough Council, are being forced into accelerated replacement of century-old crossings once inspections reveal latent defects, rather than relying on incremental strengthening.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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