Proximity to sea defences
Despite the tunnel’s relatively recent construction, neither the local authority, nor the engineer of record, nor the utility company responsible for its operation had any record of its location and design. Extensive investigations were carried out to locate the tunnel but did not succeed. Eventually, MHA designed a balance raft foundation to replicate existing pressures on the tunnel and convinced United Utilities to accept this approach. In this way the development could proceed despite the uncertainty.
The soft fill behind the sea defence walls, on which the building was to be founded, needed to be improved by vibro-compaction to provide adequate foundation capacity.