Shoreham Flood Defence - Reach W5 Case Study

SHOREHAM FLOOD DEFENCE 8km of coastal defences at Shoreham, Sussex, UK, required 700m of sheet piling through an existing flood embankment in a very restricted space. The ground consists of a made ground embankment constructed on a rock/rubble construction platform; alluvial deposits; spit gravel and; chalk. Assumption at design stage was for a self-supporting piling rig to push piles to depth. The piling contractor raised the risk that obstructions in the embankment, particularly at shallow depths, prevented progress. A risk reduction meeting was convened, with the client, designer, contractor and piling sub-contractor, which concluded mitigation measures needed to be clearly understood to reduce delays and uncertainty. A piling protocol was developed and agreed by all parties which included a flow diagram of mitigations and diagrams of acceptable pile length configurations. Three separate pile criteria needed to be met; long enough for: the piling rig reaction piles; wall stability; and to control seepage rates during a flood. Not meeting the first of these would stop piling, the biggest cost risk, whereas the others permitted remedial works after completing the piling. Mitigations were required for short driven depths, though no significant delays occurred and no disputes on where cost for delays were borne.