Hochtief (UK) Construction Ltd & Anor v Atkins Ltd

A professional designer responsible for structural fill and associated drainage must design the works as an integrated system, including the consequences of design changes and interfaces with other elements. Where a design introduces an impermeable membrane over collapse-susceptible chalk fill, adequate sub-surface drainage is required to prevent water accumulating and causing collapse settlement. A contractor remains responsible for workmanship matters within its control, including carrying out specialist grouting so that a watertight seal is achieved. The court may distinguish design defects from construction defects by analysing the contractual allocation of responsibility, the design documents, expert evidence and the demonstrated cause of the damage.

The claimants, acting as a joint venture principal contractor, engaged the defendant to provide the civil and structural design for a bridge and an underpass forming part of the East Kent Access Road project. They claimed damages for remedial works following settlement of the bridge approaches and water leakage at the underpass.

The court had to determine the scope of the defendant’s design responsibility, whether the bridge design adequately addressed drainage of water collecting above an HDPE membrane over lightweight fill, whether the resulting settlement was caused by design or workmanship, and whether the underpass leakage resulted from inadequate waterproofing design or defective grouting and failure to remove anti-drag system sheets.

1. Bridge design responsibility. The subcontract made the defendant responsible for the detailed structural design, including the lightweight fill behind the abutments and wing walls and any necessary drainage of that structural fill. The exclusion of highway design and associated drainage did not remove responsibility for drainage forming part of the bridge’s civil and structural design. The defendant also had to consider the effect of its design on interfaces with Jacobs’ highway and drainage design.
2. Bridge breach and causation. The final design introduced an HDPE membrane over EPC blocks, laid to fall towards the general embankment fill. It provided no adequate drainage system to carry water away from the membrane ends and prevent penetration into chalk fill. The risk of collapse compression of chalk fill on inundation was recognised and should have been addressed. The resulting saturated, very soft chalk, settlement data, rainfall correlation and cessation of differential settlement after drainage works established that excessive water penetration caused the undue differential settlement. The design was therefore inadequate, negligent and in breach of contract.
3. The joint venture’s departures from the design, including the use of chalk fill in some areas and shortening of parts of the membrane, could explain local softening but did not account for the wider carriageway depressions. The remedial drainage works were reasonable, proportionate and necessary. The claimants were entitled to recover £802,475.35 for the bridge works.
4. Underpass. The defendant’s design required the 100mm gap between the headwall beam and deck to be filled with non-shrink grout. The court rejected the theory that relative deflection caused cracking. Although the design did not expressly require removal of the anti-drag system sheets, the joint venture should have recognised that their removal was necessary to permit full grout penetration and a watertight seal. The grouting was a specialist workmanship operation, and the joint venture carried it out at its own risk without raising practicability concerns. The leakage was caused by poor workmanship, not defective design. The underpass claim was dismissed.