Harbourside House, Eastbourne

Ground investigation revealed variable and locally deep Made Ground across the site, particularly on the upper platform. Beneath this layer were beach deposits consisting predominantly of dense granular soils, transitioning into soft clay layers and deeper Weald Clay at greater depth.

Given the mixed ground conditions and structural requirements of the building, a piled raft foundation solution was selected to provide a robust and efficient foundation system capable of transferring loads safely through the variable strata.

Additional considerations included:

• Areas of clay influenced by vegetation, specifically blackthorn, requiring heave protection.
• High flood risk, potentially affecting final site levels and the ground model.
• CS3 ground gas classification, requiring appropriate gas protection and ventilation measures.
• High UXO (Unexploded Ordnance) risk, requiring careful site management during groundworks.

The engineering solution incorporated several measures to mitigate the complex site conditions and ensure compliance with environmental and structural requirements.

A HVCP voidformer system was introduced in a small area of the north-east section of the site where clay soils and tree influence posed a potential heave risk.

To address the CS3 gas conditions, the foundation design incorporated an integrated gas protection system, including gas strips and a gas membrane, ensuring the building met the required safety and regulatory standards.

The overall design approach allowed the team to balance structural performance with buildability, ensuring the foundation system could be delivered efficiently while accommodating drainage and service installations between key construction stages.

SPEEDECK delivered a fully integrated foundation package, coordinating multiple workstreams to maintain programme efficiency and quality control throughout construction.

The scope of works included:

• Piling works
• Concrete blinding
• Installation of under-slab drainage and services
• Gas protection measures including gas strips and membrane
• Formwork and reinforcement installation
• Lift pit base construction
• Coordination with warranty provider inspections
• Concrete pours for the piled raft slab
• Final strike and site clearance

Despite the challenging ground conditions and logistical constraints, the 1,304m² piled raft slab was successfully completed within the nine-week programme.