SPEEDECK proposed a CFA piled raft foundation as the most technically suitable and cost-effective solution for the site’s complex conditions. The design integrated the piling and raft slab within a single substructure package, eliminating multiple trade interfaces and reducing coordination risks. Full heave protection was adopted beneath Blocks 2, 3 and 4, with partial protection beneath Block 1, ensuring long-term performance under variable tree influence zones.
Concept Design
Design Engineering
The foundation was designed as a 300 mm reinforced concrete raft, incorporating 225 mm RDS voidformers where required for heave mitigation. Piles were 300 mm diameter CFA, designed to Eurocode and warranty standards, achieving a maximum safe working load of 480 kN with pile lengths ranging from 6.0 m to 17.0 m. The total raft slab area across the four blocks measured 1,657 m², delivering a single, durable substructure system that optimised both material efficiency and long-term stability.
Construction
SPEEDECK delivered the piling and raft construction as one integrated scope of substructure works, simplifying sequencing and improving safety and quality control. The approach streamlined installation of underslab drainage and services while minimising contaminated soil removal. The resulting substructure handed back to slab level, providing a predictable and level platform ready for superstructure works to progress without delay.
