Hazeley Road Residential Development

Following review of the proposed development layout and geotechnical conditions, we recommended a CFA piled reinforced concrete raft foundation system incorporating reinforced concrete retaining walls up to 3 metres in height for both residential plots and associated garages.

This integrated approach combined piling, retaining structures and reinforced raft construction into a coordinated substructure package. By transferring building loads through piles into suitable bearing strata while creating stable terrace platforms across the site, the system provided a practical alternative to traditional foundation methods.

Compared with conventional pile-and-ground-beam construction, the piled raft solution simplified sequencing, reduced excavation requirements and minimised muck away, resulting in a more efficient construction programme.

Site investigations identified highly variable topsoil across the development, consisting predominantly of organic gravelly silt. Beneath the topsoil, Head Deposits were encountered, comprising firm to very stiff gravelly clay, silty gravel and slightly sandy gravelly silt. These materials overlay the Seaford Chalk Formation, consisting primarily of stiff, slightly gravelly silty chalk.

The variability of the near-surface strata, combined with the significant site level changes, reinforced the need for a foundation solution capable of transferring structural loads reliably into competent bearing strata while minimising construction risk.

The engineered substructure solution incorporated 225mm reinforced concrete piled raft slabs for the residential dwellings, with 300mm thick reinforced concrete slabs supporting the garage structures where increased structural demands existed.

The development required approximately 2,002m² of structural foundations delivered across 16 piled raft foundations supporting 22 residential units and their associated garages. The foundation system was designed using SPEEDECK’s established residential design methodology and achieved maximum safe working loads of approximately 210kN. Pile lengths varied across the site to suit both the underlying ground conditions and individual structural loading requirements.

To further enhance the long-term performance of the development, an RIW waterproofing membrane was installed beneath the foundation system. This provides protection against water ingress, dampness and potentially harmful ground gases, helping to ensure a dry and durable structure throughout the building’s lifespan.

The substructure works were delivered as a coordinated package across an 18-week construction programme. Integrating the piling, retaining walls and reinforced raft slab installation reduced on-site complexity and improved programme certainty.

The elimination of traditional mats reduced material requirements and site movements, while the raft foundation design allowed drainage and service installations to be coordinated efficiently beneath the slabs. The resulting foundation platform provided a stable and reliable base for the superstructure works across all plots.