RC Ground Bearing rafts

Work Type

Design and build RC ground bearing rafts, RC retaining wall alongside neighboring property, dynamically engineered 3mtr infill including installation of internal and external drainage.


Relic Homes Ltd


Aldenham Avenue, Radlet, WD7

Project Overview

SPEEDECK were approached by SAGE Design to assist with a foundation solution for the 2 proposed plots on behalf of Relic homes.

The site previously consisted of a single plot dwelling with an upper rear garden and lower level garden dropping 3mtrs down into a landscaped pit, backing onto neighbouring property.

Our client Relic Homes were building 2no bespoke 5 bed homes plus garages on behalf of private clients.

Site Review

Plot 49 (lower site)

Excavated Gerrards Cross gravel over Hertfordshire Pudding stone over Lambeth Group – predominantly sandy clay over Seaford & Newhaven chalk.

Plot 49A (upper site)

Lambeth group – predominantly very sandy silty clay with no heave potential. (based on swellage tests) over Seaford & Newhaven chalk.

Access to the site was through a single private driveway off Aldenham Avenue, which required close management with the residents as over 100 deliveries were required throughout the foundation stage of the works.


Site strip to the lower level with all soft and hard landscaping being disposed off-site. Profile formation for the base of 22mtr long retaining wall alongside the neighbour’s property which will incorporate the soffit of garage foundation at the top of the wall. Once the 2.5mtr high retaining wall was cast, engineered infill to the lower level commenced with imported stone being compacted dynamically in 300mm layers until 500mm from required formation where a non-frost susceptible stone was installed.

Our engineer specified 325mm ground bearing reinforced concrete rafts supported by dynamically compacted engineered infill on 50mm concrete working surface. By carrying out CPT probes over the footprint of the proposed new structures we were able to model the potential deflection with the rafts and schedule the steel required accordingly to ensure our design remained economical.


SPEEDECK were appointed as principal contractor for the groundworks and installation of design and build foundation scheme.

Contracted works was completed within 9 weeks (1 week ahead of programme). Our scope of works on the project covered; Site clearance and enabling works, construction of temporary haul road, design and build reinforced concrete retaining wall, engineered infill to lower level, under plot drainage and services, design and installed reinforced concrete foundations, external drainage and soakaways, stoning up of scaffold bases and patio/pathway areas.

Advantages of Our System

SPEEDECK provided a whole site solution from demolition of exiting plot and handing over 2 no structural foundations with all site drainage installed. One contractor, one point of contact cost effectively.