Chadwell Road Essex Residential Development

The site investigation identified a thin layer of sandy topsoil, up to approximately 0.60m thick, overlying Boyn Hill Gravel. The Boyn Hill Gravel was found to comprise a variable mixture of clay, sand and gravel. Although clay bands were present, they were thin, infrequent and of low volume change potential, meaning the shallow soils were predominantly granular.

The ground conditions also included Thanet Sand and Chalk at greater depth. Tree influence zones covered several areas of the development, but following assessment, the clay was not considered to present a significant heave risk. This meant that a non-voided piled raft solution could be adopted.

SPEEDECK proposed a non-voided piled raft foundation solution across the three areas of the development. The solution comprised approximately 373m² of piled raft foundations, covering Plots 1-9, Plot 10 and the garage block. Rather than relying on deep trench fill foundations within the variable shallow ground, the piled raft transferred structural loads through the poorer near-surface soils to stronger bearing strata at depth. The rafts were designed with thicknesses ranging from 225mm to 300mm, providing a foundation solution tailored to the individual areas of the development.

The foundations incorporated 300mm diameter piles, generally ranging from 6.0m to 9.5m in length, with a maximum safe working load of approximately 480kN. Following the ground investigation and heave assessment, no void former was required across the scheme. Sulphate levels were also assessed as low, allowing SPEEDECK to specify DC-1 concrete for the slabs and DC-2 concrete for the piles.

By combining the piling and raft design within a single foundation solution, SPEEDECK was able to provide Mostrim Groundworks with a foundation strategy designed specifically around the site’s ground conditions rather than simply following the deeper conventional foundation approach.

SPEEDECK delivered the piling, raft slabs and underslab drainage as part of a coordinated five-week construction programme.

A lightweight piling rig was used, removing the need for an engineered piling mat. This helped keep the site cleaner and allowed the foundation sequence to progress efficiently across the three rafts.

The integrated approach meant the foundation works could be coordinated as one package, from piling through to the completed raft foundations.