Meadow Lane, Suffolk Residential Development

SPEEDECK’s Geotechnical review identified Made Ground over the Lowestoft Formation and Crag Group, over Chalk at depth. Groundwater was encountered in only one borehole, at approximately 14.5m, meaning it was sufficiently deep not to govern the foundation design.

Atterberg limit and desiccation testing indicated non-plastic to medium volume change potential within the upper 3m, with no meaningful evidence of local desiccation. These findings provided the technical basis for challenging the assumption that a voided foundation was required simply because of the Tree Influence Zone.

Following review of the ground investigation and geotechnical data, SPEEDECK proposed a non-voided piled raft solution. The approach was developed in liaison with the warranty provider to obtain the relevant approval for the proposed foundation strategy.

By using the site-specific geotechnical evidence rather than defaulting to a voided solution, the design avoided the additional excavation and void-forming requirements that would otherwise have been introduced.

The foundation design incorporated 300mm diameter piles, designed in accordance with Eurocode 7 Design Approach 1, Combination 2, with pile lengths ranging from 6.0m to 12.0m. The reinforced concrete rafts were designed using RC35 concrete, with raft thicknesses ranging from 225mm to 300mm. Across the development, approximately 403m² of structural foundations were proposed.

Design coordination also identified a potential clash between a manhole and the underside of the raft. This was resolved during the design process by lowering the manholes by approximately 100mm, avoiding an issue during construction.

SPEEDECK delivered the piling and raft slabs as a single substructure package, incorporating underslab drainage and services within the same works.

A lightweight piling rig was selected for the project, removing the need for an engineered granular piling mat. One area of the site had returned below the usual bearing threshold during tender-stage assessment. Rather than automatically introducing additional ground improvement, plate-bearing CBR testing was undertaken ahead of mobilisation to confirm whether the existing ground could safely support the piling rig.

The testing confirmed the ground’s suitability, allowing the lightweight rig to be used without the need for an engineered piling platform. The piling and structural foundation works were delivered within a six-week construction programme, from commencement of piling through to handback at structural slab level.