Ground conditions and foundations assessment

Certain conditions cause most of the trouble and each needs handling specifically. Shrinkable clay swells and shrinks with moisture and the seasons, and near trees it can move enough to crack a building, so foundations are deepened or designed to accommodate the movement, informed by the guidance on building near trees. Made ground and fill are unpredictable and often need piling through to competent strata. Sloping sites bring lateral stability and differential foundation depths. A high or variable water table brings buoyancy, softening and construction difficulty. Old mine workings, soluble ground and contaminated fill each add their own constraints.

The reason these matter is differential movement. A building can settle a surprising amount uniformly and suffer little, but it cracks when one part settles more than another, which is exactly what happens when foundations bridge from firm ground onto soft, or sit at different depths, or span a filled area next to natural ground. We look for these transitions across the plot and design the foundations so the movement is even, or so the structure is stiff enough to ride over the variation, rather than discovering the change halfway through the dig.

For a new build we set the foundation strategy from the ground investigation and the loads, coordinate with the ground investigation contractor on what testing is needed, and design the foundations and any below-ground structure to suit. For existing buildings the assessment answers a different question: whether the current foundations can take a new load, an extra storey, an extension or a change of use, which means establishing what the existing foundations are and what they sit on, usually through trial pits, before deciding if they can be reused or need to be extended.

The deliverable is a clear basis for the foundation design: the ground model, the bearing capacity and settlement we have adopted, the foundation type and the reasoning, in a form your engineer, architect or Building Control can rely on. Where we are doing the full structural design we carry the ground assessment straight through into the foundation and superstructure. Ground conditions and the codes applied to them are consistent across the UK under Eurocode 7 with national parameters, and we work with clients across both, delivering assessments remotely and arranging site work by region.