BS 5930 and Eurocode 7 (BS EN 1997-1:2004) set the standard for geotechnical investigation in the UK, but applying them on the West Sussex coastal plain demands local geological understanding you cannot get from a textbook. Bognor Regis sits on a mix of Brickearth, raised beach deposits, and the underlying London Clay Formation, with groundwater often just a metre or two below ground level. We regularly see sites where perfectly adequate-looking topsoil masks variable compressible layers beneath, something that only a properly designed soil mechanics study will pick up. The town's ongoing regeneration, from the Arun District Council’s local plan allocations to individual self-build plots, means more projects are pushing into marginal ground where desktop studies alone are not enough. Our laboratory combines index testing, strength measurement, and consolidation analysis to give you a ground model you can actually design to, rather than a set of numbers with no interpretation. When shallow foundations look marginal, we often recommend supplementing the investigation with test pits to visually log the transition between the drift deposits and the weathered bedrock, which can vary sharply across a single site.
On Bognor's coastal plain, the real risk is not the London Clay at depth but the variable Brickearth and raised beach deposits in the upper three metres.
Site-specific factors
Our investigation teams in Bognor Regis typically deploy a tracked dynamic sampling rig for the upper drift deposits, switching to cable-tool or rotary coring when they hit the London Clay or need to prove the top of the Chalk bedrock. The most common call we get starts with a site that looks straightforward: a level plot on Brickearth, maybe an existing bungalow to replace. The owner has seen the ground and assumes it is stable, so they skip straight to architectural drawings. What they do not see is the perched water table that forms after heavy autumn rain, saturating the silt and turning it into a near-liquid slurry under foundation loads. We have pulled cores where the undrained shear strength dropped below 30 kPa just 1.8 metres down, values that would not support a conventional strip footing without Improvement. A properly scoped soil mechanics study identifies that condition before the digger arrives, giving the structural engineer the data to specify either a deepened foundation, a raft, or a ground treatment strategy. The alternative is retrospective underpinning, and in a coastal town like this, that gets expensive fast.
Relevant standards
BS 5930:2015+A1:2020 – Code of practice for ground investigations, BS EN 1997-1:2004 (Eurocode 7) – Geotechnical design, general rules, BS 1377-2:1990 – Methods of test for soils for civil engineering purposes: classification tests, BS 1377-5:1990 – Compressibility, permeability and durability tests, BS 1377-7:1990 – Shear strength tests (total stress)
Common questions
How much does a soil mechanics study cost for a typical house extension in Bognor Regis?
For a single-storey extension or a replacement dwelling on a standard plot, a soil mechanics study in Bognor Regis generally falls in the range of £2,840 to £3,750, depending on access, depth required, and the number of laboratory tests specified. Sites with difficult access, suspected contamination, or deeper foundations will push toward the upper end. We can provide a fixed-price proposal after a brief site walkover.
Do I really need a soil mechanics study for a small residential project, or is a basic trial pit enough?
It depends on the ground. In parts of Bognor Regis where the Brickearth is thin and consistent, a trial pit with hand vane tests may satisfy building control. However, on sites closer to the coast, near watercourses, or where the London Clay is shallow, the variability in the upper drift demands proper lab testing to quantify settlement and bearing capacity. A full soil mechanics study gives your structural engineer the parameters they need to justify the foundation design, which often saves money on overdesigned footings.
What's the difference between a soil mechanics study and a standard site investigation?
A standard site investigation tells you what the ground looks like. A soil mechanics study measures how it will behave under load: strength, compressibility, permeability, and volume change potential. It turns field observations into numerical design parameters that an engineer can use directly in Eurocode 7 calculations. In our experience, this is particularly important in Bognor Regis where the Brickearth can exhibit collapse settlement that a visual log alone will not predict.
How long does the laboratory testing phase take?
Classification tests such as moisture content, Atterberg limits, and particle size distribution can be turned around in five to seven working days. Consolidation and triaxial tests take longer, typically two to three weeks, because the oedometer requires incremental loading stages and the triaxial needs saturation and consolidation phases before shearing. We schedule the testing to match your design programme and can issue interim factual data ahead of the full interpretive report.
Are you accredited for geotechnical laboratory testing in the UK?
Yes. Our laboratory operates under a quality management system aligned with ISO 17025, and all testing is performed to the relevant parts of BS 1377. Calibration of load cells, displacement transducers, and balances is traceable to UKAS-accredited calibration laboratories, which gives your building control officer and warranty provider the assurance they need.
