Ground investigation and factual report
Fieldwork such as boreholes, trial pits and testing to find out what the ground is made of, with a factual record of the results.
About this service
A ground investigation finds out what is actually under your site. It can include boreholes drilled to depth, hand-dug or machine-excavated trial pits, window sampling with a small rig, and tests in the ground and in the laboratory. The factual report is the record of all of it: what was found at each hole, at what depth, how the soil behaved and what the test results showed. It is the evidence base for safe and economical foundation design.
On London sites the typical sequence is topsoil and made ground over London Clay, sometimes with gravels, sands or alluvium depending on the area. The details matter. Made ground can be a metre or several metres deep. Clay can be desiccated by trees to a surprising depth. Groundwater can sit perched in gravels above the clay. A designer working without this information has to be cautious, and caution usually means deeper, more expensive foundations.
We plan the investigation around your scheme, supervise the fieldwork and compile the logs and test data into a clear factual report. It records observations and results only, without interpretation, which keeps the evidence clean for whoever designs from it. Fees start from £2,000 + VAT. Once issued, the report can feed directly into a geotechnical design report or foundation design.
When you need it
- You need ground data for foundation or basement design
- Building Control or an insurer needs ground information
- The site has clay, made ground or trees
What's included
- Planning and supervising the fieldwork
- Boreholes, trial pits or window samples as needed
- In-situ and laboratory testing
- Logs and test results
How it works
- Scope the investigationUsing any desk study and the proposed design, we decide hole types, locations, depths and the in-situ and laboratory tests needed, then confirm the fixed fee in writing.
- Clear and prepareWe check buried service records, agree access and protection for gardens and floors, and plan around neighbours, parking and any tree root protection areas before the rig arrives.
- FieldworkBoreholes, window samples or trial pits are excavated and logged, with samples taken and tests such as standard penetration or hand shear vane carried out as the holes advance.
- Laboratory testingSamples go for testing, which can include moisture content, plasticity for shrink-swell potential, strength, sulphate and pH for concrete specification, and contamination screening where needed.
- Factual reportWe compile exploratory hole logs, a location plan, groundwater observations, photographs and all test results into a factual report ready for the design team and Building Control.
What you receive
Factual versus interpretive: what this report does and does not do
A factual report states what was found. It does not tell you what foundation to build. That separation is deliberate, because it lets different engineers rely on the same data with confidence. If you need recommendations, design parameters and a view on construction risks, the next step is a geotechnical design report, which interprets these results. On many small schemes, a structural engineer can go straight from good factual data to a foundation design.
Access is the practical challenge in London. Rear gardens reached only through the house limit the size of rig, which in turn limits depth. Window sampling rigs can pass through a standard doorway and reach useful depths in clay, while full cable percussion boreholes need wider access. Monitoring standpipes are often installed so groundwater can be read again after the fieldwork. Our basement guide explains why groundwater readings matter so much for basements.
Frequently asked questions
How deep should boreholes be for a house in London?
It depends on the foundation type and loads. For a typical extension, holes a few metres deep are often enough to confirm the clay and any root-affected zone. Piled foundations and basements need much deeper holes, often well beyond the proposed founding level. The scope is set by the design, which is why a desk study or clear brief comes first.
What tests are done in a ground investigation?
Common tests include in-situ strength tests as the hole is dug, and laboratory tests for moisture content, plasticity (which shows shrink-swell potential in clay), undrained shear strength, and sulphate and pH to choose the right concrete. Contamination and gas testing are added where the site history or a planning condition calls for them.
Can a ground investigation be done in a back garden with no side access?
Usually yes. Small tracked window sampling rigs and hand-held equipment can be carried or driven through a house with floor protection in place. They reach useful depths in London Clay for most residential work. Very deep holes for piles or large basements may need a bigger rig, which can be harder to get into a terraced garden.
Does a factual report include foundation recommendations?
No. A factual report records the logs, test results and groundwater observations without interpretation. Foundation recommendations and design parameters come in a separate geotechnical design report, or within your structural engineer's foundation design. Keeping the two apart means anyone using the data can see exactly what was measured.