Geotechnical competence and Eurocode 7 supervision
Eurocode 7 rests on assumptions about who does what. How geotechnical categories change the scope, why supervision of the investigation matters, and the difference between factual and interpretative reports.
Geotechnical competence under Eurocode 7 is not a badge on a letterhead. The code is written on the assumption that named people with stated skills do specific things: collect the data, interpret it, design from it, and supervise the works against it. Where a developer buys a borehole log and nothing else, most of those assumptions fail quietly, and the cost appears at foundation stage rather than at tender.
Eurocode 7, published in the UK as BS EN 1997 with its National Annex, sets out those assumptions explicitly. A second generation of the Eurocodes is being published, so check which version your specification calls up before you rely on clause references.
What the code expects of the people involved
The validity of a Eurocode 7 design rests on stated assumptions about personnel. Data required for design is collected, recorded and interpreted by appropriately qualified personnel. The structure is designed by appropriately qualified and experienced personnel. There is continuity and communication between the people gathering data, the designers and the constructors. And adequate supervision and quality control are provided on site.
Read that list as a specification for your appointment rather than as boilerplate. If the ground investigation contractor interprets their own data, and the structural engineer designs from a summary sheet, and nobody attends site during piling, three of the four assumptions have gone.
In UK practice the competence question is usually answered through the Institution of Civil Engineers register of ground engineering professionals, which grades individuals by the complexity of work they are assessed as able to lead. Ask for the name and grade of the person signing, not the firm.
Geotechnical categories and what they change
Eurocode 7 sorts work into three categories, and the category drives how much investigation and what level of person you need.
| Category | Typical work | What it demands |
|---|---|---|
| 1 | Small, simple structures, negligible ground risk | Routine methods, qualitative experience |
| 2 | Conventional structures and foundations, no exceptional risk | Quantitative data and calculation |
| 3 | Unusual or very large structures, abnormal risk, difficult ground | Specialist input, often alternative provisions |
Most housing sites sit in Category 2. What pushes a scheme into Category 3 is rarely the building. It is the ground: made ground of unknown origin, mining legacy, soluble rocks, slope instability, deep basements next to existing structures, or a site where groundwater sits above formation level.
Get the categorisation on paper early, because it determines the scope of the investigation. A Category 2 site investigated as though it were Category 1 produces a report that cannot support a design, and you pay for a second round.
Supervising the investigation itself
Supervision of the ground investigation is where money is saved and information is lost.
An investigation run without geotechnical supervision produces logs written by the driller. Those logs are usually competent descriptions of what came out of the hole, and they are not a substitute for an engineer or engineering geologist deciding, in real time, to extend a borehole through an unexpected soft layer or to take an extra undisturbed sample.
Specify who attends, how often and with what authority to vary the scope. On a Category 2 site, part time attendance at the start of each technique and at any anomaly is usually proportionate. On a Category 3 site, expect full time supervision.
Sampling standards matter as much as attendance. BS 5930 governs the investigation itself, and sampling and groundwater measurement follow the relevant ISO standards. Where samples are going for chemical testing as well as geotechnical testing, the handling requirements differ, and that is a point worth reading alongside the guidance on accredited laboratories for soil and water analysis.
Factual and interpretative reports
Eurocode 7 distinguishes the ground investigation report, which records what was found, from the geotechnical design report, which states the design values, the assumptions and the supervision requirements.
Buyers frequently conflate them. A factual report is a record: logs, test results, water strikes, laboratory certificates, a site plan of exploratory hole positions. It contains no design advice and no characteristic values. An interpretative report selects characteristic parameters, explains the ground model, identifies hazards and recommends foundation solutions.
Ask which one you are buying. A factual report priced against an interpretative scope is the most common misunderstanding in ground investigation procurement, and it surfaces when the structural engineer asks for an allowable bearing pressure that nobody has derived.
The geotechnical design report is the document that should list the construction supervision, monitoring and maintenance requirements. Those requirements then need to reach the contractor, which is a question of how the appointment is novated rather than a technical one.
Coordinating with contamination work
One set of exploratory holes should serve both the geotechnical and the geoenvironmental objectives, and the specification should say so before anyone mobilises.
The disciplines pull in different directions. Geotechnical sampling wants undisturbed samples at design depths. Contamination sampling wants shallow samples across the site footprint, in the right containers, within holding times. Ground gas monitoring wants installations left in place for a monitoring period that the programme has to accommodate.
Land contamination work is a report type where a suitably qualified and experienced person is legally expected, with investigation carried out in accordance with BS 10175. A Contaminated Land Assessment and a geotechnical assessment can share a site investigation, but they cannot share an author unless that person holds both competences.
Foundation advice at planning stage
Planning rarely requires foundation design. It does require enough ground information to show that the development is achievable and safe, and there are four situations where the case officer will ask.
- Sites in a coalfield referral area, where a coal mining risk assessment is expected.
- Sites with known instability, landslip or made ground, where ground stability policy applies.
- Basements, particularly in London boroughs that require a Basement Impact Assessment addressing hydrogeology, slope stability and effects on neighbouring structures.
- Sites with mature trees on shrinkable clay, where foundation depth affects the retention case for the trees.
A Basement Impact Assessment is the clearest example of geotechnical work that is a planning document rather than a construction one, because it addresses effects beyond the site boundary.
Checking the scope before you sign
Five questions separate a usable appointment from an expensive one.
Who, by name and register grade, will interpret the data and sign the geotechnical design report. Which geotechnical category applies and on what basis. Whether the fee covers supervision attendance, and how many visits. Whether the deliverable is factual, interpretative or both. And whether the same investigation is serving contamination objectives, with the sampling specification written accordingly.
Councils treat a Geotechnical Assessment as a document needing a suitably qualified author, and professional review is strongly advised. An AI-assisted draft can set out the structure, the policy references and the questions the assessment must answer, and it will flag missing site data rather than inventing it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.
If you need a reviewer to check and sign off a draft, the professional directory is the route.
Frequently asked questions
What is the difference between a factual and an interpretative ground report?
A factual report records what was found: borehole logs, test results, water strikes, laboratory certificates and exploratory hole positions. An interpretative report selects characteristic parameters, sets out a ground model, identifies hazards and recommends foundation solutions. Buying the first while expecting the second is the most common procurement error in ground investigation.
Which geotechnical category applies to a housing site?
Most conventional housing sites fall in Category 2, which calls for quantitative data and calculation. Category 3 is triggered by the ground rather than the building: made ground of unknown origin, mining legacy, soluble rocks, slope instability, deep basements adjoining existing structures, or groundwater above formation level. Agree the category before specifying the investigation.
Does a ground investigation need supervision on site?
Yes, in proportion to the category. Without geotechnical attendance the logs are written by the driller, which is a record rather than a decision. An engineer or engineering geologist on site can extend a hole through an unexpected soft layer or take an extra undisturbed sample. Category 3 sites usually warrant full time supervision.
Can one investigation serve both geotechnical and contamination objectives?
Yes, and it usually should, but the specification must say so before anyone mobilises. Geotechnical sampling wants undisturbed samples at design depths, while contamination sampling wants shallow samples in the right containers within holding times, and gas monitoring needs installations left in place. One investigation, two sampling regimes, written into one scope.
Is geotechnical information needed for a planning application?
Often, though rarely as foundation design. Case officers ask where the site is in a coalfield referral area, where ground instability or made ground is known, where a basement is proposed, or where mature trees on shrinkable clay affect foundation depth. Basement impact assessment is the clearest case of geotechnical work that is a planning document in its own right.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.