The geotechnical adviser role under Eurocode 7
BS EN 1997 requires geotechnical data to be interpreted by suitably qualified people and recorded in a design report. This sets out the adviser role, the categories, and what a reviewer should check.
Eurocode 7 does not let ground investigation be a commodity. BS EN 1997 requires that geotechnical data are collected, recorded and interpreted by suitably qualified and experienced people, and that the assumptions, data, methods and results of the design are recorded in a Geotechnical Design Report. Somebody has to own that. In UK practice that person is the geotechnical adviser, and the role starts before the first borehole is sunk.
For anyone reviewing ground reports submitted with planning applications, the useful question is not whether the numbers look right. It is whether the investigation was scoped by someone competent to scope it.
What the code asks of the adviser
Eurocode 7 is in two parts. BS EN 1997-1 covers geotechnical design, and BS EN 1997-2 covers ground investigation and testing, with the UK National Annex setting nationally determined parameters. Read alongside BS 5930, the code of practice for ground investigations, they describe a process rather than a document.
The adviser's work is to define what the ground risk actually is, specify an investigation proportionate to that risk, supervise or review the fieldwork, interpret the results, and then take responsibility for the design parameters that come out of it. Interpretation is the part that cannot be delegated to a driller or to a laboratory.
The Institution of Civil Engineers maintains a register of ground engineering professionals with adviser, specialist and professional grades, which gives the word adviser a defined meaning rather than a marketing one. Where a council or a reviewer questions competence, that register is a straightforward answer.
The reporting stages and what each contains
Three documents, three different purposes, and mixing them is the most common fault in submitted reports.
- Desk study and preliminary risk assessment. Published geology, historical maps, mining and quarrying records, groundwater and hydrogeology, previous investigations, a site walkover, and a conceptual model of the ground. This is where the risk is first described.
- Ground investigation report. The factual record of what was done and what was found, including borehole and trial pit logs, in situ testing, groundwater monitoring and laboratory results. Facts only.
- Geotechnical design report. The interpretation: characteristic values, design parameters, foundation options, settlement estimates, slope stability, and the residual risks with the assumptions each conclusion rests on.
A reviewer should be able to trace a design parameter back through the interpretative report to a specific test result in the factual report. Where that chain breaks, the parameter is an opinion rather than a derived value, which may still be reasonable but should be labelled as such.
Geotechnical categories and the effort each implies
Eurocode 7 sets three categories, and the category drives the investigation rather than the other way round.
| Category | Typical case | Investigation implied |
|---|---|---|
| 1 | Small, simple structures with negligible risk, on known ground | Desk study and walkover, limited or no intrusive work |
| 2 | Conventional structures and foundations with no exceptional risk | Routine intrusive investigation and standard laboratory testing |
| 3 | Unusual or very large structures, abnormal ground risk, difficult conditions | Specialist investigation, advanced testing, often instrumentation and monitoring |
The categorisation is a judgement made at the start and revisited as data arrives. A site that looks like Category 2 on a geological map can become Category 3 when the first borehole finds made ground to 6 metres over a former watercourse.
Most disputes on planning applications come from a Category 1 approach applied to a Category 2 site, usually because the fee was set before the risk was understood.
Where ground risk becomes a planning issue
Ground conditions enter the planning system in specific ways rather than generally. National policy expects sites to be suitable for their proposed use, taking account of ground conditions and land instability, and the local planning authority will consult where there is a known constraint.
The recurring triggers are mining legacy in coalfield referral areas, historic quarrying and landfill, natural cavities such as chalk dissolution and gypsum karst, unstable slopes and landslip, shrink-swell clays near trees, and made ground of unknown origin. Basement schemes bring their own set, which is why many London boroughs require a specific assessment.
A Geotechnical Assessment prepared for planning is usually a scoping and risk document rather than a design. Say so in it. Councils are not asking for a foundation design at outline stage, and presenting one invites questions you do not need.
The relationship with contamination work
Geotechnical and contamination investigations share boreholes and rarely share objectives. One is asking whether the ground can carry the load. The other is asking whether the ground presents a risk to human health, controlled waters, property or ecosystems under the source-pathway-receptor model.
Combining the fieldwork saves money and creates two traps. Sampling depths and intervals suited to a geotechnical question often miss the contamination question, particularly where shallow made ground is the concern. And geotechnical sampling methods can cross-contaminate between strata in a way that a contamination assessment cannot accept.
Scope both at the same time, then let each discipline specify its own sampling. A contaminated land assessment follows BS 10175 and the land contamination risk management approach, and its reporting stages run in parallel with the geotechnical ones rather than inside them.
Reviewing a factual report against an interpretative one
Reviewers develop a short list of checks that catch most problems.
- Do the borehole positions match the proposed structure, or were they placed where the rig could reach
- Is the depth of investigation appropriate to the influenced zone below the foundations, rather than to a round number
- Were groundwater levels monitored over time, or read once on the day
- Are the logs signed by a named logger, and does the description follow the standard
- Does the interpretation acknowledge what was not found, including boreholes abandoned on obstruction
- Are characteristic values derived with a stated method rather than taken as the mean of everything
Where you are signing off someone else's work, the scope of your review matters as much as its content. Our note on what a reviewer actually takes on covers the liability position, and when a council can reject a report because of its author covers the competence question from the authority's side.
Where a condition secures the rest of the work
Full intrusive investigation before a decision is often unreasonable, particularly on occupied sites or where demolition has to happen first. Planning conditions are the usual answer, and the Planning Practice Guidance tests for conditions apply as they do anywhere else.
A workable condition sequence asks for a written scheme of investigation approved before work starts, the investigation and interpretative report submitted before a defined stage, any remediation or foundation design approved before construction of that element, and a verification report before occupation. Each step needs a trigger point that a compliance officer can identify on site.
What does not work is a condition requiring the development to be built on adequate foundations. Everyone agrees with it and nobody can enforce it.
Anyone signing a geotechnical design report is taking professional responsibility for it, and AI-assisted drafting does not change that. A draft can assemble the desk study sources, structure the report and flag missing data, and a qualified geotechnical adviser still has to scope the investigation, interpret the results and sign. Reviewers listed in the professional directory work on that basis.
This is general guidance, not legal advice. For specialist technical reports, qualified professional input may be required.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What is a geotechnical adviser?
The suitably qualified and experienced person who owns the geotechnical elements of a project: defining the ground risk, scoping the investigation, interpreting the results and taking responsibility for the design parameters. The Institution of Civil Engineers maintains a register of ground engineering professionals with adviser, specialist and professional grades, which gives the term a defined meaning.
What is the difference between a factual and an interpretative report?
A ground investigation report records what was done and found, including logs, in situ testing, groundwater monitoring and laboratory results. A geotechnical design report interprets that data into characteristic values, design parameters, foundation options and residual risks. A reviewer should be able to trace any parameter in the second back to a result in the first.
Which geotechnical category applies to a housing scheme?
Conventional housing on known ground with no exceptional risk usually sits in Category 2 under Eurocode 7, implying routine intrusive investigation and standard laboratory testing. The categorisation is revisited as data arrives, so a site that looks straightforward on a geological map can move to Category 3 when unexpected made ground or cavities are found.
Can geotechnical and contamination investigations share boreholes?
The fieldwork can be combined, but each discipline should specify its own sampling. Depths and intervals chosen for foundation design often miss shallow made ground that matters for contamination, and some geotechnical sampling methods risk cross-contaminating strata. Scope both at the same time rather than fitting one inside the other.
Can ground investigation be left to a planning condition?
Often yes, particularly on occupied sites or where demolition must happen first. A workable sequence approves a written scheme of investigation before work starts, then the interpretative report, then any remediation or foundation design, then a verification report before occupation. Each step needs a trigger point a compliance officer can identify on site.
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.