Geotechnical reporting and Eurocode 7 responsibilities

Who signs a geotechnical report depends on which report you mean, because Eurocode 7 splits the work into two documents with different authors and different liabilities. The ground investigation report presents and evaluates what was found. The geotechnical design report states the design values, the assumptions and the supervision required on site. One person can write both, and on many projects one person does, but the duties are separate and a developer who does not know which they have bought will find out at building control stage.

That split is also the answer to most arguments about scope. If nobody has been appointed to produce the design report, nobody has taken responsibility for the design values, and the numbers in the investigation report are evaluations rather than instructions.

Geotechnical categories and the effort each implies

Eurocode 7 sorts structures into three geotechnical categories, and the category governs how much investigation and design effort is appropriate.

Category 1 covers small and comparatively simple structures where the risks are negligible, the ground conditions are known from comparable experience, and there is no excavation below the water table in difficult ground. Qualitative work based on experience can be enough.

Category 2 covers conventional structures and foundations with no exceptional risk or unusual ground conditions. Most housing, most commercial buildings and most retaining structures sit here. Quantitative geotechnical data and calculation are required.

Category 3 covers very large or unusual structures, structures in highly seismic or unstable ground, abnormal risks, and conditions outside the scope of the standard provisions. It calls for additional investigation, specialist analysis and, frequently, independent review.

Two practical uses for the category. It tells you whether a proposal from a ground investigation contractor is proportionate, because a category 2 site quoted as if it were category 3 is being over-investigated and a category 3 site quoted as category 2 is being under-investigated. And it tells you whether you need someone to do design at all, or only to evaluate.

The category is provisional at the outset and is meant to be reviewed once the ground is known. A site assumed to be category 2 that turns out to contain deep uncontrolled fill is category 3, and the investigation should be extended rather than the finding minimised.

Investigation, interpretation and design as separate duties

Three activities, and confusion between them causes most of the disputes.

Investigation is the physical work: boreholes, trial pits, in situ testing, sampling, laboratory testing, carried out to the relevant parts of the standards on ground investigation and site investigation practice. The output is factual data.

Interpretation is the evaluation of that data: ground model, stratigraphy, groundwater regime, derived parameter values, identification of hazards. The output is the ground investigation report.

Design is the selection of design values, the calculations for the limit states, the specification of the foundation or retaining solution, and the statement of what must be checked during construction. The output is the geotechnical design report.

The gap that opens most often is between the second and third rows. A developer commissions an investigation, receives a well written interpretative report, and assumes the foundation design is covered. It is not. The interpretative report gives parameters. Someone still has to choose the design values, apply the partial factors and specify the solution.

Who signs which part of the report

Factual data is signed by the contractor who produced it, and the accreditation of the testing laboratory matters. Ask which tests were carried out under an accredited schedule and which were not, because that distinction affects how much weight the results carry.

The interpretative report is signed by the engineer or geologist who prepared it, and it should state clearly what it is and what it is not. Good practice is an explicit statement that the report does not constitute a geotechnical design and that design values require the designer's own verification.

The design report is signed by the geotechnical designer. Where the structural engineer takes the design responsibility, the designer is that engineer, working from the interpretative report. Where a specialist takes it, the interface with the structural design has to be defined in writing, including who owns the foundation loads, the settlement limits and the construction sequence assumptions.

Ask for the signature page on all three. It is a quick way to discover that a document you thought was a design has no designer.

Chartered geologist and chartered engineer routes

Competence in this field is evidenced in a few recognised ways, and the right one depends on the task.

Chartered engineer status through the civil or structural institutions is the usual route for someone taking geotechnical design responsibility. Chartered geologist status is the usual route for ground modelling, engineering geology and interpretation. A register of ground engineering professionals administered by the civil engineering institution recognises three levels of ground engineering competence and is the clearest single indicator for a category 3 project or for an independent reviewer.

What matters practically is the match between the person and the duty. A chartered geologist is well placed to produce the ground model and less well placed to sign a retaining wall design. A chartered structural engineer may be well placed to sign the design and reliant on the geologist for the parameters. Neither is a criticism of either.

For a basement or a deep excavation the competence bar rises, and our note on basement impact assessment author competence sets out what councils in constrained urban areas expect. Where you are procuring several specialisms at once, writing a specialist survey brief covers how to scope them in one instruction.

Interfaces with the contaminated land work

Geotechnical and contamination investigation share fieldwork and diverge in everything else.

The overlap is the exploratory holes, the sampling and, to a degree, the laboratory schedule. Commissioning both from one contractor under one brief avoids paying twice for the same holes, and it produces a single set of logs that both reports refer to.

The divergence is in interpretation. A geotechnical engineer assesses strength, compressibility and groundwater. A contaminated land specialist assesses source, pathway and receptor linkages against human health and controlled waters criteria. Land contamination reporting must be carried out by suitably qualified and experienced persons working to the relevant British Standard, and that is a separate competence from geotechnical design.

Three interfaces need managing explicitly. Piling through a low permeability layer can create a pathway to groundwater, which is a contamination issue arising from a geotechnical decision. Ground gas protection measures interact with floor slab design. And any material to be reused as engineering fill has to satisfy both geotechnical suitability and the relevant waste and contamination controls. Raise all three at the brief stage, not after the Contaminated Land Assessment has been issued.

What a building control body expects

Building control looks for justification of the structural design, and for foundations that means evidence of the ground conditions and of how the design accounts for them. In practice they will want the investigation data, the derived parameters and the design calculations, and on a site with unusual conditions they may ask for the designer's credentials.

Two points to plan for. Where design responsibility is split between a specialist and the structural engineer, building control will want to see that the interfaces are covered, so a written record of who owns what saves time. And where the design relies on construction stage verification, for example inspection of formation level or of pile records, the verification regime has to be stated in the design report and then actually carried out with records kept.

Planning and building control are separate processes with separate requirements. A Geotechnical Assessment submitted to support a planning application addresses the planning issues, such as stability, land instability and the deliverability of the proposal. It does not discharge the building control duty.

Scoping an investigation that will not need repeating

Repeat investigations are common and almost always avoidable. Four things prevent them.

1. Write the brief from a desk study, so the holes target identified uncertainties rather than a standard grid.
2. Include the contamination scope in the same brief, with the same exploratory holes.
3. Specify depths against the likely foundation solutions, including the piled option, rather than to a nominal depth.
4. Install and retain monitoring wells where groundwater or ground gas could govern, because returning to the site to install them later costs more than leaving them in.

Also state in the brief who will produce the interpretative report and who will produce the design report. If the answer is that nobody has been appointed for the second, you have found the gap before it costs you.

Note that Eurocode 7 and its supporting standards are periodically revised, so confirm the current published versions and the UK National Annex before writing a specification.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.

PlanScope can draft the planning documents that accompany ground investigation evidence, and reviewers who can check and sign off a draft are listed in the professional directory. 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.