Eurocode 7 and the geotechnical report at planning stage

Planning does not ask you to design the foundations. It asks whether the ground can support the development you are proposing without unacceptable risk to the site, to neighbouring land or to controlled waters, and whether that risk can be managed by condition. Eurocode 7, the geotechnical design standard, and BS 5930, the code of practice for ground investigations, are how you answer that at a level a council and its consultants will accept.

The mistake is to commission the full design investigation before permission, or to submit nothing and hope a condition covers it.

What planning needs, and what design needs

The planning case is about suitability and deliverability. A desk study, a walkover and a preliminary risk assessment usually establish whether the ground conditions are compatible with the proposal, where the significant uncertainties lie, and what further work is required. That is enough for most applications, and the council will impose a condition requiring intrusive investigation and a remediation or foundation strategy before construction.

The design case is about numbers. Eurocode 7 sets the framework for geotechnical design, with limit state verification, partial factors applied through the UK National Annex, and two formal deliverables: the ground investigation report, which records what was found, and the geotechnical design report, which states the design values and the assumptions behind them. Those belong to the construction phase and to Building Regulations approval.

Where the two overlap is the interesting part. On sloping sites, in coalfield referral areas, over shallow mine workings, in areas of dissolution features, on made ground of unknown origin and on any scheme involving a basement, the ground question is a planning question because the development may not be deliverable at all.

Desk study and preliminary risk assessment

Start with records. The British Geological Survey holds borehole records, geological mapping and dissolution and landslide datasets. Historic Ordnance Survey editions show former ponds, pits, tanks and railway land. Coal Authority referral areas require a coal mining risk assessment, and the referral boundary is published.

A desk study that is worth reading sets out:

• The published solid and drift geology, and what it implies for bearing capacity, shrink-swell potential and groundwater.
• The site history from map regression, with every former use that could have left made ground, foundations, tanks or contamination.
• A preliminary conceptual site model identifying sources, pathways and receptors, which is also the starting point for the contamination work under BS 10175 and the land contamination assessment.
• Known mining, quarrying, landfill and dissolution risks, with the data source named.
• A statement of what remains uncertain and how the next phase will resolve it.

Councils read the uncertainty section most closely. An honest list of unknowns with a proposed scope attracts a workable condition. A desk study that declares the site suitable on no evidence attracts a request for intrusive work before determination, which costs a determination period.

Boreholes, windows and trial pits

Intrusive investigation methods are chosen for the question being asked, and BS 5930 is the reference for scope and execution.

Numbers and spacing follow from the ground model and the structure, not from a rule of thumb. What matters at planning stage is that the investigation reaches the depth of influence of the proposed foundations and any underlying hazard, and that standpipes or gas monitoring wells are installed early enough to produce a monitoring record.

Piling decisions often get made on the back of this work, and the method chosen has planning consequences of its own where neighbours are close, which is the subject of piling methods beside sensitive neighbours.

Reporting to the geotechnical design standard

A report structured to Eurocode 7 reads in a particular order, and reviewers look for the same things each time.

1. Scope, standards applied, and the National Annex version used.
2. Factual record: logs, test results, laboratory certificates, monitoring data, with the sampling and testing regime stated.
3. Interpreted ground model, with characteristic values and the basis on which they were selected.
4. Geotechnical category, and the design approach and partial factors adopted.
5. Design recommendations: bearing, settlement, slope stability, retaining structures, groundwater control.
6. Ground gas and contamination assessment, cross-referred to the separate contamination reporting rather than duplicated.
7. Residual risk and the verification required during construction.

Separate the factual from the interpretive. A council's consultant checking a basement application will want to see the raw logs and decide for themselves whether the characteristic values are defensible. Reports that present only conclusions get sent back.

Ground gas and the contamination overlap

Ground gas monitoring is where programmes go wrong. A meaningful dataset needs multiple visits spread over months, under a range of barometric pressures and including a falling-pressure event, because gas emission rates respond to pressure change. Groundwater levels need the same treatment, with winter high groundwater captured where it matters.

That is a seasonal constraint with real consequences. If the monitoring record has to start before the application is determined, the investigation has to be commissioned several months earlier than the programme assumes. If the monitoring can follow a condition, the discharge application has to be allowed for in the construction programme.

Gas protection design follows BS 8485, with the characteristic situation derived from the monitoring data. Specify nothing before the data exists. Where dewatering is contemplated, the consenting position is separate again and runs on its own timescale, as dewatering a basement excavation and the consents needed sets out.

Agreeing the scope before you go to tender

Three investigation tenders priced against three different assumptions tell you nothing. Write the specification first, and get it agreed by the structural engineer, the contamination consultant and, where the site warrants it, the council's own consultant through a pre-application enquiry.

A workable specification states the objectives, the hazards to be resolved, the methods and minimum depths, the in situ and laboratory testing schedule, the monitoring regime and its duration, the reporting standard, and who owns the data. It also states access constraints, because plant that cannot reach the back of the site is the most common cause of a part-completed investigation.

An illustrative example. A 1.2 ha former engineering works on a gentle slope, proposed for 40 dwellings with an undercroft car park. The desk study identifies made ground, a filled pond, two former tank positions and a coal referral boundary clipping the eastern edge. The planning submission goes in with the desk study, a preliminary risk assessment, a coal mining risk assessment and a scope for the intrusive phase. Permission is granted with conditions covering site investigation, remediation strategy and verification. The intrusive work and the monitoring then run alongside the condition discharge and the detailed design, rather than ahead of a decision that might never come.

A Geotechnical Assessment drafted to this structure gives the ground specialist a starting point and the council a document it recognises. Enter the postcode on PlanScope to see which reports the site's recorded constraints are likely to trigger.

This is general guidance, not legal advice. For specialist technical reports, qualified professional input may be required: ground investigation and geotechnical design must be carried out and reported by suitably qualified and experienced persons, and an AI-assisted draft is a starting point for that work rather than a substitute for it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.