A geotechnical engineer investigates the ground beneath a site to understand its properties and identify risks before construction begins. Their work feeds directly into the foundation design produced by the structural engineer, and into contamination and environmental assessments required by planning. Without a geotechnical report, it is impossible to confirm appropriate foundation depths, predict settlement, or satisfy mortgage lenders on brownfield and unknown-ground sites.
What they do
- Ground investigation using boreholes, trial pits and in-situ testing
- Soil and rock sampling and laboratory testing
- Foundation recommendations including depth, type and bearing capacity
- Slope stability analysis for embankments and cuttings
- Contamination assessment and ground gas monitoring
- Settlement and differential movement prediction
- Retaining structure design input
- Assessment of mining legacy, subsidence and dissolution risk
When you need one
Geotechnical engineers are needed whenever ground conditions are uncertain, planning requires investigation, or the site has a history of industrial use, mining or instability.
Typical costs (UK, 2025)
| Job type | Typical cost |
|---|---|
| Preliminary ground investigation (trial pits) | £800 - £2,500 |
| Detailed ground investigation (boreholes) | £2,000 - £8,000+ |
| Contamination assessment - Phase 1 desk study | £600 - £1,500 |
| Contamination Phase 2 physical investigation | £2,500 - £8,000+ |
| Foundation design report | £600 - £1,500 |
| Hourly rate | £90 - £160 / hr |
Investigation costs depend heavily on the number of boreholes or pits required, the depth of investigation, and the laboratory testing programme. Always obtain a scope of work before agreeing a fee.
Qualifications to look for
The standard engineering qualification for geotechnical practitioners. Requires a recognised degree, supervised experience and a professional review. Check membership at ice.org.uk.
The chartered qualification for geologists who specialise in applied and engineering geology. Particularly relevant where geological mapping, rock classification or dissolution risk is involved. Check at geolsoc.org.uk.
Relevant where geotechnical work overlaps with contamination, groundwater and flood risk. Confirms competence in environmental aspects of ground investigation.
How to find a reputable geotechnical engineer
Related Calculators
Extension Cost Calculator New Build Cost Calculator Underpinning Cost CalculatorFrequently asked questions
Do I always need a geotechnical engineer for a new build?
Not always, but lenders and building control often require a ground investigation report on unknown ground, sites with shrinkable clay, or brownfield land. Without a geotechnical report, your structural engineer cannot confirm the appropriate foundation design, and building control may refuse to approve foundations without evidence of ground conditions.
What is a Phase 1 contamination assessment?
A Phase 1 contamination assessment is a desk study that reviews historical maps, aerial photographs and environmental records to identify potential sources of contamination on or near the site. If significant risk is identified, a Phase 2 physical investigation - involving soil and groundwater sampling - is required before planning can be discharged.
How much does a ground investigation cost?
A preliminary investigation using trial pits typically costs £800-£2,500 depending on the number of pits and the laboratory testing required. A detailed investigation using boreholes - needed for larger buildings or complex ground conditions - typically costs £2,000-£8,000 or more. Contamination investigations add further cost.