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Ground Investigation Techniques – Trial Pits

Ground Investigation Techniques

Ground investigation techniques vary depending on the objectives of the investigation, the strata, and logistical factors such as access.

To assist with understanding what factors contribute to the decision on which technique to use, we have prepared a briefing note on the use of trial pits. Further techniques will be discussed, so keep an eye open for them!

Trial Pits

Summary: An excellent technique for achieving coverage to a depth of around 3m. Larger excavators can go deeper, a smaller machine is more manoeuvrable. Also used for excavating soakaway test pits.

Equipment: An excavator, may be a mini-digger, JCB 3CX or tracked excavator, depending on the ground conditions.

Time: Usually relatively rapid to deploy, as the equipment isn’t particularly specialist.

Costs: Relatively modest costs, requiring a skilled operator and machine hire.

Depth: Up to 5m deep, though normally 2m to 3m.

Coverage: Good site coverage in a day with perhaps up to 5 to 8 locations (depending on machine, ground conditions and site access).

Constraints: The excavations can be disruptive, especially if specialist reinstatement is required. Groundwater and ground gas monitoring installation not possible.

Best used when: Shallow contamination is possible with deep contamination unlikely. Often used to delineate area of contaminant impact. Good for geotechnical assessment of soils to get bulk samples for testing. Required when undertaking soakaway testing to BRE 365 specification. Particularly low cost option if the client has an excavator on site.

agb Environmental has a team of geo-environmental (contaminated land) and geotechnical specialists that can assist with ground investigations and assessments for development projects. To discuss what ground investigation technique may be suitable for your development, call Simon Pike (Principal Consultant) on 01638 663226 (Newmarket office) or email

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