What is an Intrusive Ground Investigation?
An intrusive ground investigation is undertaken when a Preliminary Risk Assessment (PRA) identifies uncertainties that require direct testing of ground conditions.
Its purpose is to confirm the geotechnical properties of the soil and rock, determine the presence of contamination, understand the ground gas regime and provide the information required to produce a Phase 2 Environmental Ground Investigation Report.
All investigations follow the guidance set out in British standards.
What does an Intrusive Ground Investigation involve?
Each investigation is designed specifically for the site, taking into account:
- Proposed development
- Contaminated land and geotechnical risks identified in the PRA
- Programme requirements
- Budget
- Access and physical constraints
The scope is tailored to ensure the investigation delivers the information necessary for planning, design and regulatory compliance.
What can I expect from a Ground Investigation?
Typical exploratory methods include:
- Trial pits: Often completed with a wheeled or tracked excavator and used to obtain shallow samples and expose ground conditions.
- Dynamic sample boreholes: Suitable for sampling soils and installing gas and groundwater monitoring wells.
- Cable percussion boreholes: Used to investigate soils to significant depths and to identify rockhead.
- Rotary core boreholes: Used where characterisation of bedrock is required, especially in areas affected by historical mining. Rotary coring provides high‑quality samples suitable for geotechnical design.
Samples collected during the investigation are laboratory tested for chemical and geotechnical parameters in accordance with British Standard, MCERTS and UKAS requirements.
Additional investigation for higher‑risk sites
- Former coal mining areas: Deeper rotary core boreholes may be necessary to characterise coal seams, assess ground stability and determine whether grouting or other mitigation is required. Accurate assessment can often avoid unnecessary ground treatment, reducing project costs.
- Sites influenced by landfill: Extended ground gas monitoring or continuous monitoring may be required to inform a detailed Ground Gas Risk Assessment
How long does it take?
Timescales depend on site size, complexity and access but typically:
- Intrusive fieldwork: up to one week for most projects, and rarely more than two weeks
- Ground gas and groundwater monitoring: undertaken after installation of monitoring wells
The required monitoring duration will be recommended in the Phase 1 Desk Study and refined in the Phase 2 Environmental Ground Investigation Report.
Monitoring frequency is matched to the anticipated gas regime and regulatory expectations.
