Land quality – managing ground conditions

Also see:
BS EN 1997-2

4.1.5Basic Investigation (sites where hazards are not identified or suspected)

Where hazards are not suspected, a Basic Investigation of the site, including geotechnical and contamination investigations, shall be carried out by a suitable person and recorded to the satisfaction of NHBC.

The Basic Investigation aims to provide assurance for all sites, regardless of how free of hazards they may appear, and forms the minimum requirement for a site investigation.

The number and depth of trial pits should be located so they are representative of the site and will depend upon the:

  • proposed development
  • nature of the site
  • inconsistency of the soil and geology across the site.

Trial pits should be located outside the proposed foundation area, and generally be a minimum of 3m deep. The distance from the edge of the foundation should not be less than the depth of the trial pit. Where trial pits do not provide sufficient information, boreholes will be necessary.

Basic geotechnical and contamination investigations should be conducted and include:

  • physical tests, such as plasticity index tests, to support the results of the Initial Assessment
  • a basic contamination investigation based on sampling and testing of soil taken from trial pits during the geotechnical investigation.

During the excavation of the trial pits, the use of sight and smell may help to identify certain contaminants.

If the Basic Investigation reveals the presence of geotechnical and/or contamination hazards, or has not addressed all of the original objectives, or where there is any doubt about the condition of the ground, further Detailed Investigation should be conducted.