Case Studies

School Extension, Billingshurst, West Sussex

By reviewing an existing risk assessment, Ashdown Site Investigation has realised significant cost savings for this project which comprised several extensions and alterations to the existing school buildings.

A contamination risk assessment for the development prepared by other geoenvironmental consultants included some limited ground gas monitoring, and solely on the basis of the maximum concentration of carbon dioxide recorded within the one of the installed standpipes, concluded that a significant risk was posed by ground gases and that gas protection measures would be required within all new parts of the school building.  The risk assessment also tacitly inferred a risk was posed to the existing structures which do not incorporate gas protection measures. Similarly the geotechnical advice given within the report prepared by the geoenvironmental consultants, specifically relating to the bearing capacity of the soils, was questioned by the structural engineers responsible for the design of the extensions, who deemed the advice to be unnecessarily conservative.

Ashdown Site Investigation undertook a detailed desk study including a review of historical mapping and other environmental data for the site, and was able to conclude that no potential sources of ground gas existed either beneath or in the vicinity of the site. We also undertook some further monitoring of the gas wells previously installed and this confirmed that no significant concentrations of ground gases or flow rates were present. Based on this we were able to review the risk assessment report and conclude that no gas protection measures were required within the proposed development or existing buildings.  The reviewed risk assessment was accepted by the regulators resulting in significant cost savings to the client.

Similarly Ashdown Site Investigation conducted additional geotechnical ground investigation works at the site and, based on the results obtained and detailed calculations, advised that a higher bearing capacity for the soils could be safely assumed.  This resulted in significant savings to the foundation construction costs.