Enniskillen, County Fermanagh, Northern Ireland
Introduction:
As part of a UK and Ireland ground investigation framework, we delivered a phased investigation consisting of a desk study and exploratory investigation which satisfied geotechnical design requirements and discharged Local Authority conditions to achieve planning consent. To the satisfaction of the Client, the works were delivered within the projected programme and budget.
Details:
The project involved the demolition and replacement of an existing place of worship.
A desk based review indicated no obvious former contaminative uses, however a joinery was present adjacent with associated above ground fuel tanks.
The site was indicated to be underlain by glacial soils followed by Carboniferous bedrock of the Ballyshannon Formation.
The main potential hazards included:
- Asbestos containing materials (ACM) in the existing building to be demolished and the possible cross contamination of shallow soil on-site.
- Made Ground associated with historic development.
- Potential on-site migration of contamination from the adjacent joinery.
- Volume change of fine grained glacial soils/weathered bedrock.
- Ground dissolution within the limestone bedrock, with karstic features identified in the wider area.
Investigation points were positioned across the site to obtain a general overview of the ground conditions. In addition, a targeted site investigation report was also undertaken along/near the site boundary adjacent to the joinery. The scope of works included:
- Windowless sampling at the proposed structure location to inform the foundation design;
- Shallow hand excavated trial pits to assess the contamination status of the shallow soils adjacent to the joinery.
- Dynamic cone penetrometer testing in areas of proposed car parking.
Ground conditions comprise a thin covering of Made Ground, followed by predominantly fine-grained with local coarse-grained Glacial Diamicton. A relict Topsoil is present locally.
Low levels of contamination and no asbestos was identified in the thin Made Ground identified. Low risks were considered to be posed to environmental receptors (e.g. Carboniferous Limestone aquifer). Precautionary advice was provided due to the ACM in the existing building and the proposed demolition and recommendations included the removal of any organic material during construction (including the relict Topsoil) to limit potential gas risks.
Design recommendations for shallow strip foundations, a suspended floor slab and pavement design were given with consideration requried due to the shrinkage and swelling potential of the fine grained glacial soils. A watching brief for anomolous conditions associated with ground dissolution was recommended during foundation construction.
Our investigation was sufficient to identify the key ground issues at the site.