Our environmental and geotechnical consultants in our Leeds office have completed many Phase 1 and Phase 2 site investigations within the Yorkshire area. An example of a contract which has been recently completed is summarised below.
Geo-Environmental and Shallow Mining Investigation – New Primary School Site, Leeds
The Land Consultancy Limited was commissioned to complete a Phase 1 desk study, a Phase 2 geotechnical and environmental and a shallow mining investigtation at the site of a primary school located within the Sheepcar district of Leeds. The existing school was to be replaced with a new school building located within a different area of the site.
A Phase 1 desk study indicated that the area of the new school had been previously developed out with terraced housing and a vicarage. Landfilling was identified in the vicinity of the site. Previous site investigation work which had taken place at the site indicated the presence of ashy fill material and shallow rock. Based off geological map evidence, the site was considered to be at moderate risk of being affected by shallow coal mining activities. A preliminary conceptual site model completed for the school, indicated that end users could be at risk from any Made Ground present and from landfill type gases; the development was also identified to be at risk from deep Made Ground and shallow mining.
To address the findings of the preliminary conceptual site model, a site investigation involving the formation of windowless sampling boreholes (with in-situ testing – SPTs) and rotary drilling was undertaken. Soils recovered from the boreholes were logged to BS5930 1999 (A2) and samples were taken for chemical and geotechnical testing. Selected boreholes were installed for gas and groundwater level monitoring purposes. Several rotary holes were advanced to depths of 40m to check for shallow coal seams/workings; the windowless sampling boreholes were advanced to maximum depths of around 5.50m. Gas monitoring was undertaken on 6no. occasions over a two month period.
As elevated levels of PAH were recorded from the Made Ground, a 'clean' capping layer was advised to be installed into areas of landscaping to prevent end users from coming into contact with this material. Elevated carbon dioxide concentrations were recorded during the gas monitoring period and therefore, a gas protection membrane was advised to be installed into the floorslab of the new school building.
Piled foundations were recommended to support the new school building as deep Made Ground and very weak Alluvial soils were encountered to approx. 2-4m depth. No shallow coal seams were encountered within the rotary drill holes. Therefore, the drilling and grouting up of shallow workings was not necessary to protect the new school from ground subsidence related to the collapse of shallow workings.