Desk Study, Ground Investigation and Soakaway Testing, Norfolk

Desk Study, Ground Investigation and Soakaway Investigation for proposed residential development in Norfolk

Client: Strategic land development company

EMS’s geo-environmental team have recently completed an investigation of a site to address contamination, geotechnical and drainage issues.
The site is a large arable field on the outskirts of a town in Norfolk for which a residential development is proposed.

EMS produced a desk study report which included a site inspection. The report found that the risk of contamination affecting the site was generally low, but low to medium in some locations due to a former railway cutting and a former garage close to the site. An intrusive investigation was recommended to address these minor contamination issues and to provide information relating to foundation design.

The intrusive ground investigation comprised in excess of twenty trial pits excavated to approximately 3.50 m with a JCB backhoe excavator. Contamination and geotechnical samples were taken from the trial pits by the EMS geo-environmental engineer. The investigation found that the site was covered by a thin layer of topsoil followed by sandy and gravelly clay. Chalk soils were found at varying depths across the site. The investigation confirmed that the site was uncontaminated and that traditional shallow foundations would be appropriate for the proposed development. California Bearing Ratio (CBR) testing was also carried out utilising EMS’s Mexecone Penetrometer to give an early indication of likely CBR values for road pavement design.

Following the ground investigation, a five day programme of soakaway testing in full accordance with BRE365:2016 was completed. This involved testing the chalk soils for conventional soakaways and the near-surface soils to inform the design of permeable pavements. Deep and shallow tests were carried out at five locations spread across the site. The testing showed that the deep chalk soils across the site had good permeability and would be suitable for conventional soakaway drainage. The near-surface soils had variable permeability, therefore permeable pavement would not be suitable in some areas of the site.