RSA Geotechnics initially carried out a ground investigation at the Enviro21 Queensway South site in St Leonards-on-Sea, Hastings, East Sussex, for Coastal Innovation Ltd in May 2008.
The investigation was required to provide information on the geology beneath the smaller of the two fields forming the Queensway South site, which had not been covered by earlier investigations. The investigation comprised a series of light-cable percussion boreholes down the sloping profile of the site. The scheme’s designers required the information to design foundation and retaining wall structures.
This information was critical, as the site was underlain by Wadhurst Clay, which contained irregular sandstone layers supplying groundwater to the adjacent Marline Valley Woods, a site of special scientific interest (SSSI) and local nature reserve (LNR). The planning conditions for the development stipulated that the cut and fill earthworks and foundation excavations must not encounter the sandstone, as this would potentially affect the quality and pH of the groundwater, adversely affecting the flora and fauna of the SSSI.
Three of the four boreholes were completed successfully; however the borehole at the top of the slope encountered a sandstone layer that was not able to be penetrated by cable percussion techniques. Subsequently a rotary borehole was drilled at the same location to prove the thickness of the sandstone layer. The results of the investigation were provided as a factual report for use by the designers.
RSA Geotechnics were instructed by Coastal Innovation to carry out the independent geological supervision of phase 1 of the Environ21 Queensway South Scheme, as part of a joint section 106 agreement between Coastal Innovation and Hastings Borough Council. Phase 1 of the scheme comprised the construction of an innovation exchange, three commercial office/manufacturing units, retaining structures, car parks and the site road for the innovation park.
RSA Geotechnics were tasked with supervising all excavations on site to ensure compliance with the planning conditions, stopping work if sandstone was encountered or was likely to be encountered in any of the excavations and reporting any breaches of the sandstone horizon to the client and council so that remedial action could be undertaken and the affected parts of the scheme redesigned. The geological supervision was carried out from January 2009 to January 2010, when all excavations for phase 1, covered by the section 106 agreement, were completed.