Kilnwood Vale, Crawley

The Kilnwood Vale site consists of about 132 ha of land, around 42 ha of which comprises land previously developed for inert waste management activities. Planning permission has been obtained for 2,500 dwellings, new access points, a neighbourhood centre, retail space, a public house, an elderly care facility, a nursery and 2-3 form entry primary school. CampbellReith has provided the geotechnical, earthworks and remedial design to de-risk the landfill area and transform this into a development ready platform. In addition, the practice has provided the design of roads, drainage and earthworks at both the masterplan and detailed design level. CampbellReith’s civil engineers produced the drainage and earthworks masterplan and thereafter the detailed design of the primary road and drainage infrastructure.  It was necessary to interface the civil design with the performance criteria for the geotechnical treatment of the landfill so as to address the residual settlements that were anticipated. Extensive regulatory liaison was held with the adopting authorities in order to agree the preferred design approach. Regarding the environmental issues, CampbellReith modified the remediation strategy in order to utilise forensic soil descriptions to allow the soils excavated from former landfill to be screened and classified for reuse. Upon completion of works, surface gas emission scans, flux box monitoring and traditional borehole monitoring was implemented in order to allow the assessment of residual passive ground gas designs for the proposed housing.  The approach allowed the site to be redeveloped despite previously having elevated ground gas concentrations without the need for extensive post construction gas monitoring. CampbellReith designed and supervised the geotechnical treatment for the former landfill area of the site.  Up to 15m of residual fill material was treated via the excavation, screening and selective placement of the upper layers combined with a surcharge operation for the deeper layers of fill.  As part of the works, a low permeability mineral clay liner was constructed in order to control infiltration.  The works were monitoring during the surcharge period via the use of settlement plates, extensiometers, vibrating wire piezometers and surface settlement stations. Extensive use was made of the civil 3d package PDS and GIS in the development of the remediation design and the earthworks model in order to provide a sustainable earthworks balance. GIS was used to visualize ground gas results and aid the Land Quality team with a remediation strategy; to show cut-and-fill areas and to aid the placement of Drum Test locations. Services: Civil, Environmental, Geotechnical, Highways & Transport, GIS & GISSMo Sectors: Regeneration, Residential, Retail