Road Improvement: Norman Road, Belvedere, Kent

The project comprised the improvement of a poor quality private road to bring it up to a standard appropriate for adoption by the local authority, Bexley Borough Council.

RSA Geotechnics were employed as geotechnical sub-consultant to Waterman Boreham and were appointed to carry out the ground investigation, provide geotechnical design, check and approve the specialist contractor designs and supervise and monitor the earthworks construction aspects of the project.

The new road was designed and constructed as a 7.3m wide carriageway with a 1.8m cycleway. The project involved the backfilling of an existing ditch and the excavation of a new watercourse. Increases in vertical stress caused by the new road and backfilled ditch presented particularly difficult settlement risks because of the 8 to 10m of highly compressible alluvial materials. RSA Geotechnics proposed a ground improvement method called deep dry soil mixing (DDSM) which involved adding cement to the alluvial soils in-situ to increase the strength and reduce the compressibility of the soft soils.

RSA Geotechnics were employed to check the design and construction of the DDSM and the lime/cement stabilised capping. This involved monitoring and evaluating in-situ testing of the DDSM columns and the in-situ density testing of the stabilised capping layer.

RSA Geotechnics prepared a closeout report for presentation to the local planning authority checking engineers to show that the specialised geotechnical processes had been installed in accordance with the specification and would achieve the required settlement tolerances.