Pavement Rehabilitation: Norton, Suffolk

RSA Geotechnics was requested by Babergh District Council to carry out a ground investigation to investigate the condition of Prospect Road, Norton and to provide advice on repair of the road. This investigation was undertaken in conjunction with Suffolk Pavement Evaluation (SPE) who provided detailed remedial design options.

Prospect Road, is a cul-de-sac that comprises a straight length of road approximately 135m long, joined to an oval section which measured approximately 100m from end to end, and 35m across. The road is bordered by residential properties and the oval section surrounded a grassed area.

The road was generally in a poor state and remedial options were required by the client to keep the road in a safe and serviceable condition.

The straight section and two short spurs, approximately 25m in length at each end of the oval part of Prospect Road, were constructed of concrete which had been surface dressed. Along the transverse concrete joints the surface dressing was occasionally absent and some vegetation growth was present in the joint depressions. Occasional longitudinal and diagonal cracks were evident on the surface, which based on visual inspection appeared to be in the surface material only. There were occasional other areas where the surface dressing was absent and the concrete was exposed, and there were occasional patch repairs.

The oval part of Prospect Road was of flexible construction and had also been surface dressed.  There were occasional patches where the surfacing had deteriorated and begun to spall and there were also occasional patch repairs.

RSA Geotechnics carried out coring of the road pavement at four locations to determine the road construction and dynamic cone penetrometer (DCP) tests through the base of the core holes to provide an indication of the in-situ California Bearing Ratio (CBR) value.

The cores revealed that the concrete pavement construction was approximately 300mm thick and surfaced dressed as previously described. At the core locations there was no sub-base present and the concrete rested directly on formation soil. The sub-grade comprised firm, brown/grey, silty clay (Lowestoft Formation glacial till) of intermediate plasticity with flint gravel, chalk gravel and silt/sand pockets.

The fully flexible section of Prospect Road comprised a 40mm thick wearing course with a 120mm thick binder layer below. Below the bound layers there was between 140mm and 170mm of orange/brown, slightly silty sand/flint gravel sub-base, with the Lowestoft Formation glacial till present below the sub-base.

Remedial options were provided by SPE in accompanying report which included plane out and hot rolled asphalt (HRA) inlay, or use of a thin surface course system (TSCS).