RSA Geotechnics recently undertook a survey of the embankments and cuttings (highway geotechnical assets) along the A130 from the A12 interchange at Chelmsford to the Rayleigh Spur 14km to the south. This stretch of the A130 is maintained by County Route under the terms of a design, build, finance, and operate (DBFO) contract on behalf of Essex County Council.
The road comprises two sections north and south of a grade separated junction, the A132 Rettendon Turnpike. The northern section was completed in 2002 and the southern section followed in 2003. The road includes fifteen bridges, one subway and five culverts, and crosses the River Crouch, Sandon Brook, the A127 Southend Arterial Road, the A132 at Rettendon and two railway lines. The A130 runs either in cutting or on embankment for most of its length.
According to the published geological information the general area is shown to be underlain by a discontinuous superficial layer of river deposits (comprising River Terrace Deposits, Alluvium and Tidal Flat Deposits), glacial deposits and head deposits, underlain by the Thames Group (comprising the Claygate Member and London Clay).
The geotechnical inspection comprised three stages:
– An inspection of earthworks drawings and initial drive-by to identify locations of the cuttings and embankments along the route of the A130. The drawings were inspected and the majority of the route was shown to comprise either cuttings or embankments which included slopes greater than 2.5m in height. This was confirmed by the drive-by survey. Although some sections were at grade it was concluded that the site inspection would be a walked survey for the whole length of the A130 in both the southbound and northbound directions.
– A site survey on foot to identify signs of incipient slope failure or slope faces that had failed prior to the survey. The length of the A130 from Chelmsford (A12) to the Rayleigh Spur and including the slip roads was walked, both in the southbound and northbound directions. Generally the toe, crest and face of each embankment or cutting encountered were surveyed, where accessible.
– A review of the information gathered from the site survey to provide an assessment of identified incipient slope instability indicators and associated inspection and maintenance requirements.
The results of the survey were assessed to provide a risk rating for any identified defects, to enable the managing agent to determine future maintenance requirements. The rating was based on categories of repair or reinstatement.