ENKAGRID TRC AND ROADMESH® USED TO REINFORCE ASPHALT PAVEMENT
Oxfordshire County Council Highways has embarked on a major reconstruction of the A4144 Abingdon road in Oxford, one of the main arterial roads leading from the city centre. A substantial section is to be replaced, incorporating pavement reinforcement materials from Maccaferri Ltd, specialists in retaining structures, soil reinforcement, erosion protection, basal platforms and pavements.
Running from Oxford City Centre to the southern bypass, the Abingdon road is an old road and, because of heavy traffic and poor ground conditions, the surface no longer meets the demands of present and future traffic loadings. A decision has been taken to reconstruct a two kilometre stretch of the roadway and, in the first trial phase, a length of 350 metres covering the section from Step Ground bridge to Vicarage road was completed this summer.
The Council’s engineering Babtie Group was responsible for the design and specification of the new road pavement, with term contractor Isis Accord completing the construction. Eric Imeson, Resident Engineer at Babtie asked Maccaferri’s pavement specialist to put forward a design for a pavement with a projected lifespan of at least 15 years.
Working to a minimal depth construction of 500mm below existing levels to avoid damage to existing shallow services, Maccaferri proposed an inlay reconstruction including Colbond Enkagrid TRC 30 at formation level with Maccaferri Roadmesh laid as deep as possible within the bituminous levels. This combination of products would provide the required design strength despite the limited construction depth and low bearing capacity foundation.
The Abingdon road lies over drained flood plains close to the River Thames. The natural ground beneath the road construction consists of alluvial silts and soft clays with extremely low CBR values. The northern section of Abingdon road is built over the Grandpont Causeway which was constructed in the 11th Century over the marshy flood plain. Other sections of the road have been widened and improved over a considerable time span so the makeup of the existing carriageway is very variable. The presence at very shallow depths of utility mains and services and the Norman Causeway scheduled monument limit the overall thickness of pavement reconstruction.
During reconstruction, material was excavated to a depth of 500mm and a reinforced foundation laid including Enkagrid TRC, enabling the roadbase thickness to be reduced to meet design constraints without compromising pavement strength. A high modulus multifunctional geogrid composite, Enkagrid TRC combines reinforcement, separation and filtration in a single easy to install material.
Maccaferri Roadmesh Type L was laid deep in the asphalt layer, providing maximum structural benefit. A double-twist wire mesh incorporating transversally reinforced steel wires, its antireflective cracking properties will help to prevent ruts and other damage to the road surface.
The work was completed over a period of eight weeks during the summer holidays. Ease and speed of construction was a key element in the design process as it was not possible to close the road. Undertaken in four segments, the work was finished on schedule with minimum disruption to residents.
Maccaferri Ltd specialises in the supply of gabions, geotextiles, geogrids and geomats. In addition to a full range of products for retaining structures, soil reinforcement and erosion protection, the company offers an in-house design and consultancy service.