THE PROBLEM

In order to minimise import of fill and maximise the use of site won material it was necessary to utilise excavated weak sandstone from the Hindhead Tunnel in the reinforced soil walls on the project. This material was outside the normal Highways Agency specification for reinforced soil walls.

THE SOLUTION

The Tensartech TW3 system which includes Tensar uniaxial polymer geogrids as reinforcement, allowed the use of the excavated fill. In addition it allowed the use of Yorkstone facing blocks which were chosen to blend in with the surrounding area of outstanding natural beauty.

PROJECT DESCRIPTION

The A3 Hindhead project consists of a new 6.5km road with a 1.8km tunnel to take traffic away from the Devils Punchbowl area of outstanding natural beauty and site of special scientific interest. On either side of the tunnel there are extensive earthworks which include the construction of seven underpasses and retaining walls using reinforced soil amounting to approximately 2000m² of wall face. For environmental reasons it was necessary to utilise as much site won fill as possible in these structures, including some of the sands and weak sandstone of the Hythe Beds excavated from the tunnel. Tensar International were selected by the ECI Contractor Balfour Beatty to design and supply the Tensartech TW3 system for these structures.

The fill material was classified as 7J and the properties defined by the Project Consultant Mott MacDonald. The Tensartech TW3 system is a modular block system with an attractive split face which can be constructed at a face angle of 90 degrees, as was required on this project. The dry laid blocks, Tensar uniaxial polymer geogrids and connectors are the subject of a British Board of Agrément Certificate for Roads and Bridges for use in reinforced soil bridge abutments and retaining walls with a 120 year design life. For this project a special Yorkstone colour was selected to blend in sympathetically with the surrounding area.

Balfour Beatty Structures Team Leader Jeremy Bayne-Powell said that “the Tensartech TW3 system has proved to be both economical and quick to build and has also provided attractive structures which blend in well with the surroundings.‘‘