Brief Description

In December 2005, widening of the M25 motorway close to Heathrow Airport was completed, together with the new M25 Spur Road which will serve Heathrow Terminal Five. This 12km stretch of motorway is the busiest in Europe, with up to 200,000 vehicles passing through the site every day. The existing dual four lane motorway was widened to dual five lanes between junctions 12 and 14, and dual six lanes between junctions 14 and 15, all within the existing highway boundary.

Notable Features

Gifford, as part of the Gifford WSP Joint Venture, was employed by Balfour Beatty to implement the design of the motorway widening and new Terminal Five Spur Road as part of a Design and Build Contract. All widening needed to be within the original highway boundary, with four lanes remaining open except during limited overnight closures. The total contract period was 137 weeks, with 102 weeks on site for construction. The project was opened three weeks early.

Of particular note was the design adopted for the retaining walls used for widening the existing motorway. Close liaison with the Contractor at detailed design stage led to the development of a modular system using bored concrete piles, an in situ concrete capping beam and precast concrete wall panels. This facilitated rapid construction, and by using an innovative piling method, pile breakdown was eliminated, and so exposure to hand-arm vibration was minimised.

Fehily Timoney Gifford Responsibilities

• Concept design at tender stage
• Design of five new steel composite bridges, including a three-span bridge carrying the Spur Road over the existing motorway, and a landmark structure over the River Colne
• Highways Design, including alignment, drainage, safety fencing, junctions, biological ponds
• Geotechnical Design, including earthworks widening, reinforced earth slopes, soil nailing, stone columns and pile design
• Design of 4.8km of new retaining wall
• Design of 40 new gantries, utilising standard Gifford Gantry System designs
• Design of modifications to over ten other existing structures of significance, including widening to two railway underbridges and pier strengthening to four overbridges
• Detailed design developed to facilitate Contractor’s Traffic Management proposals
• Site design support and examination of the works