A3 Hindhead Tunnel, Surrey, England

Opportunity

The A3 trunk road connecting Portsmouth with London passed through Hindhead village and the surrounding site of special scientific interest (SSSI), the Devil’s Punch Bowl. Congestion and accidents were major problems and the flow of 30,000 vehicles a day marred the stunning landscape. The challenge was to bypass Hindhead while minimising the environmental impact.

Solution

We designed a 6.7km dual carriageway, including 1.8km located in tunnels underground. Innovations to reduce cost and accelerate the programme included:

• Eliminating a ‘cut-and-cover’ tunnel section and a grade separated junction, as well as fine-tuning the horizontal alignment to shorten the tunnel.
• Using sprayed concrete lining (SCL) in ground conditions where bored tunnelling would normally be used. This saved on the procurement of a tunnel boring machine (TBM) and enabled excavation of a horseshoe-shaped tunnel, cutting the volume of spoil and reducing construction time. Our SCL design also enabled us to reduce the thickness of the tunnel lining.
• Pioneering use of soil nailing and reinforced earth to steepen embankments and cuttings, reducing their width and subsequent land take by an average of 10m.
• Detailed environmental and landscape assessment combined with an open, collaborative relationship with stakeholders to achieve rapid acceptance of our plans, with no statutory objections.
• Ground conditions would have suited excavation by TBM. However, as a road tunnel only needs a horseshoe-shaped cross section with a flat invert rather than the cylindrical tunnel formed by a TBM, we decided to employ sequential excavation for the tunnel. This saved the client around £15M by eliminating the need for a TBM, while cutting the volume of excavated material by 20% and reducing construction time by six months.
• Site preparation was staggered so fauna could migrate to neighbouring woodland and crossing routes for animals such as dormice and badgers were installed.

Outcome

Opened in July 2011, the scheme has been a huge success – reducing congestion and pollution in Hindhead, cutting journey times between the south coast and London – all while enhancing the sensitive environment in the Devil’s Punch Bowl. The scheme increased the amenity value of the area and left a lasting legacy for local communities.

The air is now cleaner, with associated health and wellbeing benefits. The considerable noise impacts of traffic have also been removed, which led the National Trust general manager for the Surrey Hills to comment: “The moment the traffic went underground, you could hear yourself think for the first time in 180 years.”

The integration of a range of measures and design features enhanced the natural landscape. The regeneration of heathland habitat and the introduction of safe cycleways and walking routes has greatly improved the tranquillity of the area and seen the return of rare and diverse breeding birds, such as woodlarks and nightjars.

An environmental monitoring regime has verified the effectiveness of the project’s mitigation measures, which have ensured the long-term wellbeing of the flora and fauna that inhabit this exceptional natural environment.

Extensive landscaping included replanting of local woodland, a green footbridge and vegetated slope finishes. The old A3 was removed and the area restored to heathland, reuniting the Devil's Punch Bowl with Hindhead Common for the first time in almost 200 years.

Finally, the project supports positive economic, social and environmental links between the urban centres of London, Guildford and Portsmouth, and rural communities located in the Surrey Hills and South Downs. Substantial investment was made in the preservation, protection and conservation of natural heritage, and access to the green spaces of the Devil’s Punch Bowl and Hindhead Common has been greatly improved.