Cobham Motorway Service Area, between J9 and J10 of the M25 in Surrey, is the UK’s largest. Its strategic location between Heathrow and Gatwick Airports bridges a 100km gap between M25 service areas. Ramboll was lead engineer for the landmark project from planning to completion and worked closely with client, Highways Agency, Environment Agency, local authorities and contractor. Our services included geotechnical, civil and environmental engineering.
The 20ha development includes a two-storey main building, a hotel, a petrol filling station and associated parking for cars, coaches and heavy goods vehicles. It is built on an environmentally sensitive greenfield site bordered by a river floodplain to the south, a railway line to the east and the M25 to the north.
Computer optimisation of earthworks and levels was crucial for limiting bulk excavation and reducing the carbon footprint of vehicle movements. Ramboll reduced the volume of earthworks from 250,000m3 to 175,000m3, generating significant cost and programme savings.
We developed a surface water drainage strategy in collaboration with the Environment Agency. Two large attenuation ponds with 3500m3 storage accommodate rainfall from extreme storm events and provide public amenity. The SUDS network outfalls at limited flow rate into a nearby watercourse, mitigating flood risks in the locality and downstream.
Foul water from the development is controlled by a 150m3 attenuation tank, complying with Thames Water’s flow rate discharge restrictions on connecting with the public sewer (located approximately 1km north of the service area). Upgrading the existing network, including additional pumping stations, was also required.
Ramboll’s multidisciplinary team met the project’s challenges by forging excellent working relationships with all parties, including those responsible for delivering the new motorway junction. Our robust, innovative and cost-effective design solutions, well-planned construction programme, rigorous project management and site supervision ensured successful and timely project delivery.
Ramboll has produced a hardback book detailing the project — ‘M25 Cobham MSA’.
