HOCHTIEF successfully delivered the A23 Coulsdon Town Centre Improvement Scheme, building a new 1.7km section of the A23 which by passes the centre of Coulsdon to reduce congestion. Our scope of works involved junction realignment, roundabout construction and several structures, including a road bridge and a 40m jacked box tunnel under the live London to Brighton railway.

Key features:

  • 1.7km road construction
  • Realignment of 2 junctions
  • 2 roundabouts
  • 2-span steel composite road bridge
  • 40m 8,000t reinforced concrete underpass beneath the railway
  • Replacement of footbridge over the railway
  • Environmental mitigation
  • Piled retaining walls
  • Significant utilities

A key element of the scheme was the construction of a 40m, 8,500 tonne concrete jacked box tunnel to take the road under the live railway at Coulsdon Town Station.

At 10m high and 25m wide, the box tunnel was the largest jacked box in Europe at the time. The structure was built offline and then jacked into position while the station and railway remained fully operational.

Our innovative jacking method involved a combined mining and jacking operation, during which over 12,000 tonnes of chalk was excavated. Using up to 14,500 tonnes of hydraulic force, the jacking – divided into three pushes each taking around eight days – averaged 4m per hour. We worked 24-hours a day, 7 days a week for 29 days to complete the works on schedule within the planned 4-week programme.

We continuously monitored the operational railway to ensure its stability and the tunnel was successfully installed without a single minute of train delay. The new road opened on time and budget and the project won the 2006 Ground Engineering Award in London and a Considerate Constructors Silver Award.