Project Brief

When the Olympic Committee announced that the 2012 games would be held in London, plans began to upgrade the surrounding infrastructure to create an awe-inspiring home for 10,000 athletes, 800,000 spectators and 21,000 members of the media.

As part of this work, Network Rail upgraded part of their North London line, appointing Carillion Trenchless Solutions (CTS) to divert the sewer mains on the London Overground Stratford to Richmond line.

The sewers were close to the main line at Caledonian Road Station, located in a deep cutting and in between 50-year-old retaining walls that were strutted with oak beams. These had to remain undisturbed as any damage or movement would result in potential failures of the retaining walls and surrounding infrastructure.

Solution

CTS, together with Network Rail, decided on an installation under the structures using guided auger bore trenchless methods (as open-cut drainage was not suitable). They had originally intended to sink Marshalls Civils & Drainage standard 3000mm and 2000mm caissons, as drive and reception pits. However, this method was revised to cofferdams as the electric and signalling cables alongside required support during the operation.

CTS, as recommended by Network Rail designers, used Marshalls Civils & Drainage caisson manhole units, which were more suitable for high-track loadings compared to standard manholes.

Eight cofferdams were installed along one mile of the track using 450mm and 600mm jacking pipes to not disturb the reinforcements for the retaining walls, which were completed with a live railway track running alongside the construction site.