Background

As part of the North London Line upgrade works in preparation for the London 2012 Olympic Games, infrastructure improvements were required along the London Overground route between Stratford and Richmond. This included the diversion of existing sewer mains beneath live railway infrastructure.

The section of works at Caledonian Road Station presented particularly complex constraints due to the age and condition of the surrounding structures and the operational demands of the railway.

The challenge

The main railway line at Caledonian Road Station is located within a deep cutting, bounded by retaining walls more than 50 years old.

 These walls are strutted using oak beams that were required to remain completely undisturbed, as any movement or damage could compromise the integrity of the retaining structures and surrounding railway infrastructure.

Additional challenges included:

  • Live railway operations continuing throughout the works
  • High track loadings acting on underground structures
  • Electric and signalling cables running alongside the excavation area
  • Open cut drainage being deemed unsuitable due to structural and operational risk

A controlled, low impact construction technique was essential.

The solution

Working in collaboration with Network Rail, Carillion Trenchless Solutions adopted a guided auger bore trenchless installation method, allowing sewer diversions to be installed beneath the existing structures without disturbing the retaining walls or track infrastructure.

Marshalls supplied precast concrete caisson manhole units, selected on the recommendation of Network Rail designers. These units were specified due to their ability to accommodate very high railway track loadings, exceeding the performance of standard manhole solutions.

The original proposal to use standard 3000mm and 2000mm caissons as drive and reception pits was revised. Instead, cofferdams were installed to support adjacent electrical and signalling cables during the works.

In total:

  • Eight cofferdams were installed along approximately one mile of track
  • 450mm and 600mm jacking pipes were used
  • All works were completed with live railway tracks operating alongside the construction activity

The outcome

The use of Marshalls precast caisson units enabled the successful diversion of sewer mains within a highly constrained railway environment.

  • Trenchless installation avoided disturbance to historic retaining walls
  • High strength caisson units safely accommodated rail loadings
  • Live railway services were maintained throughout construction
  • Structural risks to surrounding infrastructure were minimised

The project demonstrates how robust precast access solutions can support trenchless drainage works on heavily constrained and operational rail assets.