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Lower Lea Valley Cable Tunnels – A Case Study of a Program Critical Project


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Author S Woodrow


The purpose of the Lower Lea Valley Cable Tunnel project is to relocate the
overhead power lines circuits, which currently cross the proposed site for the
2012 London Olympics in East London. This was the first contract to be awarded
as an Olympic project and is on the critical path for the proposed Olympic Park
as the construction of the Olympic village, stadium and other venues cannot
begin until the tunnels are complete, the cables installed and the overhead
power lines removed. The tunnelling works for the scheme include two parallel
tunnels between Hackney and West Ham. Each tunnel is approximately 6 km in
length. One tunnel is 4.15 m ID and connects the National Grid substations. The
other is 2.82 m ID and connects the EDF Energy substations. The tunnels were
constructed through mixed ground using four earth pressure balance tunnel boring
machines. These were driven simultaneously from two drive shafts within a single
site. The 12 km of main tunnels were constructed within a year from start to
finish, with completion in June 2007.

The shafts range between 6 m and 15 m ID. These were constructed using
a combination of caisson sinking and underpinning techniques. Dewatering was
adopted to suit the groundwater conditions.
Other works
include the design and construction of the head house buildings, cable and
ventilation culverts, mechanical and electrical (M&E) installations and all
associated works.

In addition to the above, a further 1 km of tunnel and two shafts were added
to the project scope connecting the EDF Energy tunnel to the substation at Bow.
These additional works provided further challenges to the project to ensure that
these works were constructed within the program constraints for the 2012 London
Olympics. This involved refurbishing one of the tunnel boring machines from the
main EDF Energy tunnel drives and relaunching the machine to construct the Bow
tunnel. The Bow tunnel was constructed within two and a half months, with the
tunnel boring machine breaking through in August, ahead of schedule.

The main challenge presented by this project is the program constraints. This
project outlines the requirement for team work between the client, stakeholders,
contractor and designer in order to provide program certainty. A close working
relationship between the contractor and the designer is required to provide
value engineered, time-saving solutions to mitigate the risks associated with
the design and construction program.