The breakthrough of two of the four tunnel boring machines (TBM) currently driving tunnels for the undergrounding of power lines over London's Olympic Park was confirmed by 2012 bosses yesterday.
Two 4.15m diameter TBMs moving in opposite direction underneath Stratford, east London have been boring the tunnels to divert National Grid powerlines, while two 2.82m diameter TBMs have been doing the same for EDF Energy power lines.One of each has now broken through, with the third and final TBM breakthoughs expected after Easter.Contractor on the £80M project is Murphy, with Faber Maunsell as consulting engineer and Arup the Olympic Delivery Authority's (ODA) checking engineer.ODA chief executive David Higgins praised the project's 'tremendous' health and safety record, which has now passed 1M man hours without incident.Murphy managing director James O'Callaghan also praised the record given the challenging nature of London's geology.'The geology has been extremely variable,' said O'Callaghan.'It quickly moves from hard clays to very very soft silts and muds, and we have been working under three bar pressure for most of the drive.'This variability forced the contractor to constantly change the additives it used to condition and stabilise the ground.Currently 52 pylons dominate the landscape in the area making any development difficult. The tunnels will enable the power needed for the Games and the community post-2012 to be carried underground and allow construction work to start next Summer. All tunnelling work is on track to be completed this Summer. Cables and ventilation will then be installed allowing for switchover in Summer 2008.