SEWER DIVERSION work for the Channel Tunnel Rail Link (CTRL) last week caused a major London railway tunnel to flood, putting it out of action for two days.
A 5km stretch of the Thameslink line between Blackfriars and Kentish Town was shut between the evening of 27 April, and the morning of 30 April.because of the flood.
Water up to 200mm deep in a 550m section of tunnel between King's Cross and St Pancras had to be pumped out and the track disinfected.
'Over eight inches of water collected in the tunnel, well above the level of the rails, blowing all the electrics, ' said a Network Rail spokesman.
Electricity feeding Network Rail pumps, which normally evacuate water collecting in the tunnel was also cut off, worsening the flood's impact.
The flood occurred during work to divert sewers on CTRL contract 105 by joint venture contractor Costain/O'Rourke Civil Engineering/Bachy Soletanche/Emcor Drake & Scull (CORBER).
This was to enable a new underground Thameslink station to be built beneath Midland Road.
CORBER had shut down a section of sewer resting on top of the Thameslink tunnel to allow relocation work to take place.
On 27 April it was pumping sewage around the closed section.
But a sudden heavy rain storm that evening swamped the pumps with stormwater, overwhelming them. This caused the sewer to flood the CTRL Thameslink box work site and Thameslink tunnel itself.
CTRL project manager Rail Link Engineering (RLE) refused to comment on the extent of damage caused to the CTRL works.
It said contractors 'immediately mobilised construction personnel to correct the situation'.
RLE also replaced Network Rail's pumps, which were still not working the day after the incident.
The CTRL project could now face the prospect of compensating train operators for the tunnel closure.