NETWORK RAIL has demanded that 'unacceptable' levels of leakage into the new Thameslink station box are reduced, it emerged this week.
Water has been pooling in escalator and lift shaft pits, and in 900mm deep cable trenches running beside the tracks through the station. Dispute over the scale of the leakage is understood to have prompted Network Rail to consult its legal advisers.
The station was constructed by Rail Link Engineering (RLE), a joint venture of Bechtel, Arup, Halcrow and Systra responsible for design and project management of High Speed 1. (NCE supplement HS1 - Rail all the way, 14 November 2006).
'There have been dewatering pumps in the station box dealing with water seeping in. There's an unacceptable in ow rate and that needs to be remedied, ' said a project source. 'If the flow is allowed to persist there'll be concerns about the longer-term maintainability of the station.' RLE project manager for the station out Pete Hodkin told NCE that the water was not coming through the station box's contiguous piled walls but that the problem stems from Network Rail's own Thameslink tunnel.
'The adjoining tunnel is brick lined and we believe it acts like a French drain. It's extremely leaky and provides a pathway for water, ' said Hodkin, who also said that some leakage in the box was expected.
'You can either tank a box structure and keep the water out or have an allowable leakage rate and manage any water away through a system of catchment gullies and pipes.
We've gone for the second of those options. But we are well below our maximum allowable leakage limit of 0.25l/h per hour per metre of wall.' Nevertheless RLE has agreed to remedy the situation later this month by excavating a cut-off trench where the brick tunnel meets the station box. A pipeline will connect the trench to an adjacent drainage sump, from which the water will be pumped 'as often as needed', said Hodkin.
'We estimate that there's about 12 hours of work needed to correct the situation, ' he said.
This will be carried out during a 27-hour railway possession on Saturday 27 January.
The Thameslink station box was created by removing a section of Victorian brick tunnel, which runs under the extended St Pancras International station shed. There is a drainage pipeline in the old Thameslink tunnel invert, through which water collected in sumps is meant to drain under gravity. The pipeline was reinstated through the Thameslink station box.
But large volumes of water are not caught by the sumps and pipeline, and drain through the track ballast and into the station box, Hodkin said.