It was very disappointing to read of the trials and tribulations experienced by Amec and recalled by Peter South during their boring of the first DLR tunnel beneath the Thames at Woolwich (NCE, 26 April).
The machine selected was stated as being an earth pressure machine (EPB) supplied by Lovats, who have produced many such successful machines over the years.
The strata through which this machine was required to bore appears to have been similar to that encountered during the construction of the recently completed twin CTRL Thames Tunnels. These tunnels were driven using slurry boring machines, which apart from requiring additional centrifuges during the drive, to improve separation rates of the chalk fines, experienced none of the problems reported in this article.
I recall that serious concern had been expressed regarding the risk of driving through the flints contained within the chalk and full protective measures were applied to these machines, but in the event, apart from some wear and tear to the slurry discharge pipes, the machines were not unduly affected.
It would appear that this is another classic case of the tunnelling industry ignoring the lessons learnt from the past and selecting the wrong type of TBM, probably because it was cheaper.
A case of short term gain for long term pain. Will we never learn that paying for the more expensive outlay at the start of a project invariably results in a much less expensive completion price on most major projects?
Neville Harrison, 38, Beacon Hill, Dormansland, Surrey RH7 6RH