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DLR Woolwich Arsenal extension hits delays in difficult ground

Tunnelling of the £177M Docklands Light Railway extension under the River Thames to Woolwich Arsenal, east London, has hit delays, NCE has learned.
Contractor Amec started the first of two 2.5km long drives with a bespoke Lovat earth pressure balance tunnel boring machine in May (NCE 11 May).It was meant to arrive in Woolwich last month.But it is understood that the machine has suffered heavy wear to its picks and cutters while passing through a stratum of flint-laden chalk.Amec predicted that abrasion from the flints could pose a problem and designed three locations at which the TBM could be stopped for repairs.It used permeation grouting to stop up water bearing fissures in two areas north and south of the river. The third location was a ventilation shaft on the south bank of the Thames.If the TBM suffered excessive wear, these three refuge points would have enabled Amec to access the cutting head and replace worn picks, without being inundated with water.Even so, the operation would have required the use of compressed air.It was unclear as NCE went to press where the TBM had stopped, or what the impact on schedule was likely to be.The TBM was to have been stripped down and shipped back to the north bank of the Thames, ready to start the second drive in December.

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