PROPOSALS FOR a second Channel Tunnel are pushing the limits of current tunnel boring technology, the scheme's backers have admitted.
The feasibility study put forward to the French and UK governments by Eurotunnel, operator of the existing link, outlines plans for a 15m excavated diameter, 38km long tunnel.
However, it is unlikely the scheme will go ahead before 2025, 'if at all', said Eurotunnel deputy managing director Alain Bertrand.
Tunnelling projects in Hamburg and Tokyo, where tunnel boring machines have achieved bores of 14.2m and 14.14m diameter respectively, indicate a second tunnel is realistic. But its length would mean pushing new frontiers.
Consultants for the feasibility study Maunsell and French firm Scetauroute are anticipating more advances in TBM technology before work starts.
Road and rail options, calculated to cost ú2.6bn ($4.3bn) and ú3bn respectively, are being considered for the new tunnel.
Unless volumes of freight carried by rail increase dramatically in the next two decades, Eurotunnel's preferred option is the road scheme.
Both schemes will undergo major reappraisal in 2010, when the governments could intervene to appoint an alternative backer for the second tunnel.