On 25 Mar, 11:12, Roland Perry wrote:

In message
, at
09:47:14 on Tue, 25 Mar 2008, Lüko Willms
remarked:

Comparing just the length of the cross-London tunnel with the length
of the HS1 London tunnel and wondering why the same length of tunnel
can be much more costly to build

Only a third of the Crossrail budget is building the tunnel.

And that tunnel is under random property and roads in Central London.

HS1 is largely built either in open countryside, or under an existing
railway line.


Quite - the CTRL tunnels rarely venture far away from being underneath
railway alignments that have been in existence for a long time, so
there were far fewer issues about underground utilities (sewers, cable
tunnels etc), building foundations etc and also a greater confidence
that there were not old hidden excavations.

Nevertheless there has been at least one problem caused to the
railways above by the CTRL tunnelling - a retaining wall next to the
North London Line at Dalston Junction had to be rebuilt. See the
bottom of this page for the reference:
http://www.loveplums.co.uk/Tube/Broa...et_line_2.html

In February 2003 there was also one very significant problem caused by
tunnelling away from railway lands in a residential street in central
Stratford where a great hole opened up in the back gardens of houses
on Lavender Street - the CTRL tunnelling seemingly disturbed a network
of old water wells...

http://news.bbc.co.uk/1/hi/england/2741307.stm
http://news.bbc.co.uk/1/hi/england/2742281.stm
http://news.bbc.co.uk/1/hi/england/london/2984955.stm

Tunnelling might be far easier these days but it is certainly not
without its risks - and tunnelling underneath central London carries a
far greater risk.