ENGINEERING GEOLOGY OF THE CHANNEL TUNNEL Richard Rae & Robert Hazelhurst March 2006.
-
Upload
lily-burke -
Category
Documents
-
view
217 -
download
4
Transcript of ENGINEERING GEOLOGY OF THE CHANNEL TUNNEL Richard Rae & Robert Hazelhurst March 2006.
ENGINEERING ENGINEERING GEOLOGY OF GEOLOGY OF THE CHANNEL THE CHANNEL
TUNNELTUNNEL
Richard Rae & Robert Hazelhurst March 2006
Contents
• Geology beneath The English Channel
• Selecting the best location for a tunnel
• Successful tunnel construction (1987-1991)
The Weald
• Sediment laid down when area was underwater• Dome arose in Miocene period (~60m years ago)• Dome weathered away over time
Tunnel Location
• Lower chalk layer– soft but stable – easy to excavate, but will stand up even
without supporting walls
– impermeable – comprises 80+% chalk, with some clay mixed in
– depth and thickness of layer acceptable for a tunnel
– layer continuous across whole width of channel
Section through chalk layer beneath English Channel
Route• Tunnel construction began in
1883 – abandoned for military reasons
• 1980’s – advanced oil techniques used
• 4000km of geophysical surveys • 116 marine and 68 land
boreholes • Buried valleys presented major
hazard – route had to stick to rock
Construction
• 8.2 m diameter TBM’s, met in middle • English machines - 'open face' (faster)• French - 'earth pressure balance'
Construction• Tunnels are 51 Km in length, of which 37.5 Km
is undersea• 2400 tonnes/hour spoil = 4 million m3
• 360,000 m² of land reclaimed • TBM placed segmental concrete linings• Gasket or grout to prevent water ingress
• 150 year design life
Problems
• Surveys only provided samples – in between unknown. e.g. aquiclude at crossover
• Water ingress caused TBM breakdowns on English side
• Poor ground conditions on French side• But, generally highly successful - up to 426m
per week – completed ahead of schedule