OverviewOne of the wonders of modern timesLongest undersea section of tunnel in the world£12 Billion Cost35 million passenger vehicles transported so far
HistoryFirst idea 1802Attempts to survey the seabed in mid 19th centuryWork on current tunnel began in mid 1986Tunnels met December 1990
Geological HistoryIce AgeCreation of the English ChannelGeology is key to the success of the project
Acquiring The Geological DataBoreholesGeophysical SurveySeismic Analysis
Detailed GeologyThe compositionLayers of ChalkPermeability
DescriptionAverage
ThicknessTypical Intact
UCS (Mpa)Middle Chalk 85
Lower Chalk
Grey Chalk 5 7.5Upper Chalk Marl 20 8.5Lower Chalk Marl 8 3.5Basal Chalk Marl 4 7.5glaucontic Marl 2.5 13Zone 6A(Upper) 4 8Zone 6A(Lower) 4 3.5Gault Clay(Upper) 17 2
Gault Clay 45 2Lower Greensand 50
Tunnel Boring Machines (TBMs)French TBMsEarth Pressure Balanced Machines (EPBMs)High water pressure in the Folded and Faulted chalk
UK TBMsDouble shieldedBetter tunnelling condition
Tunnel Lining81.9 km of liningsPrecast ConcreteSpherodial Graphite Cast Iron
Problems EncounteredMarch 1988:Water inflow on UK’s side2 miles stretch – 9 monthsUse of Spheroidal Graphite Cast Iron (SGI) liningPre-grouting the ground in front
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