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