2. Overview One of the wonders of modern times Longest undersea section of tunnel in the world £12 Billion Cost 35 million passenger vehicles transported so far

3. History First idea 1802 Attempts to survey the seabed in mid 19 th century Work on current tunnel began in mid 1986 Tunnels met December 1990

4. Geological History Ice Age Creation of the English Channel Geology is key to the success of the project

5. Acquiring The Geological Data Boreholes Geophysical Survey Seismic Analysis

6. Detailed Geology The composition Layers of Chalk Permeability Description Average Thickness Typical Intact UCS (Mpa) Middle Chalk85 Lower Chalk Grey Chalk57.5 Upper Chalk Marl208.5 Lower Chalk Marl83.5 Basal Chalk Marl47.5 glaucontic Marl2.513 Zone 6A(Upper)48 Zone 6A(Lower)43.5 Gault Clay(Upper)172 Gault Clay 452 Lower Greensand 50

7. Tunnel Boring Machines (TBMs) French TBMs Earth Pressure Balanced Machines (EPBMs) High water pressure in the Folded and Faulted chalk UK TBMs Double shielded Better tunnelling condition

8. Tunnel Lining 81.9 km of linings Precast Concrete Spherodial Graphite Cast Iron

9. Problems Encountered March 1988: Water inflow on UK’s side 2 miles stretch – 9 months Use of Spheroidal Graphite Cast Iron (SGI) lining Pre-grouting the ground in front