Geotechnical Engineering

 Thome de Gamond, a French engineer, conducted the first systematic geological investigation of the Channel in 1833. He proposed numerous designs for a crossing. Gamond’s work considered the regional geography to design the Channel crossing, and many engineers followed in his footsteps. Although these nineteenth century proposals were ahead of their time, they understood the importance of getting a sound knowledge of the seabed topography and the geology along the route. These factors would be critical to determine the final success of the Channel. Modern geological site investigations use seismic profiling technology. This technology is used for deep-sea exploration, and checks exactly what is under the seabed, but only provides indirect information about the geology. Direct information is obtained through borehole drilling, which collects ground samples.

The geology and topography of the area surrounding the tunnel was studied to determine the most suitable rock layers. Engineers wanted to make sure that no geological hazards could occur along the path of the tunnel. They were able to locate the exact location of the fault zones in the region. The studies revealed that the top and middle layers were not suitable for digging, because of the high porosity, which would allow for water to easily flow. Also, these higher layers of rock contained sand and gravel that would make it hard to drill. Geotechnical engineers found that the best layer was underneath the upper layers. This chalk layer was composed of mostly clay, was able to prevent the water from flowing, and would be the easiest to bore holes through.

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