Normandy cliff stability: Analysis and repair
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2018 Taylor & Francis Group, London, UK. The cliffs and beaches of Normandy in France were the scene of the D-Day invasion on 6 June 1944 during World War II. One of the landing site was Pointe du Hoc where the German defense was set up on top of 30 m high limestone cliffs. The infrastructure of this defense included canon bunkers back from the front of the cliff and an observation post near the edge of the cliff. In 1944, the Observation Post was 20 m away from the edge but in 2004 that distance was down to 10 m. The reason was the continued erosion process by the sea and associated failures of very large blocks of cliff. The situation became precarious enough that the French administration closed the Observation Post to visitors. In 2006, the American Battle Monument Commission cooperated with the French administration to slow down the erosion process in order to save the historic monuments from falling into the sea. The study conducted by Texas A&M University included field tests with geophysical equipment, coring and sampling of the rock, laboratory testing, and numerical simulations. The study showed that the failure mechanism was the development of deep caverns at the base of the cliffs followed by collapse of the overhang when the depth of the caverns reached a point where the tensile strength of the rock mass was insufficient to carry the rock mass in cantilever. The repair scheme consisted of two parts: backfilling of the caverns and tying the periphery of the foundation of the observation post to deep micropiles. In 2011, the repairs were effected using esthetic concrete to backfill the caverns and deep micropiles around the Observation Post. The Observation Post was reopen to visitors after a ceremony in the presence of D-Day invasion soldiers as well as US and French dignitaries.
