Observations of momentary liquefaction caused by breaking waves around a coastal structure

Mathieu Mory (1) , Hervé Michallet (2) , Stéphane Abadie , I. Piedra-Cueva (1) , D. Bonjean (3) , P. Breul (4) , M. Cassen

1 ENSGTI - Ecole Nationale supérieure en génie des Technologie Industrielle
2 LEGI - Laboratoire des Écoulements Géophysiques et Industriels [Grenoble]
3 3S - Laboratoire Sols, Solides, Structures
4 LERMES-CUST

This paper aims at demonstrating the occurrence of momentary liquefaction in a sandy soil around a coastal structure subject to wave forcing. This was made in the field, using as coastal structure a bunker from the Second World War that is currently situated on the beach at Capbreton on the Atlantic coast of south-west France. By positioning pressure sensors at different levels inside the soil, time series of simultaneous pore pressure measurements were acquired while the position of the soil level was monitored. Analysis of the pressure measurements demonstrated that the sediment layer on top of the bed does not remain continuously in static equilibrium. An upward pressure gradient was sometimes observed, which could overcome the effective weight of the sediment. Pore pressure variations inside the soil were compared, using a Fourier analysis of the time series, with the theory put forward by Sakai et al. (1992) whereby the damping of pore pressure variations inside the soil can be quantified. A surprisingly good agreement is found when the gas content is adjusted in the model to 1%. This indicates the existence of a significant amount of gas inside the soil. This property is confirmed in the field by geo-endoscopic videos.

Domaines: Mécanique des fluides [physics.class-ph]; Mécanique des fluides [physics.class-ph]

Mathieu Mory, Hervé Michallet, Stéphane Abadie, I. Piedra-Cueva, D. Bonjean, et al.. Observations of momentary liquefaction caused by breaking waves around a coastal structure. 29th Conference on Coastal Engineering, Sep 2004, Lisbon, Portugal. ⟨10.1142/9789812701916_0339⟩. ⟨hal-00260392⟩