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Preliminary investigations of wave impact on vertical walls with/without parapets and toe protection on deformable beach.

Frandsen, Jannette; Tremblay, Olivier G.; Xhardé, Régis (2016). Preliminary investigations of wave impact on vertical walls with/without parapets and toe protection on deformable beach. In: 6th International Conference on the Application of Physical Modelling in Coastal and Port Engineering and Science (Coastlab16), 10-13 mai 2016, Ottawa, Canada.

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Résumé

Large scale flume measurements of wave impact pressures on a 2.5 m high vertical wall with/without parapets have been undertaken in the context of coastal protection. The wall is mounted at the end of 25.5 m long porous-elastic beach on a slope 1:10. The beach material consists of a sand-gravel mixture. Herein, most tests are carried out with toe protection. Analysis of the data set is in progress and preliminary results are reported in terms of the max. pressure found on the wall structure and jet. Primarily, the inlet conditions consist of regular waves which typically transform into plunging breakers in shallow waters in front of the wall. It has been identified that two types of impacts are critical for the wall design: (1) bore-like wave fronts (flip-through impact) and (2) plunging breakers with airpocket trapped below the crest. The pressures on the structure are highly localized and random and vary rapidly. Similar to impact on circular cylinders, the flip-through impact tends to result in max. wall pressures (herein: 3.4 MPa caused by low aerated impact). The cause of the max. wall pressure and the max vertical jet pressures are not correlated. This is an important point with regards to design of walls both with and without parapets. For most of the cases tested, the wall configuration with parapet works well diverting the wave energy offshore (with jet pressures > 10 MPa) and minimizing structural loads with negligible overtopping. However, occasionally the parapet takes a hit (max. 4.2 MPa) and long waves tend to cause overtopping. With an anticipated full-scale wall height between 5 and 10m, this corresponds to a full-scale pressure on the parapet of 122 MPa using the Bagnold- Mitsuyasu law for a 10 m high wall. Low aeration and flip-through impacts were found to generate critical forces on the coastal structure. Without toe protection, scour develops rapidly. In this case, the parapet configuration does not divert the wave energy effectively and occasionally the wall takes a hit (~3.5 MPa). Irregular inlet waves tend to show similar trends.

Type de document: (Article)
Mots-clés libres: wave breaking; impact pressures; vertical walls; parapets; toe protection; deformable bed; large scale flume
Centre: Centre Eau Terre Environnement
Date de dépôt: 29 nov. 2016 21:52
Dernière modification: 29 nov. 2016 21:52
URI: http://espace.inrs.ca/id/eprint/4849

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