Applied Ocean Research 31 (2009) 25–30 Contents lists available at ScienceDirect Applied Ocean Research journal homepage: www.elsevier.com/locate/apor The effect of structures on the wave-induced liquefaction potential of seabed sand deposits R. Noorzad a,∗ , S. Safari b , M. Omidvar c a Civil Engineering Department, Nooshirvani University of Technology, P. O. Box 484, Babol, Iran b Consultant Engineers, Tehran, Iran c Engineering Faculty, University of Golestan, Gorgan, Iran article info Article history: Received 22 October 2007 Received in revised form 14 December 2008 Accepted 30 March 2009 Available online 4 June 2009 Keywords: Liquefaction Sea wave Marine structure Sand deposit abstract One of the important design considerations for marine structures situated on sand deposits is the potential for instability caused by the development of excess pore pressure as a result of wave loading. A build- up of excess pore pressure may lead to initial liquefaction. The current practice of liquefaction analysis in marine deposits neglects the effects of structures over seabed deposits. However, analyses both in terrestrial and marine deposits have shown that the presence of a structure, depending on the nature of the structure and initial soil conditions, may decrease or increase the liquefaction potential of underlying deposits. In the present study, a wave-induced liquefaction analysis is carried out using mechanisms similar to earthquake-induced liquefaction. The liquefaction potential is first evaluated using wave- induced liquefaction analysis methods for a free field. Then by applying a structure force on the underlying sand deposits, the effect of the structure on the liquefaction potential is evaluated. Results showed that depending on the initial density of the sand deposits and different structures, water depths and wave characteristics, the presence of a structure may increase or decrease the liquefaction potential of the underlying sand deposits. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction In the past three decades, wave-induced liquefaction of seabed sand deposits has been a serious challenge for the development of near-shore and offshore structures. Seabed soil response to progressive water waves has an essential role in the analysis and design of marine structures. An important part of this response observed in non-cohesive deposits is the instability potential of the seabed as a result of excess pore pressure build-up in the soil due to cyclic wave action. Near the shore – away from the surf zone – where waves are still stable and the water is not very deep, the seabed is affected by considerable dynamic pressure due to the action of transient waves. This pressure produces cyclic stress in the soil and may result in a gradual build-up of pore pressure. The pore pressure may build up to an amount equal to the initial vertical effective stress, causing initial liquefaction. Structures built on such deposits are prone to instability depending on the position and progression of the excess pore pressure. An example of such instability is the failure of 3.05 m diameter steel pipes in Lake Ontario during a storm event [1,2]. The reason for the failure of ∗ Corresponding author. Tel.: +98 111 3231707. E-mail addresses: rnoorzad@nit.ac.ir, reza_noorzad@yahoo.com (R. Noorzad). the pipes was reported to be liquefaction of the temporary backfill. Another example is the failure of a breakwater being built at the western port of Nigatta, Japan, in October 1976. One of the causes of the instability was believed to be a rapid build-up of residual pore pressure in sand deposits and a resulting sliding circular failure [3]. Soil liquefaction due to progressive wave action has also been observed in experimental studies [4]. Sassa and Sekiguchi studied the wave-induced liquefaction of fine-grained sand seabeds in the centrifuge and pointed out the progressive nature of these deposits [5]. The mechanism of wave-induced liquefaction may be classified into two groups depending on the process of pore pressure generation [6,7]. The first group occurs similarly to earthquake-induced liquefaction due to cyclic shear stress which causes a gradual build-up of pore pressure in the seabed. The second group has a transient nature and occurs repeatedly during storm events. The first mechanism occurs when shear stress is dominant and is followed by considerable deformations in the seabed, while the latter occurs in cases where the loading is primarily due to vertical wave action and relatively small seabed deformations occur. Liquefaction of sand deposits by both mentioned mechanisms results in damage to marine structures. The current practice in analysis of the liquefaction potential of deposits underlying marine structures neglects the presence of the structure itself. But theoretical studies and experimental observations by researchers such as Rollins and Seed [8] and 0141-1187/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apor.2009.03.002