EFD Seminar: "Wave-Induced Liquefaction: General approach and case study" 3/21

Wave-Induced Liquefaction: General approach and case study

 by

 Eliezer Kit

 School of Mechanical Engineering, Tel-Aviv University

This talk deals with a study which was aimed to determine the reason of significant change in the pipeline burial depth relative to the undisturbed bottom depth. The gas pipeline was laid in a trench produced by a water jet underneath of the pipeline during the pipe deployment from a specially equipped barge. The water depth along the pipeline trace is about 30 m, and initial trench depth exceeds 3m in the area of interest (along the Mediterranean coast of Israel, off Ashdod).  Comparison between the undisturbed water depths measured in 2004 (when the pipeline was laid) with that in 2006 (after 2 years) indicates that the initial bottom depth remained practically unchanged. The later observation has completely ruled out a possibility that sand erosion at the sea bottom above the pipeline could be responsible for burial depth variation relatively to the bottom depth. A different mechanism, which can explain the significant change in the pipe burial depth, is flotation of the pipeline during the soil liquefaction caused by severe winter storms, especially in the trench backfilled by loose sand.  Soil liquefaction due to storm waves (another source for liquefaction can be an earthquake) is a multidisciplinary topic, which is based on soil mechanics, underground water flow and wave mechanics.  The interaction between the geotechnical experts and their hydrodynamic counterparts is somewhat limited and, thus, a detail discussion of the physics of liquefaction and its consequences on buried pipelines and other marine installations seems to be of high relevance. Then, the results of the case study, which are based on comprehensive field measurements and exposed pipeline observations are presented and discussed. 

Friday, March 21, 2008

ISTB 2, RM 299

1:00 pm