Engineers Australia

A risk based assessment of the punch-through potential of jack-up barges

Mark Skinner and Timothy Mote

Abstract

Our Client undertook a series of near-shore ground investigations for a development in the North West Shelf region of Western Australia. The ground investigations were undertaken between 2009 and 2012 using jack-up barges in water of up to 25 m depth. During the 2010 campaign a punch-through incident occurred in which equipment and samples were lost overboard.

A punch-through is the situation whereby one or more legs of the jack-up barge penetrate into the seabed without warning, having previously been supported. This can occur either during the jacking procedure or whilst at working height.

Following the incident, the Client wished to mitigate the risk of further punch-through incidents. We were engaged to develop a method of assessing the risk of punch-through across the site based on geological, geophysical and geotechnical information. The assessment was used to support the 2011 and 2012 near-shore ground investigation campaigns.

Our work involved the back analysis of the punch-though incident, the derivation of a geological model for the site, an assessment of the risk of punch-through over the whole site and the development of an interactive tool which presented location specific assessment results and operational procedures. As new site investigation information was obtained it was imported into the assessment, to improve its accuracy. The results of the assessment were also used by the Client to influence the investigation programme.

This paper presents Arup’s work. The punch-through assessment project is confidential. It is a condition of submission that the Client and the project location cannot be disclosed.