rr289 - Guidelines for jack-up rigs with particular ...

1 HSE Health & Safety Executive Guidelines for jack-up rigs with particular reference to foundation integrity Prepared by MSL Engineering Limited for the Health and Safety Executive 2004 RESEARCH REPORT 289 HSE Health & Safety Executive Guidelines for jack-up rigs with particular reference to foundation integrity Adrian Dier BSc., MSc., PhD., CEng, MICE, MASCE Brian Carroll BSc., MSc., PhD., CEng, MICE, MASCE Solmaz Abolfathi BSc., MSc. MSL Engineering Limited Platinum Blue House 18 The Avenue Egham Surrey TW20 9AB A jack-up rig is typically used at a dozen or more sites during its service life. It can therefore be expected to encounter a range of water depths, environmental load conditions and soil types. For each candidate site, an assessment is conducted to determine the suitability of the unit for the site and to provide data for the installation operation.

2 Such assessments are normally conducted using the SNAME Technical and Research Bulletin 5-5A. This report addresses the foundations of jack-up rigs, with the overall objective of determining current knowledge and assessment practices. An exhaustive literature search was initially conducted to establish a database of knowledge. A review of the collated data identified case histories of foundation problems, and in turn the major challenges associated with foundation assessment. Various foundation topics ( punch through, bearing and sliding capacity, existing footprints, rack phase difference, etc.) were then examined in depth and recommendations made. In many cases the recommendations are a reaffirmation of existing guidance; in other cases some improvements to the existing guidance are suggested.

3 In the case of rack phase difference, there is no guidance in SNAME and therefore specific provisions have been developed herein. This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy. HSE BOOKS Crown copyright 2004 First published 2004 ISBN 0 7176 2926 0 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the prior written permission of the copyright owner. Applications for reproduction should be made in writing to: Licensing Division, Her Majesty's Stationery Office, St Clements House, 2-16 Colegate, Norwich NR3 1BQ or by e-mail to ii CONTENTS Page No 1 EXECUTIVE 1 2 2 Background and Need for Study.

4 2 Scope of 2 3 AVAILABLE INFORMATION .. 4 Guidance Documents .. 4 Public Domain Literature .. 5 Case 7 4 ASSESSMENT OF INFORMATION .. 15 Initial Penetration and Punch-Through .. 16 Bearing Failure and Settlement .. 20 Sliding Failure .. 29 Previous Footprints .. 32 Significance of Rack Phase Difference (RPD).. 37 47 Layered 52 Foundation Fixity .. 54 jack-up Spudcan/Jacket Pile Interaction .. 57 Effects of Cyclic 59 Debris and Other Objects on 61 Shallow Gas Pockets .. 62 Seafloor Instability .. 63 Liquefaction .. 65 iii 5 KEY FINDINGS AND 70 Key Findings .. 70 Conclusions .. 74 REFERENCES NOTATION iv 1 EXECUTIVE SUMMARY This document summarises a study undertaken by MSL Engineering Limited for the Health and Safety Executive.

5 The study concerns the foundations of jack-up rigs, with the overall objective of determining current knowledge and assessment practices. In addition, some design Guidelines on site specific integrity issues have been prepared. The work began with an exhaustive literature review; over 250 documents were sourced for the study. Case histories were collated from the sourced documents and over 50 incidents relating to jack-up foundation problems were identified. Punch-through (rapid penetration through a stronger soil layer overlying a weaker one) has the highest rate in foundation incident causes, accounting for over 50% of all foundation incidents and the great majority of fatalities that have occurred in jack-up foundation related accidents.

6 The second highest rate in foundation incident causes is for uneven seabed / scour / footprints. The information contained in the literature, including existing guidance within SNAME and ISO documents, was assessed under various headings or topics: punch-through bearing failure and settlement sliding failure footprints rack phase difference (RPD) scour layered soils foundation fixity jack-up spudcan and jacket pile interaction cyclic loading debris shallow gas seafloor instability liquefaction. For each topic and as appropriate: definitions are given, the effects on foundation behaviour are described, analysis/assessment approaches are summarised, mitigation methods are presented, and recommendations are made. In many cases the recommendations are a reaffirmation of existing guidance; in other cases some improvements to the existing guidance are suggested.

7 In the case of rack phase difference, there is no guidance in SNAME or ISO and therefore specific provisions for RPD have been developed. A number of flowcharts have been prepared. The flowcharts serve the following purposes: A visual overview of potential problems that may be encountered during the jack-up installation phase A visual overview of potential problems that may be encountered during in-service operations A summary of the jack-up foundation design process Detailed design process for selected topics. 1 2 INTRODUCTION This report has been prepared by MSL Engineering Limited (MSL) for the Health & Safety Executive (HSE) following various HSE/MSL discussions, and relates to the preparation of Guidelines on the safety and integrity of jack-up rigs, with particular reference to foundation integrity .

8 BACKGROUND AND NEED FOR STUDY Over the past few years, a large number of research and technology development projects have been carried out in the UK and elsewhere on jack-up integrity . One of the primary focuses has been the integrity of jack-up foundation systems and associated risks. Whilst a significant amount of useful information has been generated, there is an increasing recognition that this information is diverse and not easily accessible by the practising engineer. A proposal was therefore prepared for HSE s review and consideration, with the following target objectives: 1. To review/capture all information on the integrity of jack-up rigs, with specific focus on foundation and soil-structure interaction, including case histories.

9 2. To prepare a document on current knowledge and assessment practices. 3. To prepare engineering Guidelines on site specific integrity issues. SCOPE OF WORK The following scope of work was proposed to meet the above stated objectives: i. Capture all documents related to the integrity of jack-up rigs, including standards and recommended practices. ii. Undertake review of the present-day state-of-the-art and state-of-practice. iii. Identify and catalogue all relevant case histories. iv. Undertake a critical appraisal of all the foundation related matters, including the following: Installation of jack-up rigs in close proximity to jacket structures, jack-up spudcan/jacket pile interaction Initial penetration and punch-through Settlement under storm loading/bearing failure Foundation fixity Sliding failure Scour Seafloor instability Shallow gas pockets 2 Existing debris Sloping foundation and eccentric loading, and significance of Rack Phase Difference (RPD) Previous footprints Layered soils Effects of cyclic loading Liquefaction.

10 V. Prepare Guidelines with specific focus on foundation related matters. vi. Prepare report covering all work carried out and all findings. 3 3 AVAILABLE INFORMATION GUIDANCE DOCUMENTS There are two principal sets of guidance documents covering design and assessment engineering of jack-ups, and these are discussed below. In this report, they are generally )referred to as SNAME (1 and ISO (2) for simplicity. SNAME The primary guidance used by the jack-up industry is Society of Naval Architects and Marine Engineers Technical and Research Bulletin 5-5A . The first edition of SNAME was issued in May 1994 and was based on a Joint Industry-Funded Project involving all sections )of the industry. The background to the project was disseminated at a seminar (3 held at City University, London, in September 1993.