Offshore Geotechnical Engineering

559 Pages·2011·14.44 MB·English

by  Mark Randolph

Offshore Geotechnical Engineering
Design practice in offshore geotechnical engineering has grown out of onshore prac-
tice, but the two application areas have tended to diverge over the last 30 years, driven
partly by the scale of the foundation and anchoring elements used offshore and partly
by fundamental differences in construction and installation techniques. As a conse-
quence, offshore geotechnical engineering has grown as a speciality.
The book’s structure follows a familiar pattern that mimics the flow of a typical off-
shore project. In the early chapters, it provides a brief overview of the marine environ-
ment, offshore site investigation techniques and interpretation of soil behaviour. It
proceeds to cover geotechnical design of piled foundations, shallow foundations and
anchoring systems. Three topics are then covered that require a more multi-disciplinary
approach: the design of mobile drilling rigs, pipelines and geohazards.
Offshore Geotechnical Engineering serves as a framework for undergraduate and
postgraduate courses, and will appeal to professional engineers specialising in the
offshore industry.
It is assumed that the reader will have some prior knowledge of the basics of soil
mechanics and foundation design. The book includes sufficient basic material to allow
readers to build on this previous knowledge, but focuses on recent developments in
analysis and design techniques in offshore geotechnical engineering.
Mark Randolph is the founding Director of the Centre for Offshore Foundation
Systems at the University of Western Australia, he is a founding Director of the
specialist consultancy, Advanced Geomechanics, and is a former Rankine lecturer.
Susan Gourvenec is a Professor at the Centre for Offshore Foundation Systems at
the University of Western Australia and delivers under-graduate, post-graduate and
industry courses on Offshore Geomechanics.
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Offshore Geotechnical
Engineering
Mark Randolph and Susan Gourvenec
With contributions from
David White and Mark Cassidy
Centre for Offshore Foundation Systems
University of Western Australia
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First published 2011
by Spon Press
2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN
Simultaneously published in the USA and Canada
by Spon Press
270 Madison Avenue, New York, NY 10016, USA
This edition published in the Taylor & Francis e-Library, 2011.
To purchase your own copy of this or any of Taylor & Francis or Routledge’s
collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.
Spon Press is an imprint of the Taylor & Francis Group, an informa business
© 2011 Mark Randolph and Susan Gourvenec
The right of Mark Randolph and Susan Gourvenec to be identified as the
author of this Work has been asserted by him/her in accordance with
sections 77 and 78 of the Copyright, Designs and Patents Act 1988.
All rights reserved. No part of this book may be reprinted or reproduced or
utilised in any form or by any electronic, mechanical, or other means, now
known or hereafter invented, including photocopying and recording, or in
any information storage or retrieval system, without permission in writing
from the publishers.
This publication presents material of a broad scope and applicability. Despite
stringent efforts by all concerned in the publishing process, some typographi-
cal or editorial errors may occur, and readers are encouraged to bring these
to our attention where they represent errors of substance. The publisher and
author disclaim any liability, in whole or in part, arising from information
contained in this publication. The reader is urged to consult with an
appropriate licensed professional prior to taking any action or making any
interpretation that is within the realm of a licensed professional practice.
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
Library of Congress Cataloging in Publication Data
A catalog record has been requested for this book
ISBN 0-203-88909-6 Master e-book ISBN
ISBN13: 978-0-415-47744-4(hbk)
ISBN13: 978-0-203-88909-1(ebk)
Contents
List of figures vi
Preface xxi
Notation xxiv
1 Introduction 1
2 The offshore environment 10
3 Offshore site investigation 29
4 Soil response 113
5 Piled foundations 145
6 Shallow foundations 236
7 Anchoring systems 308
8 Mobile jack-up platforms 361
9 Pipeline and riser geotechnics 404
10 Geohazards 444
Bibliography 484
Index 516
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List of figures
1.1 Superior – The first offshore installation: 1947, Louisiana coast
(from Leffler et al. 2003) 2
1.2 Na Kika development, Gulf of Mexico, 2,000 m water depth
(Newlin 2003a) 2
1.3 Sigsbee escarpment in the Gulf of Mexico (Jeanjean et al. 2005) 3
1.4 Moderate sized steel jacket structure during transport 4
1.5 Schematic of Gullfaks C concrete gravity structure 5
1.6 Jack-up mobile drilling rig 6
1.7 Box anchors for North Rankin Flare Tower (Woodside Petroleum 1988) 7
1.8 Grillage and berm anchors for the Apache Stag field CALM buoy
(redrawn from Erbrich and Neubecker 1999) 8
1.9 Suction anchors assembled on load out vessel 9
2.1 Continental and oceanic crust thickness (in km) 11
2.2 Activity of the earth’s crust (Muller et al. 2008) 12
2.3 Plate and crust tectonics 13
2.4 Topographical features of ocean floors (after Poulos 1988) 13
2.5 Bathymetric shaded relief map showing extent of continental
margins (number key relates to locations in Figure 2.6) 14
2.6 Profiles of ocean floor topography at selected locations 14
2.7 Sediment thickness of the world’s oceans and marginal seas
(Divins 2009) 15
2.8 Sedimentary process of marine deposits (after Silva 1974) 16
2.9 Seabed foraminifera from a deepwater location on the NW
shelf of Australia 17
2.10 Micrographs of (a) calcareous sand and (b) silica sand 18
2.11 Effect of saline pore water on soil strength: salt water (left)
and freshwater (right) (Elton 2001) 20
2.12 Sand ripples 21
2.13 Interaction of current systems (Gerwick 2007) 22
2.14 Circulation of major ocean gyres 23
2.15 Thermohaline circulation – The Global Conveyor Belt 24
2.16 Characteristics of an idealised ocean wave 26
2.17 Orbital paths of water trajectories beneath progressive waves 27
2.18 Superposition of two sinusoidal wave forms
(Dean and Darymple 1991) 27
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List of figures vii
3.1 Conceptual plan for site characterisation 30
3.2 Integration of desk study, geophysics and geotechnics 32
3.3 Main types of geophysical survey: (1) bathymetry mapping by
echo sounder, (2) sea floor mapping by side-scan sonar and
(3) subseabed continuous seismic profiling by means of
an acoustic source and hydrophone receivers (Sullivan 1980) 33
3.4 Schematic of swathe bathymetry system 35
3.5 Side-scan example: images of ship wrecks 35
3.6 Typical towing configuration for sub-bottom profiler
(courtesy: Woodside Energy Ltd) 37
3.7 Hugin 3000 AUV (photo courtesy Kongsberg Marine Ltd,
diagram from Cauquil et al. 2003) 38
3.8 Example of survey line pattern 39
3.9 Continuous seismic profiling – mini air gun record 41
3.10 B athymetry of pockmark from combined side-scan sonar
and multi-beam echo sounder (Cauquil et al. 2003) 41
3.11 3D seismic profiling of pockmark (Cauquil at al. 2003) 42
3.12 Typical scar of an anchor before it buries itself below the seabed 42
3.13 Uneven seabed due to footprints left by jack-up rig 43
3.14 Typical regional hazard features 44
3.15 Downhole and seabed systems 45
3.16 Alternative investigation platforms 46
3.17 Low draft barge for shallow water investigations 47
3.18 Support (or supply) vessel 48
3.19 Dynamically positioned site investigation vessel 48
3.20 Specialised drilling vessel 49
3.21 Jack-up drilling rig 50
3.22 Semi-submersible drilling rig 51
3.23 R emote subsea drilling system (PROD) (a) launching PROD
off stern of vessel and (b) schematic of PROD after deployment
of legs (courtesy of Benthic Geotech) 52
3.24 End views of PROD’s Kerf core barrels (note core catcher on left) 53
3.25 Conventional onshore drilling equipment operating over the
side of a jack-up rig 53
3.26 Seabed frame (SBF) being prepared 54
3.27 Standard 5″ (127 mm) API drill string 55
3.28 Drill bit and schematic of lower part of borehole assembly 56
3.29 Umbilical cable and insertion of tool into drill stem 56
3.30 Offshore classification of rock core 58
3.31 Wheeldrive unit 59
3.32 Schematic of piezocone 60
3.33 Example data record from piezocone penetration test 61
3.34 Soil classification charts (after Robertson 1990) 63
3.35 M odified soil classification chart using excess pore pressure ratio
(Schneider et al. 2008a) 63
3.36 R elationship between cone resistance, relative density and mean
effective stress for silica sands (Jamiolkowski et al. 2003) 64
3.37 Theoretical cone factors 66
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viii List of figures
3.38 Theoretical dissipation curves for piezocone 67
3.39 T-bar penetrometer (a) wheeldrive and (b) downhole 68
3.40 Piezoball penetrometer (Kelleher and Randolph 2005) 68
3.41 R esistance factors for T-bar in rate dependent softening soil
(Zhou and Randolph 2009a) 70
3.42 C omparison of net penetration and extraction resistances for cone,
T-bar, small T-bar (L/d = 4), ball and plate (Chung and Randolph 2004) 71
3.43 E xample cyclic T-bar and ball penetrometer tests (a) cyclic ball
penetrometer test and (b) resistance degradation curves 72
3.44 Box-core being landed and (right) set up for miniature T-bar
penetrometer tests 76
3.45 T he STACOR gravity piston sampler. Reprinted from Borel, D.,
Puech, A., Dendani, H. and de Ruijter, M. (2002) ‘High quality
sampling for deep-water geotechnical engineering: the STACOR®
Experience’. Ultra Deep Engineering and Technology, Brest, France,
by kind permission of PennWell Conferences and Exhibitions 77
3.46 Removing the sampling tube from the piston corer 78
3.47 Typical borehole log 80
3.48 Photograph of cores, showing depth ranges 81
3.49 Schematic of X-ray test 82
3.50 E xample radiographs (a) internal sample disturbance and
(b) sand over clay sediment interface 83
3.51 Typical result from XRD analysis 84
3.52 Split soil sample revealing fossils and previous life forms 85
3.53 E SEM images of calcium carbonate sediments from the NW
Shelf of Australia (a) aragonite crystals, (b) sand from near
the Goodwyn gas field and (c) muddy carbonate silt from
near the Gorgon gas field 85
3.54 M icrophotos from thin sections of cemented calcium carbonate
sediments from the NW Shelf of Australia (a) thin section of
calcarenite, (b) cement build up around the fringes of two
particles and (c) cement fringes around solid particles (black)
and voids (grey) 86
3.55 E ffect of soil fabric on stress strain response of carbonate silt
(a) material reconstituted with water, (b) material reconstituted
with synthetic flocculent, (c) natural material and (d) simple shear
stress–strain responses 87
3.56 E xample particle size distribution data (four calcareous and one silica
soil samples from offshore and onshore Western Australia) 88
3.57 Plasticity chart for classification of soils 91
3.58 Standard oedometer apparatus 93
3.59 Rowe cell oedometer 93
3.60 Oedometer data from carbonate silt 94
3.61 Deduction of consolidation coefficient from root time
compression response 94
3.62 Direct shear apparatus 95
3.63 Triaxial test apparatus and sample with local strain measuring devices 97
3.64 Schematic of triaxial test apparatus and stress conditions 98
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List of figures ix
3.65 Typical presentation of results from triaxial test 100
3.66 Simple shear apparatus 101
3.67 Schematic of simple shear test apparatus and stress conditions 101
3.68 Alternative interpretation of simple shear test 102
3.69 Typical presentation of results from simple shear test 103
3.70 Stress conditions under a gravity base structure 105
3.71 Shear modes along an axially loaded pile 106
3.72 Rod shear apparatus 108
3.73 Calibration chamber test for grouted piles 108
3.74 Model jack-up rig for laboratory floor testing (Vlahos 2004) 109
3.75 Schematic of centrifuge with experiment on the swinging platform 110
3.76 Principle of 1:1 scaling of stress between prototype and
centrifuge model 110
3.77 Example centrifuge models: (a) suction caisson (upper) and
(b) drag anchor (lower) 111
3.78 Example centrifuge modelling of jack-up rig (Bienen et al. 2009) 112
4.1 Stress changes in an elastic half space due to a vertical point
load at the surface (Boussinesq 1885) 114
4.2 Elastic deformations (a) undeformed (b) Young’s modulus
describing change in length and Poisson’s ratio describing
change in width (c) shear modulus describing change in shape
at constant volume (d) bulk modulus describing change in volume
at constant shape (Muir Wood 1990) 115
4.3 Mandel-Cryer effect; excess pore pressure response with depth
beneath a strip load (Schiffman et al. 1969) 118
4.4 Effect of Poisson’s ratio on three-dimensional consolidation response
beneath a rigid circular raft of radius, a (Chiarella and Booker 1975,
permeable raft and Booker and Small 1986, impermeable raft) 119
4.5 Effect of strain rate on constant rate of strain oedometer test
(Leroueil et al. 1985) 120
4.6 Comparison of compressibility of silica and calcareous sands 120
4.7 Dilation and contraction during shearing (Bolton 1991) 121
4.8 Saw tooth model of dilation (Bolton 1991) 122
4.9 Idealisation of dilation and contraction in a direct shear test 123
4.10 C omparison of drained triaxial tests on (a) silica sand and
(b) calcareous sand (Golightly and Hyde 1988) 124
4.11 The critical state concept 125
4.12 Dilatancy dependency on density and stress level 126
4.13 Stress and state paths during drained and undrained shearing 126
4.14 S tress and state paths during an isotropically consolidated
undrained triaxial compression test (a) wet of critical and
(b) dry of critical 127
4.15 Stress and state paths followed during construction of a
gravity-based foundation 128
4.16 Stress and state paths followed during staged loading 130
4.17 A mplitude and frequency of cyclic loading of (a) a typical storm
sequence and (b) a laboratory cyclic loading test 131
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