Table Of ContentICE manual of
geotechnical engineering
Volume 2
Geotechnical Design,
Construction and Verification
Edited by
John Burland
Imperial College London, UK
Tim Chapman
Arup Geotechnics, UK
Hilary Skinner
Donaldson Associates Ltd, UK
Michael Brown
University of Dundee, UK
ice | manuals
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Published by ICE Publishing, 40 Marsh Wall, London E14 9TP, UK
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First published 2012
Future titles in the ICE Manuals series from ICE Publishing
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Currently available in the ICE Manual series from ICE Publishing
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A catalogue record for this book is available from the British Library
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© Institution of Civil Engineers 2012
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While every effort has been made to ensure that the statements made and the opinions expressed
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ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers
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Preface
We began to formulate the initial ideas for this Manual as early as 2006. It had become apparent to us that
civil and structural engineers not specialising in geotechnics face a daunting knowledge gap when they
come up against a geotechnical problem. Most civil engineers leave university with very little grounding
in geotechnical engineering. They will have a fair grasp of applied mechanics (mainly aimed at structural
engineering). They will have had a basic introduction to geology and they will have studied the elements of
soil mechanics and rock mechanics. But a recent graduate usually lacks a coherent understanding of the
approach to, and methods of, geotechnical engineering and how these differ from other more widely prac-
tised branches of engineering. A survey carried out by ICE Publishing showed that information tends to be
obtained from a wide range of sources through word of mouth, the internet and various publications. For
the young practitioner this leads to a fragmented approach. Much of the geotechnical material is written by
specialists for specialists and its ad hoc application by a general practitioner is often inappropriate and can
be extremely dangerous. We felt that it would be of great benefi t to our profession to provide a single fi rst-
port-of-call authoritative reference source aimed at informing the less experienced engineer. To our delight
this concept was endorsed by the ICE Best Practice Panel and the British Geotechnical Association and has
offered a unique opportunity to provide authoritative guidance within a coherent framework of good geotech-
nical engineering.
This ICE Manual of Geotechnical Engineering has been a labour of love! The contribution of 99 contributors
and 10 section editors has made it possible to distil a great deal of experience from the profession into the
books you see here. Don’t imagine this will cover everything that a geotechnical engineer will face in their
career – but it provides a “starting point” from which to build experience whilst remaining grounded in robust
fundamentals.
As mentioned previously, the Manual is aimed at people in the early stage of their careers who need a readily
accessible source of information when working in new aspects of geotechnical engineering. However it is
expected that it also should prove valuable to all geotechnical engineering professionals. The aim has been
to produce a manual that addresses the practice of geotechnical engineering in the 21st century including
contemporary procurement, process and design standards and procedures. The grouping of chapters has
been carefully chosen to facilitate a multi-disciplinary and holistic approach to the solution of construction
challenges. A key message is the importance of drawing on “well-winnowed experience” for the smooth and
reliable execution of projects. Such experience is best gained by working closely with a suitably experienced
design or construction team.
It is hoped that this Manual will help in the training and development of the next generation of geotechnical
engineers and will act as a useful source of reference to those with more experience.
The Editors are grateful to all those contributors and section editors who have generously given so much of
their time and knowledge in producing such a comprehensive book.
John Burland, Tim Chapman, Hilary Skinner and Michael Brown
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ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers
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Contents
Volume II
Foreword and endorsement
xi
Preface
xiii
List of contributors
xv
SECTION 5: Design of foundations
729
Section Editor: A. S. O’Brien
Chapter 51: Introduction to Section 5
731
A. S. O’Brien
Chapter 52: Foundation types and conceptual
design principles
733
A. S. O’Brien
52.1 Introduction
733
52.2 Foundation types
734
52.3 Foundation selection – conceptual design principles
735
52.4 Allowable foundation movement
747
52.5 Design bearing pressures
752
52.6 Parameter selection – introductory comments
754
52.7 Foundation selection – a brief case history
759
52.8 Overall conclusions
763
52.9 References
763
Chapter 53: Shallow foundations
765
A. S. O’Brien and I. Farooq
53.1 Introduction
765
53.2 Causes of foundation movements
765
53.3 Construction processes and design considerations
768
53.4 Applied bearing pressures, foundation layout and
interaction effects
773
53.5 Bearing capacity
774
53.6 Settlement
778
53.7 Information requirements and parameter selection
789
53.8 Case history for a prestigious building on glacial tills
796
53.9 Overall conclusions
799
53.10 References
800
Chapter 54: Single piles
803
A. Bell and C. Robinson
54.1 Introduction
803
54.2 Selection of pile type
803
54.3 Axial load capacity (ultimate limit state)
804
54.4 Factors of safety
814
54.5 Pile settlement
814
54.6 Pile behaviour under lateral load
816
54.7 Pile load testing strategy
818
54.8 Defi nition of pile failure
820
54.9 References
820
Chapter 55: Pile-group design
823
A. S. O’Brien
55.1 Introduction
823
55.2 Pile-group capacity
824
55.3 Pile-to-pile interaction: vertical loading
827
55.4 Pile-to-pile interaction: horizontal loading
834
55.5 Simplifi ed methods of analysis
834
55.6 Differential settlement
841
55.7 Time-dependent settlement
841
55.8 Optimising pile-group confi gurations
841
55.9 Information requirements for design and parameter selection
843
55.10 Ductility, redundancy and factors of safety
846
55.11 Pile-group design responsibility
847
55.12 Case history
847
55.13 Overall conclusions
850
55.14 References
850
Chapter 56: Rafts and piled rafts
853
A. S. O’Brien, J. B. Burland and T. Chapman
56.1 Introduction
853
56.2 Analysis of raft behaviour
854
56.3 Structural design of rafts
860
56.4 Design of a real raft
861
56.5 Piled rafts, conceptual design principles
863
56.6 Raft-enhanced pile groups
868
56.7 Pile-enhanced rafts
879
56.8 A case history of a pile-enhanced raft – the Queen Elizabeth II
Conference Centre
883
56.9 Key points
884
56.10 References
885
Chapter 57: Global ground movements and their effects
on piles
887
E. Ellis and A. S. O’Brien
57.1 Introduction
887
57.2 Negative skin friction
888
57.3 Heave-induced tension
891
57.4 Piles subject to lateral ground movements
893
57.5 Conclusions
897
57.6 References
897
Chapter 58: Building on fi lls
899
H. D. Skinner
58.1 Introduction
899
58.2 Engineering characteristics of fi ll deposits
899
58.3 Investigation of fi lls
900
58.4 Fill properties
902
58.5 Volume changes in fi lls
904
58.6 Design issues
907
58.7 Construction on engineered fi lls
909
58.8 Summary
910
58.9 References
910
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ice | manuals
Chapter 59: Design principles for ground improvement
911
R. Essler
59.1 Introduction
911
59.2 General design principles for ground improvement
912
59.3 Design principles for void fi lling
913
59.4 Design principles for compaction grouting
914
59.5 Design principles for permeation grouting
916
59.6 Design principles for jet grouting
924
59.7 Design principles for vibrocompaction and vibroreplacement
929
59.8 Design principles for dynamic compaction
933
59.9 Design principle for deep soil mixing
934
59.10 References
937
Chapter 60: Foundations subjected to cyclic and
dynamic loads
939
M. Srbulov and A. S. O’Brien
60.1 Introduction
939
60.2 Cyclic loading
939
60.3 Earthquake effects
940
60.4 Offshore foundation design
948
60.5 Machine foundations
950
60.6 References
951
SECTION 6: Design of retaining structures
955
Section Editor: A. Gaba
Chapter 61: Introduction to Section 6
957
A. Gaba
Chapter 62: Types of retaining walls
959
S. Anderson
62.1 Introduction
959
62.2 Gravity walls
959
62.3 Embedded walls
961
62.4 Hybrid walls
966
62.5 Comparison of walls
966
62.6 References
968
Chapter 63: Principles of retaining wall design
969
M. Devriendt
63.1 Introduction
969
63.2 Design concepts
969
63.3 Selection of design parameters
973
63.4 Ground movements and their prediction
977
63.5 Principles of building damage assessment
979
63.6 References
980
Chapter 64: Geotechnical design of retaining walls
981
A. Pickles
64.1 Introduction
981
64.2 Gravity walls
981
64.3 Reinforced soil walls
988
64.4 Embedded walls
988
64.5 References
999
Chapter 65: Geotechnical design of retaining wall
support systems
1001
S. Anderson
65.1 Introduction
1001
65.2 Design requirements and performance criteria
1001
65.3 Types of wall support systems
1002
65.4 Props
1003
65.5 Tied systems
1005
65.6 Soil berms
1006
65.7 Other systems of wall support
1008
65.8 References
1009
Chapter 66: Geotechnical design of ground anchors
1011
M. Turner
66.1 Introduction
1011
66.2 Review of design responsibilities
1014
66.3 The design of ground anchors for the support of
retaining walls
1015
66.4 Detailed design of ground anchors
1017
66.5 References
1029
Chapter 67: Retaining walls as part of complete
underground structure
1031
P. Ingram
67.1 Introduction
1031
67.2 Interfaces with structural design and other disciplines
1031
67.3 Resistance to lateral actions
1033
67.4 Resistance to vertical actions
1034
67.5 Design of bored piles and barrettes to support/resist vertical
loading beneath base slab
1036
67.6 References
1037
SECTION 7: Design of earthworks, slopes and
pavements
1039
Section Editor: Paul A. Nowak
Chapter 68: Introduction to Section 7
1041
P. A. Nowak
Chapter 69: Earthworks design principles
1043
P. A. Nowak
69.1 Historical perspective
1043
69.2 Fundamental requirements of earthworks
1043
69.3 Development of analysis methods
1044
69.4 Factors of safety and limit states
1044
69.5 References
1046
Chapter 70: Design of new earthworks
1047
P. A. Nowak
70.1 Failure modes
1047
70.2 Typical design parameters
1050
70.3 Pore pressures and groundwater
1053
70.4 Loadings
1055
70.5 Vegetation
1057
70.6 Embankment construction
1058
70.7 Embankment settlement and foundation treatment
1059
70.8 Instrumentation
1062
70.9 References
1063
Chapter 71: Earthworks asset management
and remedial design
1067
B. T. McGinnity and N. Saffari
71.1 Introduction
1067
71.2 Stability and performance
1069
71.3 Earthwork condition appraisal, risk mitigation and control
1073
71.4 Maintenance and remedial works
1075
71.5 References
1085
Chapter 72: Slope stabilisation methods
1087
P. A. Nowak
72.1 Introduction
1087
72.2 Embedded solutions
1087
72.3 Gravity solutions
1088
72.4 Reinforced/nailed solutions
1089
72.5 Slope drainage
1090
72.6 References
1091
Chapter 73: Design of soil reinforced slopes
and structures
1093
S. Manceau, C. Macdiarmid and G. Horgan
73.1 Introduction and scope
1093
73.2 Reinforcement types and properties
1093
73.3 General principles of reinforcement action
1094
73.4 General principles of design
1096
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Chapter 80: Groundwater control
1173
M. Preene
80.1 Introduction
1173
80.2 Objectives of groundwater control
1173
80.3 Methods of groundwater control
1175
80.4 Groundwater control by exclusion
1175
80.5 Groundwater control by pumping
1176
80.6 Design issues
1185
80.7 Regulatory issues
1188
80.8 References
1189
Chapter 81: Types of bearing piles
1191
S. Wade, R. Handley and J. Martin
81.1 Introduction
1191
81.2 Bored piles
1192
81.3 Driven piles
1206
81.4 Micro-piles
1217
81.5 References
1222
Chapter 82: Piling problems
1225
V. Troughton and J. Hislam
82.1 Introduction
1225
82.2 Bored piles
1226
82.3 Driven piles
1230
82.4 Identifying and resolving problems
1233
82.5 References
1235
Chapter 83: Underpinning
1237
T. Jolley
83.1 Introduction
1237
83.2 Types of underpinning
1237
83.3 Factors infl uencing the choice of underpinning type
1240
83.4 Bearing capacity of underpinning and adjacent footings
1241
83.5 Shoring
1242
83.6 Underpinning in sands and gravel
1243
83.7 Dealing with groundwater
1243
83.8 Underpinning in relation to subsidence settlement
1245
83.9 Safety aspects of underpinning
1245
83.10 Financial aspects
1246
83.11 Conclusion
1246
83.12 References
1246
Chapter 84: Ground improvement
1247
C. J. Serridge and B. Slocombe
84.1 Introduction
1247
84.2 Vibro techniques (vibrocompaction and vibro stone columns)
1247
84.3 Vibro concrete columns
1259
84.4 Dynamic compaction
1261
84.5 References
1268
Chapter 85: Embedded walls
1271
R. Fernie, D. Puller and A. Courts
85.1 Introduction
1271
85.2 Diaphragm walls
1271
85.3 Secant pile walls
1276
85.4 Contiguous pile walls
1280
85.5 Sheet pile walls
1280
85.6 Combi steel walls
1284
85.7 Soldier pile walls (king post or Berlin walling)
1285
85.8 Other wall types
1287
85.9 References
1288
Chapter 86: Soil reinforcement construction
1289
C. Jenner
86.1 Introduction
1289
86.2 Pre-construction
1289
86.3 Construction
1290
86.4 Post-construction
1294
86.5 References
1294
73.5 Reinforced soil walls and abutments
1097
73.6 Reinforced soil slopes
1102
73.7 Basal reinforcement
1104
73.8 References
1106
Chapter 74: Design of soil nails
1109
M. J. Whitbread
74.1 Introduction
1109
74.2 History and development of soil nailing techniques
1109
74.3 Suitability of ground conditions for soil nailing
1109
74.4 Types of soil nails
1110
74.5 Behaviour of soil nails
1110
74.6 Design
1110
74.7 Construction
1112
74.8 Drainage
1113
74.9 Corrosion of soil nails
1113
74.10 Testing soil nails
1113
74.11 Maintenance of soil nailed structures
1113
74.12 References
1113
Chapter 75: Earthworks material specifi cation,
compaction and control
1115
P. G. Dumelow
75.1 The earthworks specifi cation
1115
75.2 Compaction
1124
75.3 Compaction plant
1128
75.4 Control of earthworks
1130
75.5 Compliance testing of earthworks
1132
75.6 Managing and controlling specifi c materials
1135
75.7 References
1141
Chapter 76: Issues for pavement design
1143
P. Coney, P. Gilbert and Reviewed by P. Fleming
76.1 Introduction
1143
76.2 Purpose of pavement foundation
1144
76.3 Pavement foundation theory
1145
76.4 Brief recent history of pavement foundation design
1145
76.5 Current design standards
1146
76.6 Sub-grade assessment
1150
76.7 Other design issues
1152
76.8 Construction specifi cation
1153
76.9 Conclusion
1154
76.10 References
1154
SECTION 8: Construction processes
1157
Section Editor: T. P. Suckling
Chapter 77: Introduction to Section 8
1159
T. P. Suckling
Chapter 78: Procurement and specifi cation
1161
T. P. Suckling
78.1 Introduction
1161
78.2 Procurement
1161
78.3 Specifi cations
1163
78.4 Technical issues
1164
78.5 References
1165
Chapter 79: Sequencing of geotechnical works
1167
M. Pennington and T. P. Suckling
79.1 Introduction
1167
79.2 Design construction sequence
1167
79.3 Site logistics
1168
79.4 Safe construction
1168
79.5 Achieving the technical requirements
1170
79.6 Monitoring
1172
79.7 Managing changes
1172
79.8 Common problems
1172
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Chapter 94: Principles of geotechnical monitoring
1363
J. Dunnicliff, W. A. Marr and J. Standing
94.1 Introduction
1363
94.2 Benefi ts of geotechnical monitoring
1363
94.3 Systematic approach to planning monitoring programmes using
geotechnical instrumentation
1366
94.4 Example of a systematic approach to planning a monitoring
programme: using geotechnical instrumentation for an
embankment on soft ground
1370
94.5 General guidelines on execution of monitoring programmes
1372
94.6 Summary
1376
94.7 References
1376
Chapter 95: Types of geotechnical instrumentation and
their usage
1379
J. Dunnicliff
95.1 Introduction
1379
95.2 Instruments for monitoring groundwater pressure
1379
95.3 Instruments for monitoring deformation
1384
95.4 Instruments for monitoring load and strain in structural members
1389
95.5 Instruments for monitoring total stress
1392
95.6 General role of instrumentation, and summaries of instruments
to be considered for helping to provide answers to various
geotechnical questions
1393
95.7 Acknowledgement
1400
95.8 References
1402
Chapter 96: Technical supervision of site works
1405
S. Glover and J. Chew
96.1 Introduction
1405
96.2 Reasons for supervision of geotechnical works
1406
96.3 Preparing for a site role
1408
96.4 Managing the site works
1410
96.5 Health and safety responsibilities
1414
96.6 Supervision of site investigation works
1414
96.7 Supervision of piling works
1416
96.8 Supervision of earthworks
1417
96.9 References
1418
Chapter 97: Pile integrity testing
1419
S. French and M. Turner
97.1 Introduction
1419
97.2 The history and development of non-destructive pile testing
1420
97.3 A Review of defects in piles in the context of NDT
1421
97.4 Low-strain integrity testing
1422
97.5 Cross-hole sonic logging
1437
97.6 Parallel seismic testing
1442
97.7 High-strain integrity testing
1442
97.8 The reliability of pile integrity testing
1443
97.9 Selection of a suitable test method
1448
97.10 References
1448
Chapter 98: Pile capacity testing
1451
M. Brown
98.1 An introduction to pile testing
1451
98.2 Static pile testing
1452
98.3 Bi-directional pile testing
1458
98.4 High strain dynamic pile testing
1460
98.5 Rapid load testing
1463
98.6 Pile testing safety
1467
98.7 Simple overview of pile testing methods
1467
98.8 Acknowledgements
1468
98.9 References
1468
Chapter 99: Materials and material testing for foundations
1471
S. Pennington
99.1 Introduction
1471
99.2 Eurocodes
1471
99.3 Materials
1471
99.4 Verifi cation
1472
99.5 Concrete
1472
Chapter 87: Rock stabilisation
1295
R. Nicholson
87.1 Introduction
1295
87.2 Management solutions
1296
87.3 Engineered solutions
1297
87.4 Maintenance requirements
1301
87.5 References
1302
Chapter 88: Soil nailing construction
1303
P. Ball and M. R. Gavins
88.1 Introduction
1303
88.2 Planning
1303
88.3 Slope/site preparation
1305
88.4 Drilling
1306
88.5 Placing the soil nail reinforcement
1306
88.6 Grouting
1307
88.7 Completion/fi nishing
1307
88.8 Slope facing
1308
88.9 Drainage
1310
88.10 Testing
1311
88.11 References
1312
Chapter 89: Ground anchors construction
1313
J. Judge
89.1 Introduction
1313
89.2 Applications of ground anchors
1313
89.3 Types of ground anchors
1314
89.4 Ground anchor tendons
1315
89.5 Construction methods in various ground types
1316
89.6 Ground anchor testing and maintenance
1320
89.7 References
1321
Chapter 90: Geotechnical grouting and soil mixing
1323
A. L. Bell
90.1 Introduction and background
1323
90.2 Permeation grouting in soils
1324
90.3 Soilfracture and compensation grouting
1327
90.4 Compaction grouting
1328
90.5 Jet grouting
1330
90.6 Soil mixing
1333
90.7 Verifi cation for grouting and soil mixing
1338
90.8 References
1340
Chapter 91: Modular foundations and retaining walls
1343
C. Wren
91.1 Introduction
1343
91.2 Modular foundations
1344
91.3 Off-site manufactured solutions – the rationale
1344
91.4 Pre-cast concrete systems
1345
91.5 Modular retaining structures
1349
91.6 References
1349
SECTION 9: Construction verifi cation
1351
Section Editor: M. Brown and M. Devriendt
Chapter 92: Introduction to Section 9
1353
M. Devriendt and M. Brown
Chapter 93: Quality assurance
1355
D. Corke and T. P. Suckling
93.1 Introduction
1355
93.2 Quality management systems
1355
93.3 Geotechnical specifi cations
1355
93.4 Role of the resident engineer
1356
93.5 Self-certifi cation
1356
93.6 Finding non-conformances
1357
93.7 Forensic investigations
1359
93.8 Conclusions
1360
93.9 References
1361
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ice | manuals
100.4 Implementation of planned modifi cations during construction
1497
100.5 ‘Best way out’ approach in OM
1499
100.6 Concluding remarks
1500
100.7 References
1500
Chapter 101: Close-out reports
1503
R. Lindsay and M. Kemp
101.1 Introduction
1503
101.2 Reasons for writing close-out reports
1503
101.3 Contents of close-out report
1505
101.4 Reporting on quality issues
1506
101.5 Reporting on health and safety issues
1506
101.6 Documentation systems and preserving data
1507
101.7 Summary
1507
101.8 References
1507
Index to volumes I and II
1509
99.6 Steel and cast iron
1475
99.7 Timber
1477
99.8 Geosynthetics
1478
99.9 The ground
1479
99.10 Aggregates
1481
99.11 Grout
1482
99.12 Drilling muds
1483
99.13 Miscellaneous materials
1484
99.14 Re-use of foundations
1485
99.15 References
1486
Chapter 100: Observational method
1489
D. Patel
100.1 Introduction
1489
100.2 Fundamentals of OM implementation and pros and cons of
its use
1491
100.3 OM concepts and design
1492
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Section 5: Design of foundations
Section editor: Anthony S. O'Brien
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Figure 51.1 outlines the layout and contents of Section 5
Design of foundations.
Foundation design is usually divided into two broad cat-
egories: shallow and deep, and these categories are also used
here. In modern foundation engineering it is helpful to con-
sider a third category: hybrid. Hybrid foundations have their
own unique features, although their design usually requires an
assessment of both shallow and deep foundation behaviour.
Examples of hybrid foundations include deep ground improve-
ment and piled rafts.
The fi nal set of topics, special issues, include building
on fi lls, the infl uence of global ground movements on deep
foundations, and foundations subject to cyclic and dynamic
loading, including earthquakes.
In common with other sections of this manual, this section
is intended to provide guidance to practising engineers. Given
the enormous breadth of the subject and the vast range of
ground conditions and structures which a foundation designer
may encounter, this section cannot, within the available space,
be completely comprehensive. The intent is to outline:
the f
■
undamental principles of good design practice;
the key mechanisms of ground and ground–structure interaction
■
behaviour which need to be considered;
Chapter 51
Introduction to Section 5
Anthony S. O’Brien Mott MacDonald, Croydon, UK
Figure 51.1 Layout of chapters in Section 5
Design of foundations
Related topics
Context and fundamental
ground behaviour
Sections 1, 2 and 3
Related topics
Site investigation
Section 4
Construction processes
and verification
Sections 8 and 9
Foundation types and
conceptual design principles
Selecting the appropriate
foundation type
Chapter 52
Shallow foundations
Chapter 53
Deep foundations
Special issues
Hybrid foundations
Global ground
movements
and effects
on piles
Chapter 57
Building
on fills
Chapter 58
Pile groups
Single
piles
Chapter 54
Chapter 55
Rafts
and
piled rafts
Chapter 56
Chapter 59
Design
principles
for ground
improvement
Rafts
Strip
and pad
footings
Chapter 60
Foundations
subject to
cyclic and
dynamic
loads
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commonly used design methods;
■
the need to integrate a range of specialist disciplines at different
■
stages of the design process;
and to provide:
references for detailed study;
■
some brief case histories which highlight key issues.
■
A quote from Terzaghi (1936) is particularly pertinent:
Whoever expects from soil mechanics a set of simple, hard
and fast rules for settlement computations will be deeply dis-
appointed…The nature of the problem strictly precludes such
rules.
Hence, it is essential for the foundation designer to think care-
fully about the likely deformation and failure mechanisms
which may occur both during and after construction; then
compile a checklist of questions which need to be considered
and answered.
There have been enormous developments in founda-
tion engineering during the last few decades. Despite these
developments, failures still regularly occur and there are also
numerous examples of grossly overconservative design and
poor construction practice. There are several commercial and
technical factors that can cause these problems. Technically, it
is important to:
(i) Recognise that foundation engineering is a ‘process’, and
that success depends on a series of interlinked activities
during both design and construction.
(ii) Have a coherent approach to ground risk management;
the ‘geotechnical triangle’ is a valuable framework in
this context. An understanding of the site’s history and its
groundwater regime are critically important.
(iii) Have good communication across different design/con-
struction teams.
(iv) Develop a good understanding of ground–structure interac-
tion. It is vitally important for geotechnical and structural
engineers to have early two-way discussions, so that the
overall behaviour of the proposed works are understood.
In particular, the best opportunity for economic founda-
tion design is to set realistic (rather than arbitrary and usu-
ally overconservative) limits on foundation movement.
(v) Have a good awareness of relevant case histories of past
foundation performance, and to carefully assess the rel-
evant parameters for assessing stability – and in particu-
lar, foundation deformation. Sophisticated analysis is not a
substitute for a proper selection of design parameters, based
on well designed and supervised ground investigations.
Chapter 9 Foundation design decisions provides an introduc-
tion to these themes, and these are developed in more detail
throughout Section 5.
Although it is a simplifi cation, it is fair to state that routine
ground investigation and analysis methods can lead to:
(i) overconservative design of foundations in heavily over-
consolidated soils, such as stiff clays;
(ii) unsafe foundation design in normally and lightly overcon-
solidated soils, such as soft clays.
Modern developments in ground investigation and geotechni-
cal analysis can avoid these problems, although these modern
techniques are still under-used across the civil engineering
industry. The chapters in Section 5 highlight some of the devel-
opments which are mature enough to be used more routinely.
It is hoped that Section 5 will stimulate an improvement in
foundation design practice.
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CONTENTS
52.1 Introduction
733
52.2 Foundation types
734
52.3 Foundation selection
– conceptual design
principles
735
52.4 Allowable foundation
movement
747
52.5 Design bearing
pressures
752
52.6 Parameter selection,
introductory comments 754
52.7 Foundation selection –
a brief case history
759
52.8 Overall conclusions
763
52.9 References
763
52.1 Introduction
This chapter outlines the types of foundation that are com-
monly used, together with the key factors which need to be
considered before selecting a particular foundation type.
Foundation engineering requires a working knowledge of:
geotechnical engineering;
■
construction methods;
■
ground-structure interaction.
■
Professor Peck (1962) outlined the three areas of knowledge
that are needed in geotechnical engineering:
(i) a knowledge of precedents, i.e. a knowledge of case histories;
(ii) a working knowledge of geology;
(iii) familiarity with soil mechanics.
In the vast majority of cases, a foundation design is developed
on the basis of an appreciation of the site geology, the nature
of the proposed structure and any particular site constraints.
The role of analysis is then to check that a proposed foundation
design will be acceptable. Although analysis is important it is
just one part of the overall design process.
Many young civil engineers will have some knowledge of
(iii), but it is important that they endeavour to develop their
knowledge of (i) and (ii) above. A knowledge of geology (and
hydrogeology) is critically important, since it enables many of
the risks associated with foundation engineering at a particular
site to be assessed. Simplifying assumptions have to be made
before any analysis can be carried out (this includes sophisti-
cated computer modelling). The site geology and hydrogeol-
ogy have to be considered and understood, as early as possible
in the project. Discussions should be held with an experienced
geologist. Relevant technical literature and, particularly, local
case histories should be reviewed. Once this has been done
then the appropriateness, or not, of certain assumptions inher-
ent in a particular method of calculation can be judged, and the
likely errors associated with the predictions from calculations
can be assessed. A knowledge of case histories is probably the
most important of the three attributes, since this enables the
engineer to have an understanding of:
(i) what has worked, or not, in the past;
(ii) the consequences of particular construction activities on
subsequent performance;
(iii) past performance, against which the reliability of differ-
ent methods of analysis can be compared;
(iv) when a proposed activity is going beyond what has been
attempted before – this will then require a special effort
and expert advice in order to safely develop the design.
A foundation is a structural member and supports a superstruc-
ture. So an awareness of the sources and nature of structural
loads, the structure’s tolerance of foundation movements, and
an understanding of ground–structure interaction is also needed.
Finally, the foundations must be built economically and safely.
Hence, a designer needs to have an appreciation of construc-
tion methods and equipment, in order to develop a design that is
practical to build.
This list of attributes, which a foundation designer needs to
possess, is rather intimidating. The author has not yet come
across the god-like creature who possesses a perfect knowledge
of all these topics. Therefore, fi rst and foremost, the foundation
designer must be prepared to ask questions and discuss these
with other design and construction specialists (e.g. geologists,
structural and material engineers, specialist sub-contractors,
etc.). Good foundation design is usually the result of a multi-
disciplinary team effort, where two-way communications
across the team occur regularly and frequently.
Chapter 52
Foundation types and conceptual
design principles
Anthony S. O’Brien Mott MacDonald, Croydon, UK
The main types of foundation include: shallow foundations (pad, strip, raft); deep foundations
(piles, caissons, barettes) and hybrid foundations (deep ground improvement, piled rafts).
Foundation engineering requires a broad range of skills, from an appreciation of geology
and hydrogeology to structural engineering. The performance of foundations is dependent
not only on how they are designed, but also on how they are constructed. The overall design
process needs to be well managed, to ensure that there are good communications between
different design teams and between design and construction. To provide a framework for
selecting the most appropriate type of foundation, a useful mnemonic is ‘the 5 S’s’:
S – Soil; S – Structure; S – Site; S – Safety; S – Sustainability
The magnitude of allowable foundation movement is a key factor in determining the type,
size and cost of foundations, and this chapter provides guidance on routine limits. Parameter
selection is a common pitfall, and the critical information requirements are described.
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52.2 Foundation types
There are two generic types of foundation: shallow and deep.
Foundations developed on improved ground can be considered
to be a hybrid of both shallow and deep foundations, although
ground improvement design requires additional considerations.
The advantages and disadvantages of different foundation types
are outlined in Table 52.1.
(1) Shallow foundations: these typically comprise pad, strip
or raft foundations; refer to Figure 52.1. Pad foundations,
Figure 52.1(a), may be square, circular or rectangular.
A pad foundation usually only supports one or two col-
umns. Strip foundations (Figure 52.1(b)) are commonly
used to provide support to a load-bearing wall or for sev-
eral closely spaced columns. The length of a strip foun-
dation is much greater than its width. A raft foundation
(Figure 52.1(c)) could support the entire structure or a
substantial part of it. A ‘compensated’ raft (also known as
a ‘buoyant’ raft) is a special type of raft. It includes a void,
thereby reducing the ‘net’ increase in bearing pressure
(section 52.5) on the ground below the foundation. This
will increase the factor of safety against bearing capacity
failure and reduce foundation settlement, compared with a
conventional raft. The structural form of shallow founda-
tions can vary, but pad and strip foundations could com-
prise either mass concrete or reinforced concrete, whereas
raft foundations usually comprise reinforced concrete.
The soil resistance to the loads applied by the structure are
predominantly developed by the near-surface soil below
the base of the foundation. Shallow foundations are usu-
ally constructed using simple excavation plant and general
labour. Tomlinson et al. (1987) gives useful advice on rou-
tine foundation design for low-rise buildings.
(2) Deep foundations: for the majority of routine structures,
deep foundations comprise piles; refer to Figure 52.2.
There are numerous different types of pile, discussed in
Chapter 54 Single piles although piles are usually classifi ed
as either driven or bored. Pile construction is a specialist
activity and should only be carried out by contractors who
have the appropriate equipment and experience.
The layout of pile foundations can vary substantially
from a single pile below a load-bearing column, to a large
number of piles in a group supporting the entire structure,
via a pile cap (which transfers load from the structure
directly into the piles). For a conventionally designed pile
group, it is assumed that the piles carry the entire load.
Deep foundations also include barettes, shafts or cais-
sons, which tend to be bespoke foundations for special
circumstances. Caissons, barettes and shafts typically
have a large diameter or cross-sectional area relative
to their depth in comparison with conventional piles.
Barettes are rectangular in plan, and are installed using
diaphragm-wall construction techniques. Both shafts and
caissons are circular in plan; however, they are usually
constructed by different methods. Shafts could be hand-
dug or excavated using back-actors, with excavation sup-
port installed top-down, using pre-cast concrete rings or
cast-in situ concrete lining. Caissons are usually jacked or
sunk into place using combinations of kentledge, excava-
tion and perimeter lubrication (using bentonite). For both
piled foundations and deep shafts the load transfer to the
ground is via shear along the vertical sides of the shaft or
pile and by end-bearing resistance.
Piled rafts are a hybrid type of foundation with the struc-
tural load being transferred to the soil via the raft (as for a
shallow foundation) and the piles (as for a deep foundation).
The principal difference between a piled raft and a conven-
tional pile group is that the piles are designed to mobilise
most of their ultimate load-bearing resistance and act as
settlement-reducing elements whilst the raft provides the
appropriate overall factor of safety against bearing capacity
failure. Compared with a conventional pile group, a piled
raft has a relatively small number of widely spaced piles
(Figure 52.3). Piled-raft design requires specialist input.
(3) Foundations on improved ground: in general, the pur-
pose of ground improvement is to increase the strength
and stiffness of the ground below a proposed structure,
and then shallow structural foundations are constructed
on the surface of the improved ground (Figure 52.4).
Below the structural foundations, a granular layer (some-
times reinforced with geogrids) is often used to transfer
loads into the reinforcing elements (Figure 52.4). The
mechanism of ground improvement is usually either:
(i) Mass reinforcement – usually for clays, silts or made
ground. A large number of stiff elements are intro-
duced into the compressible layer.
(ii) Densifi cation – usually for sands or gravels. A com-
paction process forces a rearrangement of the soil
particles into a denser state.
Reinforcement: techniques such as vibro stone columns
or deep soil mixing facilitate the replacement of soft com-
pressible materials by stronger materials introduced into the
ground via specialist equipment. These stronger elements
carry most of the foundation load. However, the remaining
soft compressible materials will also carry some of the foun-
dation loads, hence the term ‘reinforcement’. It is important
to note that the reinforcing elements usually have negligible
tensile and bending resistance. Sometimes reinforcing ele-
ments such as stone columns are called ‘stone piles’; how-
ever, this is quite incorrect and misleading. Foundations
built upon improved ground will behave in a quite different
manner to piled foundations (Figure 52.5).
Densifi cation: soils such as loose sand with a low silt or
clay content can be compacted into a denser state. Once den-
sifi ed the sand will be a more competent stratum and be able
to carry the foundation loads directly. Hence, conventional
shallow foundations can be placed on the densifi ed layer.
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Densifi cation may be carried out via a wide range of spe-
cialist equipment. The key issue for densifi cation projects is
usually the relative density that can be achieved compared
with the value which is needed to ensure that foundation
settlement is acceptable.
The success of ground improvement (both by reinforce-
ment or densifi cation) is sensitive to the nature of the soil
profi le and the soil macrofabric. For example, densifi cation
by vibrocompaction may be straightforward if the sand is
homogeneous and has a low silt or clay content. Compaction
will be much more diffi cult and often less effective if there
are numerous bands of silt or clay in the sand. These soil
features can be easily missed by conventional boreholes and
sampling at discrete depth intervals. Continuous sampling or
profi ling techniques (such as static cone penetration testing,
CPTs) are usually very benefi cial when designing ground
improvement. Similar considerations can apply to reinforce-
ment techniques. Quality control and fi eld testing in order to
verify the effectiveness of ground improvement are a signifi -
cant component of any ground-improvement project.
52.3 Foundation selection – conceptual design
principles
52.3.1 Information requirements and the foundation
design process
Figure 52.6 outlines the typical information requirements, the
design deliverables (reports, etc.) and the project phases that
are followed to design and construct a foundation. During the
early stages the key questions are:
(1) Site geology, hydrogeology and history: what are the geo-
logical age and the depositional environment of the main
deposits under the site? What subsequent changes may
have occurred (e.g. landslides, man’s infl uence)?
(2) What will be built?: form of structure, likely construction
methods, main site constraints, applied loads, principal
constraints (e.g. allowable structural movements)?
(3) Engineering knowledge: what existing knowledge do we
have? For example, relevant technical literature, good
case histories, local customs and experience or expertise.
This collation of available data into a desk study report is an
important and cost-effective means of managing ground risks on
a project. Sole reliance on boreholes in the absence of a proper
desk study is potentially very dangerous. The main ground
hazards can be identifi ed from the desk study and the key fea-
tures of ground behaviour can be assessed. This will inform the
design of intrusive ground investigation (refer to Chapters 40 The
ground as a hazard, 41 Man-made hazards and obstructions, 43
Preliminary studies and 44 Planning, procurement and manage-
ment). It is often the case that designers ‘inherit’ ground inves-
tigation reports from previous or adjacent projects and studies.
It is very important that the scope, adequacy and reliability of
this information are assessed in the context of the current project
requirements. If the structure has been relocated, or more oner-
ous loading or allowable movement criteria are required, then an
additional ground investigation may be needed (perhaps using
more sophisticated investigation techniques).
Foundation design is an iterative process. Once relevant
information has been obtained for the site, the key data should
Superstructure
column
Bearing wall
(or multiple
colomns)
Ground surface
Ground surface
(a)
(b)
(c)
(d)
Pad
Strip
Raft
‘Compensated’ raft
Entire
structure
Entire
structure
Void
B
L
B
B
T
D
D
T
Figure 52.1 Types of shallow foundations
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Figure 52.2 Deep foundation, conventional pile group
Figure 52.3 Hybrid foundation, piled raft
Original soil
(uncompacted)
Shallow foundation,
raft or strip foundations
Ground mass, densified
Ground mass, densified
beneath foundations
beneath foundations
Ground mass, densified
beneath foundations
Ground mass,
Ground mass,
reinforced beneath
reinforced beneath
foundations
foundations
Ground mass,
reinforced beneath
foundations
Most of foundation load
taken by reinforcing elements
Lateral confinement
by natural ground (?)
(a) Ground improvement by densification
(b) Ground improvement by reinforcement
Some foundation load
resisted by natural ground
Ground
surface
Ground
surface
Geogrid reinforced
granular layer (?)
Pad/strip
foundations
Competent soil layer
Competent soil layer
Figure 52.4 Hybrid foundation – deep ground improvement
be summarised on a plan and vertical cross-sections through
and beyond the site boundaries. Drawn to scale, with levels
referenced to an appropriate survey datum, as a minimum, the
following features should be drawn:
(i) the previous and proposed ground surfaces;
(ii) any previous and neighbouring structures and under-
ground services;
(iii) ground profi le, strata boundaries (including selected
ground properties from testing);
(iv) groundwater levels;
(v) outline of the proposed structure and proposed locations
for foundations;
(vi) list as bullet points, the key site constraints and hazards.
Based on a knowledge of the ground profi le, the type of struc-
ture and key site constraints, an experienced engineer should
be able to identify appropriate conceptual designs for the foun-
dations. Analyses would then be carried out to check that this
concept had an acceptable level of stability and that foundation
movements were acceptable. If these are not acceptable, then
the concept would be modifi ed (say, pile foundations would
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