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PUBLICATION NUMBER P156

Steel Bearing Piles Guide

A R BIDDLE BSc, CEng, MICE

Published by:

The Steel Construction Institute

Silwood Park

AscotBerkshire SL5 7QN

Telephone: 01344 623345

Fax: 01344 622944

P156: Steel bearing piles guide

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m a t e r i a l i s c o p y r i g h t - a l l r i g h t s r e s e r v e d . R e p r o d u c e d f o r I H S T e c h n i c a l I n d e x e s L t d u n d e r l i c e n c e f r o

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© 1997 The Steel Construction Institute

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Although care has been taken to ensure, to the best of our knowledge, that all data and information

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and the reviewers assume no responsibility for any errors in or misinterpretations of such data and/or

information or any loss or damage arising from or related to their use.

Publication Number: P156

ISBN 1 85942 050 8

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A catalogue record for this book is available from the British Library.


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FOREWORD

The publication Steel Bearing Piles, compiled by G. M. Cornfield in the 1960s, was first published by Constrado in 1970 and later published as the Fourth Edition by The SteelConstruction Institute in 1989. Significant research and development in many aspects of steel piling has since taken place, and it was felt timely to produce this new publication,completely revising the Fourth Edition to cover the subject in more detail.

The guide is laid out in sections which follow the steps involved in a well established design procedure used in current practice for the design of hollow steel tubular piles for offshoresteel platforms and marine works that has been found to be equally applicable to onshorefoundation design and other types of steel section piles.

It is hoped that this new presentation on the subject, with its extensive reference to

investigation and analysis work by other researchers, will provide the necessary confidencefor practising engineers to use steel piling more extensively. Once designers become morefamiliar with the behaviour and advantages of steel piles there should be more innovative useof steel piling applications in structural and building foundations.

An essential part of this project has been the gathering of an SCI database of axial load testson steel H-piles and sheet piles to validate load capacity prediction methods. Partnershipswere formed with SCI members who have provided soils data and load test results from steeltest piles on their construction sites. Their cooperation and time is gratefully acknowledged.

The major partners were: Cementation Piling and Foundations Ltd; DEL Piling Contractors;Devon County Council; Edmund Nuttall Ltd; Humberside County Council; L G Moucheland Partners; North Yorkshire County Council; Stirling Maynard and Partners; SymondsTravers Morgan Ltd; Testing and Analysis Ltd.

Particular thanks is also expressed to the members of the Steel Piling Group who reviewed the draft in detail before the editing phase:

Robert Dunsire Babtie GroupCyril Tuck, Jim Wilson and John Morrisroe British Steel Piling Technical ServicesKen Fleming Cementation Piling and Foundations Ltd David Thompson Dew Group Piling Ltd Peter Crossley Edmund Nuttall Ltd

Mike Horsnell Fugro UK Ltd John Seaman Ove Arup and PartnersBill Mitchell Sir William Halcrow and PartnersViv Troughton Stent Foundations Ltd Eifion Rees Evans Railtrack plc

The Department of the Environment and British Steel plc have funded the preparation of this Design Guide in order to initiate the transfer of knowledge and technology of steel piles from the UK offshore sector to the broader civilengineering industry and thereby to improve the competitiveness of steel piles inconstruction.


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CONTENTSPage No.

FOREWORD iii

SUMMARY vii

Notation xi

1 INTRODUCTION 1

1.1 Piled foundations 1

1.2 Why choose steel piling? 2

1.3 Scope of this publication 4

2 DESIGN BASIS 5

2.1 General 5

2.2 Design standards 6

2.3 Limit state design rules 6

2.4 Geotechnical design methods 11

2.5 Soil resistance on driven steel piles 12

2.6 Load-settlement behaviour - friction piles 13

2.7 Pile-soil load transfer - friction piles 16

2.8 Load settlement behaviour - end bearing piles 16

2.9 Pile-soil load transfer - end bearing piles 18

2.10 Site investigation 18

2.11 Design methodology 20

3 SELECTION OF PILE SECTION 23

3.1 Steel piles in bearing only 23

3.2 Embedded retaining walls 23

3.3 Combined retaining and bearing functions 25

3.4 Selection of steel section 26

3.5 H-Piles 26

3.6 Tubular piles 28

3.7 Sheet piles 30

3.8 Box piles 30

3.9 High Modulus Piles 30

3.10 Combi-piles 33

4 AXIAL LOAD RESISTANCE 34

4.1 Interpretation of soil parameters 34


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4.2 Predictive methods - general 34

4.3 Pile axial movement models 36

4.4 Load resistance in non-cohesive, granular soils 39

4.5 Load resistance in cohesive soils 43

4.6 Load resistance in rock 45

4.7 Negative shaft friction 48

4.8 Measures to increase steel pile axial capacity 49

5 LATERAL LOAD RESISTANCE 50

5.1 Introduction 50

5.2 Methods of analysis 50

5.3 Assessment of soil properties 52

6 PILE GROUP EFFECTS 55

6.1 Conceptual design-vertical load resistance 55

6.2 Methods of lateral load resistance analysis 56

6.3 Practical pile group design 57

7 THE INSTALLATION AND TESTING OF STEEL BEARING PILES 61

7.1 Pile driving installation methods 61

7.2 Offshore experience of pile driving analysis 65

7.3 Driving formulae and dynamic driving resistance 66

7.4 Pile load testing 72

7.5 Steel pile installation tolerances 76

7.6 Environmental factors with driven piles 77

8 STEEL PILE/STRUCTURE CONNECTIONS 80

9 CORROSION AND PROTECTION OF STEEL PILES 83

9.1 General 83

9.2 Corrosion in soil 84

9.3 Atmospheric corrosion 84

9.4 Corrosion below water 85

9.5 Methods of increasing effective life 85

9.6 Corrosion in fills and industrial soils 87

10 REFERENCES 88

APPENDIX A CONTACTS 99


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SUMMARY

This publication gives guidance on the selection, design and installation of steelbearing piles for foundations to all types of structure. Current practice and experience in this field are presented, discussed and recommendations given. The characteristics and advantages of steel bearing piles in construction aredescribed in order to assist in the primary process of selection of the correct piletype for any given site and soil conditions. Load transfer mechanisms aredescribed and limit state design interpreted in relation to measured pile head movements. The sections on design include axial and lateral load resistance

prediction methods, combined loading effects on retaining walls and pile groupanalysis. Up-to-date pile driving analysis is presented as a basis for planningefficient installation and as an aid to design. Practical aspects of test loading,

installation tolerances and connection details are covered.

It is noted that excessive conservatism has been found in current practice and in thecurrently used specifications for load testing piles, which has been compounded by unrealistic design assumptions on the soil parameters that are used in pileresistance prediction methods. Consequently, designers have been unable tointerpret the ultimate pile capacity from their load test results and the whole basisof the new limit state design (LSD) procedures has been denied. This publicationadopts LSD which should permit more economic steel pile design.

Guide des pieux en acier portant par la pointe

Résumé

Cette publication est consacrée au choix, au dimensionnement et à la mise en places de pieux de fondations en acier pour tout type de structure. La pratiqueactuelle est discutée et des recommandations sont données.

Les caractéristiques et avantages des pieux en acier sont décrits afin d’aider auchoix d’un système correct de pieux pour tout site et toutes conditions de sols. Lesmécanismes de transfert des charges sont décrits et les états limites dedimensionnement sont discutés, en liaison avec les déplacements de la tête du pieu.

Les chapitres consacrés au dimensionnement prennent en compte les charges

axiales et latérales ainsi que l’effet des murs en retour et des groupes de pieux. Les méthodes les plus modernes de mise en place sont présentées. Les essais derésistance, les tolérances d’installation et les détails d’assemblage sont également abordés.

Un conservatisme excessif est constaté dans la pratique courante et dans lesspécifications actuelles conduisant à des hypothèses non réalistes dans les méthodesde calcul. Ceci a conduit à des différentes considérables entre les calculs et lesessais de pieux métalliques in situ; avec pour conséquence une grande difficulté,

pour les praticiens, d’interpréter les résultats d’essais, et ainsi toute la base desnouvelles procédures de dimensionnement à un état limite était niée. Cette

publication adopte la méthode des états limites, qui conduit à un dimensionnement plus économique des pieux en acier.


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Stahlpfähle - Ein Leitfaden

Zusammenfassung

Diese Publikation gibt eine Anleitung zu Auswahl, Berechnung und Einbau von

Stahlpfählen für die Gründungen aller Tragwerksarten. Die gegenwärtige Praxisund Erfahrung auf diesem Gebiet wird vorgestellt, diskutiert und es werden Empfehlungen gegeben.

Die Eigenschaften und Vorteile von Stahlpfählen werden beschrieben, um die Auswahl des richtigen Pfahltyps für jede Baustelle und jeden Baugrund zuerleichtern. Die Mechanismen der Lastübertragung werden beschrieben und der Grenzzustand der Tragfähigkeit in Relation zu gemessenen Pfahlkopfverschiebungenwird interpretiert. Die Abschnitte zur Berechnung beinhalten Methoden zur Vorhersage des Widerstands für axiale und horizontale Lasten, Pfahlwände beikombinierter Belastung und die Berechnung von Pfahlgruppen. Neueste

Berechnungen zum Rammen werden vorgestellt als Basis für einen effizienten

Einbau und als Berechnungshilfe. Praktische Aspekte aus Versuchsbelastungen, Einbautoleranzen und Verbindungsdetails werden behandelt.

Übertriebener Konservatismus wurde in der gegenwärtigen Praxis und den Regelungen für Pfahlversuche vorgefunden, verbunden mit unrealistischen Berechnungsannahmen hinsichtlich der Bodenparameter, die bei der Vorhersagedes Pfahlwiderstands verwendet werden. Folglich waren die Ingenieure nicht inder Lage die Grenztragfähigkeit der Pfähle aufgrund ihrer Versuchsergebnisse zudeuten; damit wurde die Basis für die neuen Berechnungsmethoden der Grenztragfähigkeit bestritten. Diese Publikation beinhaltet die Nachweise für denGrenzzustand der Tragfähigkeit, die wirtschaftlichere Berechnung von Stahlfählen

erlauben sollten.

Guida all'uso di pile portanti in acciaio

Sommario

Questa pubblicazione fornisce una guida per la scelta, la progettazione el'istallazione di pile portanti in acciaio per fondazioni di differenti tipi di strutture.

In particolare, a seguito di una analisi critica relativa alla corrente pratica progettuale e al livello delle conoscenze, vengono presentate e discusse lespecifiche raccomandazioni in uso per tali elementi strutturali.

Sono illustrate le principali caratteristiche e i vantaggi delle pile portanti in acciaioin modo da fornire un importante aiuto nella scelta della corretta forma strutturaledella pila in funzione del luogo e del tipo di terreno. Vengono descritti in dettaglioi più significativi meccanismi di trasferimento del carico ed è presentato il metodo

progettuale agli stati limite tenendo in conto anche i movimenti di testata delle pile. Le parti di questa pubblicazione dedicate alla progettazione comprendono anchemetodi di stima della resistenza a carichi assiali e trasversali, considerando inoltregli effetti di azioni combinate o di vincolo delle pareti e l'analisi di gruppi di pile.Un aggiornato metodo per l'analisi delle pile e' presentato come base per unconveniente utilizzo e valido aiuto per la fase progettuale. Sono inoltre affrontatigli aspetti pratici delle prove di carico, tolleranze di istallazione e dettagli dei

collegamenti.


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La corrente prassi progettuale e le raccomandazioni attualmente in uso per l'esecuzione di prove di carico risultano eccessivamente penalizzanti in quantobasate su ipotesi poco realistiche per quanto riguarda i parametri base del terreno.Come conseguenza, i progettisti si trovano impossibilitati ad effettuare una stima

corretta della capacità portante ultima sulla base dei risultati delle prove di caricoe quindi il diretto utilizzo della procedure di progetto agli stati limite (LSD) nonappare conveniente. Questa guida adotta il metodo progettuale degli stati limite al

fine di consentire una progettazione economica di pile portanti in acciaio.

Guía para pilotes de acero

Resumen

Esta publicación guía la elección, proyecto e instalación de pilotes de acero paracimientos de cualquier tipo de estructura. Se presentan tanto la práctica como laexperiencia actuales con su discusión y pertinentes recomendaciones.

Se describen las propiedades y ventajas de los pilotes de acero en la construccióncon lo que se facilita el anteproyecto del tipo adecuado de pilotes para cualquier tipo de suelo. Se describen también los mecanismos de transferencia de cargas ylos estados límites de proyecto interpretados en relación a los movimientos medidosen cabeza de los pilotes. Los apartados relativos al proyecto incluyen métodos de

predicción de la resistencia a cargas longitudinales y transversales, efectos decarga combinada en muros de contención y cálculo de grupos de pilotes. Se

presentan cálculos de hinca, actualizados, para una planificación efectiva de lainstalación y como ayuda de proyecto. También se tratan aspectos prácticos de losensayos de carga, tolerancias de instalación y detalles de uniones.

Se toma nota de que un conservadurismo excesivo ha sido observado en la prácticahabitual y en las normas o recomendaciones utilizadas en el ensayo de pilotes, loque además suele venir combinado con hipótesis de proyecto poco realistas sobrelos parámetros del suelo que se utilizan en los métodos de predicción de laresistencia. Por todo ello, los proyectistas eran incapaces de interpretar lacapacidad última de los pilotes a partir de sus ensayos de carga y ello hizo que el nuevo método de cálculo en estados límites últimos fuese rechazado radicalmente.

Esta publicación adopta el cálculo en estados límites últimos que debería permitir proyectos más económicos de pilotes de acero.

Sammanfattning

Handbok om Stålpålar

Denna publikation ger handledning till urval, dimensionering och slagning avbärande stålpålar för grundläggning av alla typer av byggnader. Aktuellautföranden och erfarenheter på detta område presenteras och diskuteras, ochrekommendationer ges.

Egenskaperna och fördelarna med bärande stålpålar för byggandet beskrivs för vägledning i den inledande processen för val av korrekt påltyp till en given platsoch markegenskaper. Kraftöverföringsmekanismerna beskrivs och bruks- och

brottgränsdimensionering förklaras i relation till pålhuvudets rörelser. Urvalet för dimensionering inkluderar metoder för beräkningar av bärighet under påverkan av


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Notation

The following notation is that given in Eurocode 7: Part 1. The terms most frequently referred to in the text are listed here for ease of reference.

The symbol F c is used here to denote the externally applied compressive load to a pile in order to be consistent with the Eurocode notation for LSD and in place of the symbols Q or P traditionally used in the UK. Other symbols that are used inthis guide are as follows:

Rc ultimate pile resistance in compression Rt ultimate pile resistance in tension Rs ultimate shaft resistance Rb ultimate base resistance

Rm measured axial pile resistance. Rcm measured compressive axial pile resistance. Rck characteristic compressive axial pile resistance. Rsd design shaft resistance Rbd design base resistance Rcd design compressive axial pile resistance. Rtrd design ultimate pile resistance to transverse loading F trd design ultimate transverse load to pile

Other symbols used in the limit state design notation are explained in Section 2where the context will be clearer and easier to follow.


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1 INTRODUCTION

1.1 Piled foundationsThe first decision in considering a foundation design is whether piles are required

or not. In some cases there may be alternative solutions, for which the costs may

be compared with those of a piled foundation. In other cases, the bearing capacity

of the soil at the foundation level may be satisfactory but, owing to high loadings,

piles are required to keep settlement within acceptable limits. It is important to be

clear about the reasons for using bearing piles.

Bearing piles are used mostly for supporting vertical loads and for this purpose the

main requirements are to:

C restrict average settlement to a reasonable amount

C restrict differential settlement

C achieve an adequate factor of safety or load factor against foundation failure.

Many technical and economic factors affect the selection of the most appropriate

type of pile for a given structure. Very broadly, these factors can be divided into

those related to:

C general site conditions

C underlying soil conditions, including the ground water level

C nature and size of the loads to be supported by the foundation

C type of structure, e.g. land or marine

C effect of the pile type on overall construction programme and cost.

In some circumstances there will be additional factors affecting the choice of pile,

for instance when overturning moments due to wind forces on a tall building have

to be resisted, or when severe scouring of a river bed may expose piles supporting

a bridge pier.

Where piles have to resist tensile loading or absorb energy in bending, as in marine

dolphins for ship impact, and in bridge abutments and support piers for vehicle

impact, there are special requirements to be considered which favour the selection

of steel piles.

The considerations which may affect the choice of pile type include:

C total cost of the foundation, where it is important that the comparison between

pile types is related to the total construction cost and not just the cost of

material

C total construction time, where use of driven steel piling can result in shorter

construction and an earlier project completion date

C environmental constraints, where noise and vibration characteristics of piling

during installation must now be within limits stated in UK legislation and the

benefits of reuse of piles and ease of removal weighed up in the whole lifecosts.


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The above factors are clearly interrelated, and all require consideration in arrivingat the most suitable pile type for a given situation. Broad guidance only is possiblein this publication, as each project requires individual examination; for specific

technical advice or product information, the organisations listed in Appendix A of this publication should be contacted. There is no single pile type which is bothtechnically and economically appropriate for every structure, site or set of soilconditions. Owing to the many different situations, there will always be a need fora variety of pile types, so that selection is an exercise of judgement in the best

possible choice.

1.2 Why choose steel piling?

Knowledge of steel bearing piles has progressed over the last 30 years due toincreased usage worldwide, particularly in the USA, Japan and in European

countries including Holland, Belgium and Denmark. Recent research work for theoffshore industry has been carried out and reported in the UK(1)(2)(3) and the transferof this knowledge was considered beneficial for UK onshore application.

The trend towards increased foundation loads is well catered for by steel bearing piles. H-piles and box piles are capable of carrying loads of up to 4400 kN.Tubular piles, available in a wide range of diameters and thicknesses, have load capacities up to 16MN.

Steel piling offers many advantages compared to other types including:

C Reduced foundation construction time and site occupation.

C Reliable section properties without need for onsite pile integrity checking.

C High ductility that can reduce bending stresses and soil reactions.

C Higher end bearing resistance in granular soils and rocks mobilised by piledriving as compared to boring.

C Pile load capacity can be confirmed during driving by Dynamic Pile Analysis(DPA) on each pile.

C Low displacement of adjacent soils during driving.

C Easily removed for site reinstatement.

C Reusable or recyclable following extraction.

C Closer spacing possible

Steel piles have clear-cut advantages on projects such as on river or estuarycrossings where soils are typically granular and waterlogged and unsuitable forsatisfactory pile boring or where soft recent low bearing strength alluvium overliesbedrock. On cohesive soil sites, there is a wide selection of acceptable pile typesand other construction aspects will govern.

Steel piling is today a very much more attractive and competitive alternative for permanent foundations owing to recent research, developments in piling technologyand changes in the construction industry. These can be described under threebroad headings, durability, performance and economy.


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Durability

The subject of corrosion and steel protection has received substantial attention both

in the UK and abroad over the last 30 years. There is now adequate knowledge

on the subjects of corrosion rates, coatings selection and specifications to permit

the designer to make a reasoned judgement on the provision for corrosion prevention. Such information is readily available in the British Steel Piling

Handbook (4), and that general guidance is repeated in Section 9 of this publication

for the sake of completeness. In addition, the corrosion guidance sections of BS

8002(5), BS 6349(6), Eurocode 3: Part 5(7) and the Highways Agency’s BD 42/94(8)

have embodied recent research, and further revisions are in progress.

Performance

Reliable load capacity and driveability predictions are essential for the confident

design and installation of driven piling. These topics have been poorly covered in

most foundation and piling design textbooks and this publication therefore provides

practical advice.

It was deemed appropriate to examine piling technology used in the offshore

construction sector, where there is a body of research and accepted practice, and

to transfer relevant practices to the onshore sector. The offshore design methods

are simple in concept and the principles involved can be readily understood. They

have been used with success in minimising foundation installation costs and the

steel tubular piles have performed well for decades on offshore fixed structures.

These methods are presented in Sections 4, 5 and 6, and supporting references are

given for further detail on usage and applications.

For economic pile design, the methods require knowledgeable judgement of soil

parameters and this, in turn, requires high quality soils data. Such data is

obtainable using routine site investigation techniques, but care must be exercised

in the soil sampling and testing specifications, in order to ensure that

comprehensive data is collected on the soil properties that are relevant to driven

steel piles as well as to bored concrete piles. In particular, there must be more

emphasis on in situ penetration testing (see the advice given in Section 4 on SPT

and CPT soil tests).

Economy

The differential in cost between concrete and steel piling has decreased dramatically

in recent years; the costs of site labour and concreting materials have increased,

whereas the cost of steel has decreased in real terms. In addition, with the advent

of ‘Design and Build’ contracts for civil engineering work, there is more incentive

for innovative design to permit cheaper overall construction by incorporating the

piled foundation into the structural concept rather than leaving it separate.

Constructing in steel permits prefabrication of larger, but still easily erectable, high

quality structural elements that can save construction time; this is an increasingly

attractive project consideration.

In foundations and basements, steel piling that is compatible and easily connectable

to the steel frame of a building can cut overall construction costs. Progress has

also been made in the effective connection between reinforced concrete


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superstructures and steel piling using welded-on shear studs, hoop bar connectorsand careful detailing in composite connections in bridge engineering.

Steel foundation piles are ductile and in many ground engineering applications e.g.

combined retaining wall and axial bearing duty, it is well known that earth pressureforces and bending moments are reduced from the ‘rigid wall’ assumption bydeflection of the wall, thereby producing a saving in structural section.Construction cost savings in basements of up to 40% have been reported bydesigners.

1.3 Scope of this publication

This publication supplements the information given in existing textbooks with up-to-date guidance on those aspects of steel bearing piles that have not beencovered elsewhere.

Section 2 presents a treatment of Limit State Design (LSD) for bearing piles that is consistent with the new Eurocodes and uses the same notation as those standards.LSD is described in a way that relates pile design to the real performance that isobserved in pile load tests, and it thereby permits the designer to understand themagnitude of pile head settlement that occurs in generating pile load resistance.The pile-soil load transfer mechanism is also explained.

Section 3 covers the features of the various available pile types and the selectionof a suitable steel pile section for the intended purpose.

Sections 4, 5 and 6 cover the geotechnical aspects of steel pile design in the context of other design references and textbooks.

Section 7 deals with an up-to-date treatment of pile installation and the testing of steel bearing piles, especially the growing use of dynamic analysis of driving as asubstitute for expensive static loading procedures. The environmental assessment of noise and vibration during driving is also explained.

Section 8 presents some typical connection details for the pile to structureinterconnection and Section 9 covers durability aspects, including a discussion of appropriate corrosion allowances.


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R R

cd

ck

t

=

γ

R R R R

cd cm

t

cm cm= =

×

=

γ ξ 1 3 1 5 1 95. . .

Design resistance based on pile load tests

The ultimate compressive load resistance Rc of a test pile can be obtained from pilehead applied load versus movement measurements. In accordance with the rulesstated in Eurocode 7: Part 1(9), the characteristic compression resistance Rck , i.e.

a “representative minimum” value, is given by:

R R

ck c

=

ξ

The values of the material factor > are given in Table 7.1 of Eurocode 7: Part 1,which is reproduced as Table 2.1 below.

Table 2.1 Values of material factor > from Table 7.1 of Eurocode 7:Part 1 (as confirmed by the UK NAD)

Number of Load Tests 1 2 > 2

a) Factor > on mean R c or R t 1.5 1.35 1.3

b) Factor > on lowest R c or R t 1.5 1.25 1.1

The ULS design bearing (compression) resistance, Rcd , is then given by:

where ( t is 1.3 for steel driven piles, as given in Table 7.2 of Eurocode 7: Part 1,which is reproduced as Table 2.2 below.

Table 2.2 Values of the material factors, ( b , ( s and ( t in Eurocode 7:Part 1 (as confirmed by the UK NAD)

Component factors b s t

Driven steel piles 1.3 1.3 1.3

Bored in situ concrete piles 1.6 1.3 1.5

CFA (continuous flight auger) in situconcrete piles

1.45 1.3 1.4

For a single driven steel pile test result therefore,

Traditional practice in allowable stress design procedure (ASD) has been to use alumped Factor of Safety of 2 for soil resistance, whereas the above shows that limit

state design (LSD), using the partial factor procedure taken from Eurocode 7:Part 1, gives a comparable value of 1.95.


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The effect of the application of these material factors is illustrated in Figure 2.1 using an F c ! * diagram.

0 10 20 30 40 50

Ultimate pile bearing resistance

= R =R +R= the ULS = "failure" load atan uncontrollable settlement.Or the capacity at a settlementlimit of say 40 mm

c

A p p l i e d p i l e l o a d F c

The design working load R= design bearing resistance= inservice maximum applied load

cd

Rcd

Rc

s b

Pile head settlement (mm)δ

2 1 5 3 . v c d

Figure 2.1 Application of limit state partial load and material factors to pile load resistance

It can be seen that application of the material factors > , and ( t places the designworking load on the pile at a level within the elastic range where very little pilehead movement is required, thereby satisfying the SLS criterion for allowablesettlement if set at about 10mm. (It should be noted that the generally accepted limit for settlement for structural spread footings is that of less than 25 mm).

For an unfactored structural load F c, the required pile load resistance is calculated from the expression:

F c × ( fl F cd = Rcm /> × ( t #

where ( fl is a load factor (typically an average of 1.35 using loading according toBS 5400), and therefore Rcm 2.7 F c, which can be compared directly with ASD$

procedure of using a ‘lumped Factor of Safety’ of 3 (2 × a load factor of 1.5).

Design resistance predicted from soil tests

The characteristic ultimate values of shaft friction resistance, Rsk , and of end bearing resistance, Rbk , are representative minimum values determined from therelevant geotechnical prediction methods and appropriate soil parameters (seeSection 4).

The design compression resistance, Rcd , is then given by:

R R R

cd s

s

b

b= +

15 15. .γ γ

where the values of the material factors, ( b, ( s and ( t can be taken from Table 2.2

as before.


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It should be noted that the empirical geotechnical prediction methods are based onload test databases and have to contain conservatively assessed empirical factors,as stated in the requirement in Eurocode 7: Part 1, to ensure that Rck Rm. The#

overall ‘Factor of Safety’ applied in this limit state procedure therefore comprises

a further partial factor contained in the empirical factor that is within the predictionmethod and which allows for the scatter in soil properties and in the load test results. When this is extracted and multiplied out, the total Factor of Safety when

using soil tests to predict the pile load resistance is prudently much greater than 3.

Design resistance for piles end bearing into rock

Where the ground conditions at the site include an underlying rock stratum withina driveable depth, the only reliable method for the designer to determine the

ultimate load capacity is to carry out a pile load test.

The same framework of design rules apply as for soils, except that the endbearing

resistance from the rock at the base will dominate. Even if there are overlyingsoils, the elastic compression due to applied load on the pile will be so small, dueto the high stiffness of the base resistance, that much of the potential frictionalresistance on the pile shaft cannot be mobilised.

The use of the ‘nominal allowable’ rock bearing pressures that are given, forexample, in BS 8004(15), page 11, or in the API Code RP2A (11), such as 10 MPaor 15 MPa, will greatly underestimate most rock resistances and lead to

uneconomic designs. This is because such ‘limit’ judgements were made forspread footings, and the extension of that bearing capacity theory to deep bored cast in situ piles in clay is not often relevant to driven steel piles. Furtherinformation is given in the CIRIA Report: Piled foundations in weak rock (21) to be

published in 1997.

There are no current generic geotechnical design methods available for steel pilesend-bearing into rock that permit a reliable prediction of ultimate capacity to bemade (due to the lack of coordinated research) and therefore the approach by thedesigner should be one of ‘site specific research’. Due to the high variability of rock types in the UK, such an approach is always the most prudent in any case.The ultimate design resistance of steel driven piles in rock is often governed by theallowable stresses in the pile material.

Steel bearing piles are ideally suited to such ground conditions because noexcavation is required, as with bored piles, and any variations in peak load or inthe degree of weathering can be accommodated by varying the driven length.Their low displacement also ensures penetration to a sound layer.

SCI’s database of steel pile load tests, reported in Validation of vertical load capacity prediction methods for steel bearing piles(22), includes some tests with end bearing into rock, and those results together with current accepted practice fromvarious sources are given in Section 4.8.

The basic recommended procedure is to plan the site investigation to include soil penetration testing (SPTs and CPTs) which will help to differentiate the weathered rock layers from the intact rockhead levels. From offshore experience and

European experience with the CPT, it is known from pile driving back-analysis and static load testing that the CPT ‘qc’ value can be assumed as an ultimate unit


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vertical bearing pile is required the designer is recommended to follow theguidance given in CIRIA Report 103 The design of laterally loaded piles(13) and thetextbooks by Poulos and Davis(23), and Tomlinson(24). Guidance on pile groupeffects is given in Section 6.

2.4 Geotechnical design methods

Soils are characterised as either ‘clays/cohesive’ or ‘granular/noncohesive’ types inorder to separate their two fundamentally different behavioural responses to applied

pile load. The generic formulae used to predict soil resistance to pile load includeempirical modifying factors (see Section 4), which can be adjusted according to

previous engineering experience of the influence on the accuracy of predictions of changes in soil type and other factors such as the time delay before load testing.

It will be shown in Section 2.6 that the mechanisms of axial load transfer involved

in shaft friction Rs and base resistance Rb are completely different. The separate prediction of shaft friction and base resistance therefore forms the basis of all‘predictive’ calculations of pile load carrying capacity. The basic equations to be

used for this are written as:

Rc = Rs + Rb - W p (2.1)

and,

Rt = Rs + W p (2.2)

where W p is the weight of the pile.

There is a move towards applying reliability criteria to evaluate structural design procedures in construction, but care should be taken in applying these togeotechnical methods. Many geotechnical design methods rely on averaging soil

properties over the length of a pile, and practitioners have found that simpleformulae can be used with confidence to represent soil response to applied load,

provided that knowledgeable judgement is applied to the selection of the soil parameters involved.

The crucial skill involved is the ‘knowledgeable judgement’, because there is usually such a wide variation in soil strength and properties within a site that it

defies use of a precise interpretive formula. Statistical analysis procedures for soilspatial variables are not relevant either, because many of the soil response parameters are also time-dependent.

The refinement of geotechnical design methods is difficult to justify because of theconsiderable scatter in all pile load test databases that compare Rm to Rc, and thisindicates that our knowledge of soil-pile interaction and the ways in which weapply it are, as yet, imprecise (see Section 4.1). It is therefore preferable that eachformula involves as few variables as possible, to permit designers to appreciate‘cause’ and ‘effect’ during the analysis of problems and thereby to aid their

judgement.


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2.6 Load-settlement behaviour - friction piles

The settlement of a pile head resulting from progressively increasing compressiveload in maintained load stages, i.e. effectively a series of static loadings on the

pile, can be represented as a pile ‘load-settlement’ curve, or an F c

! * diagram,such as that shown in Figure 2.2.

B

0 C

Initial loading

Unloading

P i l e h e a d a x i a l c o

m p r e s s i v e l o a d ( F

)

DRc

c

Pile head vertical settlement ( )δ

Reloading

A

Figure 2.2 Axial load-settlement for a friction pile (F c - * ) curve

The load settlement response is composed of two separate components, the linear

elastic shaft friction Rs and the highly non-linear base resistance Rb (see Equation2.1). These are shown diagrammatically in Figure 2.3.

2.6.1 Linear elastic response of pile

Initially, the pile-soil system behaves in a linear-elastic manner up to some point A on the F c ! * diagram in Figure 2.2. Applying load to the head of the pile

produces axial strain in the steel pile shaft wall and a corresponding downward movement with slippage at the pile wall /soil interface.

Load transfer occurs in the form of shaft friction that at any level on the pile hasan elastic-perfectly plastic load-displacement relationship (see Figure 2.4 for load

in pile due to shaft friction resistance).

Hence the upper part of the pile’s shaft compresses and transfers load to the uppersoils and if the load is released at any stage up to this point, the pile head willrebound elastically to its original level as the shaft steel relaxes (see Figures 2.5and 2.6 for examples of pile head load-displacement relationships from load teststhat demonstrate the repeatability of this phenomenon). No endbearing is mobilised

up to this point A.


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0

Pile head vertical settlement ( )

R

Rb

s

P i l e h e a d a x i a l c o m p r e s s i v e l o a

d ( F )

Base resistance

Shaft resistance

c

δ

Figure 2.3 Components in (F c - * ) curve

1100 10 20 30 40 50 60 70 80 90 100

Movement (mm)

L o a d t r a n s f e r ( k P a )

-50

300

0

50

100

150

200

250

Penetration m

14

15

16.358

17.6

Figure 2.4 Load in steel pile wall at different levels due to shaft frictionresistance (as measured in LDP tests, Paper 13 pg 297,Clarke et al (1) )

2.6.2 Elastic-plastic response of pile

The onset of nonlinear behaviour at point A in Figure 2.2 is associated with thedevelopment of base or end bearing resistance Rb as the load strain in the shaft reaches the pile base level and the lower end of the pile starts to move downwards.Further movement will lead to the mobilisation of full shaft friction Rs by some

point B. If the load is released at this stage, the pile head will rebound to some point C, the amount of ‘permanent set’ being the distance OC, which is mostly theirrecoverable settlement of the pile base sustained in generating a proportion of thebase resistance () Rb), the shaft friction movement being, as explained, an

elastically recoverable component. The latter phenomenon is illustrated in Figures2.5 and 2.6.


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It should be noted that a small residual compression force may remain in the pilewall after unloading, as measured in pile load tests (see Clarke et al(1)), especiallyfor long piles and where the proportion of friction is high. This residual load may

cause a corresponding small contribution to the irrecoverable pile head settlement.

Figure 2.5 Example pile head load/displacement relationship for repetitive loading in a normally consolidated clay (asmeasured in LDP tests, Pentre site, Paper 13, pg 283, Clarkeet al (1) )

Figure 2.6 Example pile head load/displacement relationship for repetitive loading in an overconsolidated clay (as measured in LDP tests, Tilbrook Grange site, Paper 13, pg 283, Clarkeet al (1) )

The pile head settlement required to mobilise the full shaft friction Rs is comparableto the elastic compression of the steel wall, i.e. only of the order of 7 mm to10 mm for piles of typical length 15 m to 20 metres.

The full base resistance of the pile Rb requires a greater settlement for itsmobilisation, and the amount of movement is related to the size of the pile basearea involved. For unplugged steel piles this will depend on the wall section

thickness or in the case of fully plugged piles, upon the diameter or full base widthof the pile. For H-piles or sheet piles, the movement may be 2 to 3 times the steel


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pile wall thickness (i.e. 30 to 40 mm) to generate the wall tip bearing resistance(see page 152 of the ICE Specification for piling and embedded retaining walls(20)).For a fully plugged pile on the other hand, * OC on Figure 2.2 may be of the orderof 10% of the base diameter or width, depending on the soil type. See Section 4

for further discussion on when to assume plugging.Note that if the pile base is in dense sand or rock, the end bearing may bedeveloped with negligible base settlement and the compression of the pile shaft maybe insufficient to mobilise the full potential shaft friction (see Section 2.8).

When the stage of full mobilisation of the base resistance or ultimate baseresistance Rb is reached (i.e. at some point D in Figure 2.2, the pile will settle at an increasing rate under only very small further increases of load (near to the‘ultimate pile capacity’ asymptote). Extended loading periods during pile testsindicate that it is very difficult to achieve the ultimate axial compression resistance,because the curve becomes virtually flat, and to reach the asymptote requires very

large settlements, (see Figure 2.1). However, a pile load test in soil should aimto achieve within about 5% of that value and accepted practice for friction piles isthe load resistance reached at a tip movement of about 30 to 50 mm.

2.7 Pile-soil load transfer - friction piles

The process of driving a steel pile in clays and sands produces a thin layer of completely remoulded soil adjacent to the pile shaft wall that acts as a ‘slip’ and load-transfer layer; its behaviour is now well understood as a result of research ontrial piles (Reference Tomlinson(25); and Clarke et al(1)). If strain gauges areinstalled at various points along the steel pile shaft, the compressive load remainingin the pile can be measured at each level; the distribution of load in the pile isfound to be in the form of that shown in Figure 2.7 (which shows the transfer of load from the pile to the soil at each stage of loading identified in Figure 2.2).

Thus when loaded to point A in Figure 2.2, the whole of the load is carried byskin friction on the pile shaft and there is no transfer of load to the base of the pile(Figure 2.7(a)). When the load reaches point B, most of the pile shaft friction ismobilised and the pile base has started to feel load (Figure 2.7(b)). At point D,there has been no further increase in the load transferred in wall friction but thebase load will have reached its maximum value (Figure 2.7(c)), i.e. the ‘ultimate

pile bearing capacity’ is reached, beyond which the pilehead will move down

vertically under nearly constant load.

2.8 Load settlement behaviour - end bearing piles

If the pile base is in dense sand or rock, the base or end bearing resistance can bedeveloped with very little base movement and the compression of the pile shaft isoften insufficient to mobilise the full potential shaft friction resistance in the soilsoverlying the rock layer.


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Load on headof pile F

c

c

R sRb

c

'ULS deflectionfailure' loadon pile F =R c

Fc

Full shaft frictionresistance R

R∆

Full baseresistance R

(c) F =R =R + Rc c s bc(a) F = R∆ (b) F =R + R∆

s

s bs

b

Base reaction R <R∆

bb

Base ofpile

s

(a) Load in pile at point A on load-settlement curve in Figure 2.2

(b) Load in pile at point B on load-settlement curve in Figure 2.2

(c) Load in pile at point D on load-settlement curve in Figure 2.2

Figure 2.7 Compressive load transfer (pile to soil) from shaft and base

Often the pile head moves only due to elastic compression of the steel wall up tothe predicted ultimate pile load capacity since there is negligible ‘set’ at the base,see Figure 2.8. The total pile head movement will obviously be dependent on the

pile length required to reach the rock or other dense bearing stratum.

0

P i l e h e a d a x i a l c o m p r e s s i v e l o a d ( F )

Rc

c

A

B

C

<10 mmδPile head vertical settlement ( )δ

2 5 1 0 . V C D

Figure 2.8 Pilehead load-settlement curve for an ‘end-bearing’ pile


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respect, soil tests are therefore required to provide the properties relevant to predicting the response of soil to the various phases of construction, namely:

C Pile driving.

C Pile loading during construction.

C Pile static loading during working life.

C Pile live loading (transient) during working life.

2.10.1 Soil test data for design

Granular soils

In situ soil testing should comprise the use of the following:

C The Standard Penetration Test (SPT) as specified by BS 1377: Methods of test for soils for civil engineering purposes: Part 9: In situ tests (26), is a

universal test applicable to all types of granular soil for which it has beenextensively calibrated for the prediction of pile driving resistance, shaft friction and endbearing correlations.

C The Cone Penetration Test (CPT) also specified by BS 1377: Part 9(26), hasbeen extensively calibrated against steel pile design parameters in fine grained granular soils (sands, silts and clays).

C The dilatometer, used to determine the in situ earth pressure coefficients and confined modulus of soils for use in estimates of lateral soil resistance toapplied displacement or force.

C The pressuremeter, used extensively in France and increasingly being applied in the UK to derive in situ soil properties relevant to driven piles.

Laboratory testing should include:

C Saturated and unsaturated bulk densities (unit weight).

C Shear box tests to determine the angle of internal friction (N N).

C Particle size distribution classification tests.

Cohesive soils

For cohesive soils the geotechnical pile design and resistance prediction methodsfor axial loading generally rely on correlations of pile behaviour with the undrained

cohesive strength c u, but care should be taken to select the soil strength at aconsistent strain to failure. This has been addressed in Norwegian and offshorespecifications for triaxial soil testing and is taken as the strength at failure or at astrain of 4%, whichever occurs first.

For lateral loading and retaining wall design, the geotechnical methods for limit state design now require the following deformation and stiffness properties:

C Young’s Modulus ( E 50 and initial tangent modulus).

C Poisson’s ratio.

C Coefficients of subgrade reaction and horizontal subgrade reaction.

and also, for earth pressure calculation:


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C Coefficient of Earth pressure at rest, K 0.

C Coefficients of Active and Passive Earth pressure ( K a and K p).

C Consolidation and permeability characteristics.

2.10.2 Selection of soil parameters

As mentioned in Section 2.4, many geotechnical design and prediction methodsrequire the judgement of average soil parameter values for each soil layer. Thisinterpretation requires experience because there are several processes involved inmaking the judgement, including:

C Classifying and characterising the soils and selecting soil layers.

C Selecting the soil properties that are best suited to the type of soil and thegeotechnical pile design or resistance prediction method that is most appropriate to that type of soil.

C Collating and interpreting the soils data, including checking the validity of each datapoint, e.g. a c u soil strength value, because some may be too low ortoo high for various reasons and may therefore not be representative of thesoil layer.

The designer should ensure that an engineer with relevant geotechnical experienceand knowledge of steel pile design and performance is involved in this judgement

process at the concept design stage, otherwise uneconomic or unsafe judgementsof soil parameters may result.

2.11 Design methodologyObtaining the soil data at the site and the loading data for the project is the

prerequisite for design.

In the first stage of the structural design of a steel bearing pile, the first step is todetermine the required cross-section based on a factored yield strength accordingto the axial and shear loading that it is required to carry, assuming in the structuralanalysis of the building that there is a pinned joint at the connection with the pile.The next step is to choose a pile section shape that will give the required ultimatecapacity by a combination of shaft friction and end bearing to suit the soilconditions at the site. An allowance for loss of section due to corrosion should then

be made according to the required design life (see Section 9) to arrive at a suitablesection size.

The second stage is to determine the length of that pile section that is required togenerate a factored soil resistance to the factored axial load using an appropriategeotechnical prediction method and the soil tests at the site (see Section 4).

The third stage is to assess the practicality of installing such a pile to the depthrequired using available driving hammers by using a wave equation programmesuch as GRLWEAP(27) for a more precise analysis, or using a pile driving formulasuch as Hiley(28) or Janbu (see Section 7) for an approximate check.


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For friction piles, the desireability of changing the cross section to adjust the lengthcan then be judged from sensitivity analyses of various situations to optimise thegeometry in relation to driveability, availability from stock, road transport to site,site installation and connections considerations.

For end-bearing piles, the provision of using a driving shoe might also be evaluated in order to achieve penetration into a sound stratum whilst avoiding local bucklingof the pile base (see Figure 3.2 for typical examples). Dependent on the pile crosssection, this may affect the available skin friction on the remainder of the pile bycausing additional disturbance.

The fourth stage is to assess the possible bending stresses that the pile may attract with various possible connections to the structural foundation (see Section 8). If this is significant, a global analysis of the whole foundation (or at least the critical

pile group) may be required (see Section 6), in order to apportion the moment between each pile in the group. Each pile will then need a lateral loading analysis,

in order to check that the cross section is adequate to take the combined stressesat all levels down the pile according to the pile lateral deflection and the stressesinduced, (see Section 5). Fully corroded section properties should be used for theend of design life condition and comparison to the corrosion allowance profile withdepth will be required to determine the governing combination for the pile section.

If the pile cross section has changed, then a new pile length will have to beobtained from a further geotechnical design and the driveability should be checked anew.

The fifth stage is to evaluate the economic and construction programme effects of

different pile types and configurations and types of connection before selecting asolution and moving onto final detailed design of the connection between pile and structure.

As explained in Section 2, the generation of soil resistance requires pile movement.The new limit state design procedures involve estimation of pile axial and lateralmovements in order to satisfy SLS criteria. The lateral deflection profile willobviously be affected by any change in steel section or pile length.

Figure 2.10 shows a flow diagram for this pile design procedure.


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Integral steel bridges: design of a single-span bridge - Worked Example where thevertical load resistance was found not to be the governing factor.

W

Excavation level

Assumed lengthof wall providingwall frictionresistance

Pile tip

Figure 3.2 Length of sheet pile contributing to wall friction

Embedded steel sheet pile retaining walls have been used in combined loadingsituations such as highway bridge abutments for several decades and there has not been any sign of excessive movements or unsatisfactory performance. Therefore,the current design procedures as described herein can be concluded to besatisfactory.

3.4 Selection of steel section

Steel piles are selected on the basis of overall geometry to suit the geotechnicalrequirements and wall thickness to suit the load, material strength and the drivingstresses to be sustained.

Steel sheet piling, including sections for box piles are produced in accordance withBS EN 10248(45), to grades S270GP and S355GP. Universal beams (for HighModulus Piles) and other plates and sections are produced to BS EN 10025(46),Grades S275 and S355. Steel tubular piles are produced as linepipe to API 5L(47)

Grades X52 up to X80.

3.5 H-PilesSteel H-piles are very efficient in providing a large surface area for generatingshaft friction resistance. For example a 305 mm × 305 mm × 110 kg/m H-pilesection has an external surface equivalent to a concrete pile of diameter 601 mmand a displacement volume only 5% of that of the concrete pile, which enables it to be driven with less energy and into more dense soils. The displacement volumesof British Steel’s range of 305 mm × 305 mm piles cover a range of 3% to 8%of that of equivalent concrete piles. In any given foundation plan area therefore,a greater number of steel H-piles can be provided in a group with a standard spacing of 2B (or 2Dia.) than concrete piles and either the load supported can begreater or, if soil conditions permit, the driven steel piles can be shorter to support

a given structural load. The stiffness of H-piles is different on each orthogonalaxis, allowing designers to select the orientation necessary to achieve the most


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break through debris, scree, dense gravel and boulders, weathered rock surfaces;to seat the pile tip into sloping rock with a toothed key to prevent the pile sliding;to increase the bearing area; and to prevent local buckling damage to the pile tip.

3 1 5 8 . v c d

Figure 3.3 Examples of toe protection shoes for steel H-piles

It should be noted that the provision of such shoes to piles can result in a

significant loss in skin friction resistance in the soil layers overlying the rock orhard stratum due to ‘overcoring’. See also comments in Section 4 on thedevelopment of endbearing and skinfriction in terms of the pilehead movementsrequired.

3.6 Tubular piles

Tubular piles have been used as foundations for offshore steel frame structures forover 70 years, since oil platforms were first required in the oil fields of LakeMaracaibo in Venezuela in the 1920s. Initially, spare oilpipe was used out of convenience but, as the supporting structures became more sophisticated, the cold rolling of piles in structural plate to project-specific diameters and wall thicknessesbecame more common.

Purpose rolled tubular piles are particularly expensive, but high quality steellinepipe that is perfectly suitable for piling is available throughout the EU at reasonable cost. British Steel manufacture such pipe up to 42 in. (1067 mm)diameter at their new Hartlepool linepipe mill and can fabricate project-specificsizes at their Stockton-on-Tees mill.

Linepipe is of course manufactured to a different material specification to that forstructural steel, but its properties are suitable for most structural applications as

well. The cold-rolling process produces consistently higher yield strengths thanthose of hot-rolled steel products and this can have significant benefits for highlyloaded bearing pile and structural column-pile applications, and can permit harderdriving.

The most arduous criteria for the selection of a section are often theaccommodation of high driving stresses during installation and the resistance tolateral loading shear forces in service without inducing plastic deformation in thesection. The different ratio of f y to f ult , however, has to be allowed for in the

partial factors used in limit state design procedures.


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Steel tubular piles have a high stiffness and are therefore also suitable for siteswhere it is necessary to transfer bearing loads into buried rockhead. An exampleof a protective shoe for driving into rock is given in Figure 3.4.

3 1 6 1 . v c d

Figure 3.4 Example of a protective shoe for tubular piles

The range of linepipe sizes as produced by British Steel in 1996 is shown inFigure 3.5.

50

45

40

30

20

10

35

25

15

5

0 0

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

API 5L X52

API 5L X65

API 5L X70

API 5L X80

16 18 20 22 24 26 28 30 32 34 36 423840

Outside pipe diameter (ins)

W a l l t h i c k n e s

s

(mm) (ins)

Figure 3.5 British Steel available range of linepipe

3.7 Sheet piles

Steel sheet pile section walls are increasingly used for bearing pile applications and in combined loading situations. As a result of progress that has been made in

understanding soil resistance and wall behaviour, new design methods are presented in Section 4 of this publication. New applications for permanent sheet pile walls


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3.10 Combi-piles

Combi-piles are another form of part-fabricated piling used to form walls of deepexcavations. The wall is formed from alternating tubular and sheet piles as shownin Figure 3.7. The number of sheets between the tubes varies dependent on therequired section modulus.

1220dia. x 16mm thk. steel tubes

Larssen sheet piles

Figure 3.7 Typical part of a combi-wall

Tubular piles are available in a wide variety of sizes, and both Larssen and Frodingham sheet piles are suitable as infill piles. Appropriate clutches are welded to the walls of the tubes and these provide the designer with simple corner detailsfor many different wall angles. It is apparent that the clutch locking bar stripsfrom U section sheet piles (or Larssen sections) are more stable to weld onto thetubulars than those for Frodingham section sheet piles.

The size and weights of the two types of pile (tubular and sheet) are significantly

different and usually require two different types of plant for driving.

The pitch and drive method of piling is possible for combi-piling, but may not provide sufficient positional accuracy for some sites and applications.

The preferred driving method is to drive the tubes first. This has the advantagethat only one type of driving plant is required at any one time. The positionalaccuracy demanded for the tubular pile driving depends on the number of sheet

piles used between each tube, as the cumulative tolerance is derived from thenumber of clutch connections available.

Once the tubes are in position, the infill sheets are driven in between. In order todrive the sheet piles successfully, the positional accuracy of the tubular piles must be of the order of ±20 mm. Where single sheet piles are used, the reduced cumulative tolerance will require greater accuracy.

In order to achieve this high control in position of piles, a piling frame is essential.This frame is positioned to the required tolerance and subsequently the piles aremonitored for verticality during driving. The tubular pile is held in place in theframe by a system of fixed rollers. If several sets of rollers are provided on theframe at the correct spacing interval, then several tubes can be pitched and drivenwithin each frame. This has proved to be a successful driving technique on severalsites including the Medway Tunnel in Kent.


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It is evident that pile design methods only make significant progress and becomewidely accepted as a result of well organised and well publicised pile load testing,as was the case with large diameter bored concrete piles in the 1960s.

Tubular steel piles are always used for supporting tubular steel offshore frame production platforms, and the Offshore Oil and Gas Industry collectively funded full scale loading tests on 762 mm OD tubular piles in the 1960s and 1980s whichhas progressed the knowledge of pile behaviour in both sands and clays. Thisresearch has included:

C Instrumented pile load tests in both granular and cohesive soils.

C Improved soil investigation methods and tools for soil strength definition, e.g.Dutch cone penetration tests (CPT); push sampling; piston sampling; T-Z

probe.

C Analysis of pile behaviour and calibration of design prediction methods.

C International pooling of knowledge and best practice.

Data from two major load test programmes on steel piles in UK clays was released into the public domain via a conference at the Institution of Civil Engineers in 1992(ref. Clarke et al(1)). Load testing on sand sites in Holland, Belgium, France,Denmark, and in the UK has been interpreted and reported in 1996 by ImperialCollege (ref. Jardine et al(3)).

This has resulted in a consensus amongst practising experts in the offshore industryas to the best soil resistance prediction methods to use for tubular steel piles. Themethods have a sound theoretical basis, but the limitations of theory are recognised by including empirical adjustment factors. These methods are accepted in the

offshore design codes in the USA, namely the American Petroleum Institute (API)Code for the Design and Construction of Offshore Structures (RP2A)(11); in the UKalso by BS 6235(49); and by the draft ISO Code 13819(12) which is currently beingdeveloped.

These methods are equally applicable to onshore tubular steel piles and are detailed in Sections 4.4 and 4.5. They have now also been validated by SCI against theresults from a load test database(22) of H-piles and sheet piles. Collation and analysis of pile axial load tests on steel H-piles and sheet piles in both granular and cohesive soils in the UK has been carried out by the SCI in 1996 and 1997 in orderto clarify the manner in which they can be applied and the level of confidence. It

was found that the full area of the pile shaft should be used (i.e. 2D+4B for anH-pile as shown on Figure 4.1) and that ‘plugging’ is very rare and should not beassumed unless it is demonstrated to be developed during driving. The conceptsor ‘models’ that can be used with confidence as a basis to calculate the pile load resistance from soil tests are as shown below in Figure 4.1.

The SCI validation work also included other predictive methods such as the SPTand CPT methods for granular soils, to evaluate their relative reliability.Interpretation of the database(22)(29) forms the basis of the recommendationscontained herein.


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t/t

0.250.500.750.901.00

max z/D

0.0020.0130.0420.0730.100

Q/Q = 1.0p

z = 0.10 x pile diameter (D)u

Pile head vertical movement, ratio z/D 2 1 1 5 . v c d

Figure 4.2 Pile axial load transfer/movement curves, end bearing (Q-Z)(Source: American Petroleum Institute, Code RP2A)

0 0.02 0.03 0.04 0.05

maxt = f

t = 0.9 fmaxRES

maxRESt = 0.7 f

0.01

Sand

Clay

0

1.0

0.8

0.6

0.4

0.2

t/t max

0 0.1 0.2 0.3 0.4 0.5

z/D

z/D

0.000.00160.00310.00570.00800.01000.0200

t/t

0.000.300.500.750.901.00

0.70 to 0.900.70 to 0.90

max

t/t

0.001.001.00

max

Clay: Sand:

Range of tfor clays

RES

z

0.000.10

Pile head vertical movement, z (inches)

2 1 1 6 . v c d

D = pile diameter or pile base width assuming full plugging

t = wall friction resistance on pile shaft

Q = partial end-bearing resistance on pile cross section

Qp= maximum design end bearing resistance on full pile cross section

Z = pile head vertical displacement

Figure 4.3 Pile axial load transfer/movement curves, shaft friction (t-Z)

(Source: American Petroleum Institute, Code RP2A)


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8 mm

35 mm

Loading

0 50 100 150 200 2500

10

20

30

40

50

Test load - tonnes

A

P

QD

C

B

H e a d s e t t l e m e n t i n m m

233220

Unloading

Figure 4.4 Typical pile head load-settlement curve

Onshore full scale pile load testing on steel piles of various cross-sections on manysites has verified that a vertical pile head deflection of 7 to 10 mm is all that isrequired to generate the full predicted wall friction resistance along the length of most piles (see Clarke et al(1), Jardine et al(3) and Biddle(22)).

Pile head movement at the point of ultimate load resistance is typically 30 to

40 mm, as shown on Figure 4.4. Permitted pile head movement in practice isrestricted by the application of load and material factors in LSD and lumped factorsin ASD (see Figure 2.1), and the settlement of the pile head will therefore belimited to less than 10 mm at its design resistance Rcd when derived in accordancewith Section 2.3.

This magnitude of ‘settlement’ is well within structurally tolerable limits for most structures, especially since the major portion of vertical load for onshore structuresis the deadweight of the structure and therefore occurs during the construction

period and is confidently predictable if pile load tests are performed at the site.

Steel piles that derive the major portion of their load resistance in end bearing aregenerally those driven into rocks or dense granular soils where the end bearing ‘Q-Z stiffness’ will be high and will dominate. In such piles it will be necessary tolimit the design load resistance by consideration of local buckling near the tip.This can be determined from trial pile load tests at the point of departure fromelastic behaviour of the F c ! * curve (see Figure 2.2 and validation testing reported by Biddle(22)(29)). Pile head movements in such ground conditions are small (of theorder of 2 to 4 mm and generally less than 10 mm) and therefore well withinstructurally acceptable levels.


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4.4 Load resistance in non-cohesive, granular soils

4.4.1 Prediction from soil tests - API method

Shaft friction

For tubular steel piles according to the offshore API RP2A code, the ultimate

frictional resistance on a pile shaft Rs in cohesionless, granular soils for eachsoil layer can be estimated using the formula:

Rs = K s poN tan (* ). ! s

where K s = coefficient of lateral earth pressure against pile shaft wall

poN = average effective overburden pressure over soil layer

! s = Exposed area of pile shaft in the soil layer

N ’ = average angle of internal friction within granular soil layer

* = effective interaction friction angle between the pile wall and the soilin the soil layer, which is equal to (N Nlaboratory - 5E).

The method has been investigated in an SCI Technical Report (22) and found to bevalid for H-piles and sheet piles provided that the whole steel surface area is used and that there are sufficient laboratory soil tests to determine the N ’ values for eachlayer.

Table 4.1 gives typical N ’ values for different types of granular soil.

Table 4.1 Typical N ’ values for granular soils (taken from API RP2A)

Density Soil

description

Soil - pile

friction

angle (o)

Limiting skin

friction values

(kN/m2=kPa)

N q Limiting unit

end bearing

values

(MN/m2=MPa)

Very loose

Loose

Medium

Sand

Sand-Silt

Silt

15 47.8 8 1.9

Loose

Medium

Dense

Sand

Sand-Silt

Silt

20 67 12 2.9

MediumDense

SandSand-Silt

25 81.3 20 4.8

Dense

Very dense

Sand

Sand-Silt

30 95.7 40 9.6

Dense

Very dense

Gravel

Sand

35 114.8 50 12.0

Base resistance

For tubular steel piles according to the API RP2A code, the ultimate pile end

bearing Rb in cohesionless soils can be estimated using the formula:

Rb = poN N q Ab


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Unit shaft friction = 0.35 f s

End-bearing

For plugged steel pile sections the ultimate unit endbearing is estimated from thecone values after applying Schmertmann’s averaging process for q

c values above

and below the pile toe, and then adopting limits (see Reference 52). This will produce a conservative prediction of pile capacity that will limit pile settlement.However where plugging is suspected, static pile load testing should always becarried out to confirm the design assumptions.

For unplugged steel pile sections, the qc value at any level can be used directlywithout modification as the ultimate unit endbearing resistance pressure under thesteel wall area. This resistance also applies to the tip of the pile during driving.

4.4.4 Conclusions

For predicting the shaft friction in granular soils, the SCI validation work

(22)(29)

indicates that either the SPT or CPT method can be used with confidence for finegranular soils and the SPT method for all granular type soils using the totalexposed shaft surface area (see sections 4.4.2 and 4.4.3). To predict the ultimatebase resistance on driven steel piles, only the wall cross-sectional area should be

used together with a unit ultimate bearing pressure equal to the CPT value (asverified by Jardine et al(3)). If CPT values are not available then correlations canbe used to deduce an equivalent value from correlations with the SPT.

The offshore pseudo-effective stress method for predicting shaft friction in granularsoils (see Section 4.4.1) was generally not as reliable as the SPT method in theSCI database because of the absence of measurement of N 0 in routine laboratory

soil investigation testing.

4.5 Load resistance in cohesive soils

4.5.1 Prediction of shaft friction from soil tests

For tubular steel piles according to the API Code RP2A(11), the ultimate frictional

resistance on a pile shaft Rs in cohesive soils is estimated using the formula:

Rs = " c u ! s

where " = the pile wall adhesion factor (or soil shear strength modificationfactor) selected for each soil layer,

(Note: " varies with c u and F v’, see Figure 4.7 for tubular piles);

c u = average undrained triaxial test shear strength over the depth interval(layer thickness) being considered

As = exposed area of pile shaft in the soil layer (both external and internal pile surface area unless the tube is plugged).

Guidance on the value of the empirical factor " comes from interpretation of adatabase of over 200 tubular steel pile load tests, ref. Briaud et al(53). It has beenfound that reasonable estimates of ultimate wall friction Rs for steel tubular piles

can be obtained by using the values for " of " = 1.0 for c u = 0 to 24 kpa, and " = 0.5 for c u >72 kpa, with a linear relationship between. These values are


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where c u = average undrained triaxial test shear strength of the clay at the pile base (within a depth of 1.5 D below the tip level); and

! b = full cross sectional area of pile base for plugged tubular or box piles

comprising the pile wall and any soil plug; or= steel wall cross sectional area for unplugged tubular or box piles,and H-piles or sheet piles.

For tubular and box piles, the calculated potential ultimate pile end bearing acrossthe whole cross-section is compared with the internal soil plug skin friction plusthe pile wall end bearing, and the lesser of the two values is taken as the best

prediction.

Resistance from CPT tests

Compressive and tensile resistance:

Unit shaft friction = uc

K" "c

q

N ≡

where in general for overconsolidated clays, N K = 15 to 20, and c u is the undrained triaxial shear strength of the clay.

It has been found in correlation work for clay sites that the conversion factor N Kvaries considerably with the clay type and its preconsolidation history. Hence theCPT formula is not used on its own for pile capacity predictions in clay, being

used only as an ancillary to check the UU undrained triaxial test c u profile for each

clay stratum and thereby to aid judgement of the most representative mean valueinterpretations in arriving at a design profile.

4.6 Load resistance in rock

Where the contribution to load resistance in the pile comes almost entirely from pile tip end bearing in a hard stratum such as a rock layer, the method of geotechnical design will be different to that for soils.

To generate the maximum potential end bearing per pile in rock requires theselection of a cross-section that gives adequate resistance to overall and local

buckling. Pile head deflection will not be the overriding criterion because the pilemovement required to mobilise base resistance in the rock will only be the axialelastic compression of the complete pile length. Prediction of pile ultimate capacityin rock was discussed in Section 2.

Selection of section will also be affected by the pile stiffness required to permit anyhard driving that is necessary to obtain penetration into the buried rock surface and to confirm development of end bearing. However, this must be achieved without damaging the pile and therefore the pile installation planning must include the

prediction of driving stresses using a Wave Equation computer model such asGRLWEAP(27) (see Sections 7.2 and 7.3). The input for end-bearing resistanceshould be realistically assessed from in situ penetration tests and/or uniaxial testson rock cores or reference to driving tests in similar rock. During the site


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specification of a realistic capacity for the load frame to be used for the test piles.Owing to underestimates in the past, it is suggested that at least 3 to 4 times therequired design working load for the pile should be used or a value up to the yield stress of the steel, whichever is the greater.

Interpreted bearing values between 29 MPa and 38 MPa have been measured onsteel test piles in weathered mudstones and sandstones(22), whereas only 2 to 4 MPais given in BS 8004(15).

A geological classification system for chalk materials together with presumed bearing values is given on page 13 of BS 8004, and the text refers to research byHobbs and Healy(55). Later research is contained in CIRIA PR 11 Foundations inChalk (56) The nature of chalk varies significantly across the UK and the designershould recognise the need to classify chalks in a geological and geographicalcontext before extrapolating the results of pile load tests to other sites. However,the hardest chalk is credited in BS 8004 with a bearing value of 1 MPa to

1.5 MPa. It would appear from SCI’s research(22)(29) that at Erith in Kent (Location16) in the Upper Chalk, that some 2 to 3 times this value can be obtained bydriven steel piles in endbearing on the wall area alone. The results at Location 19in Lincolnshire in the Lower Chalk, suggest that where the chalk is intact and

unweathered even higher values, up to at least 15 MPa, are more realistic.

BS 8004 also gives detailed guidance for piles driven into Keuper Marl or the Mercia Mudstone series as it has become known. Data on a series of load tests onH-piles in Keuper Marl(22) indicates that often the shaft friction is best determined by treating all the weathered layers as a granular material and using the APIformula applied to the total surface area of the pile. It is often misleading to treat

the Marl as a ‘cohesive’ material for driven piles due to the presence of fragmentsand layers of remnant rock in the matrix that break up around the penetrating pilethus creating a new granular material. Obviously the prediction method used must be appropriate to the type of pile and to the soil type.

Steel piles to rock should be driven to refusal, with the refusal criterion agreed between the piling specialist subcontractor and the designer such as to limit thedriving stresses to not more than 90% of yield. The driving stress can be reliably

predicted using wave equation programs such as GRLWEAP and checked duringdriving using DPA (see below). A guide in this respect is that piles can be driven

until the blowcount is at about 10 blows per 20 mm or part thereof, or the top of the pile starts to deform plastically, whichever occurs first. In Norway, where

piling into hard rock is an everyday construction problem, they use criteria of 10blows per 1 to 3 mm to define pile “refusal” provided that the blowcount rate hasan increasing tendency.

Where steel sheet piles are used, panel driving should be employed, and stagedriving should be adopted. The first stage objective should be to embed all the

piles and to clutch them all together before any significant hard driving is expected that could damage the clutches. The following stages will then be to redrive inincrements to achieve penetration into the rock.

It is always worthwhile to use dynamic pile driving analysis at the end of drivingsteel piles in rock, due to the high degree of uncertainty in the prediction methodsfor rock resistance. A specialist company can provide a Dynamic Pile Analyser


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(DPA) that uses measured acceleration and stress wave recordings from pileinstruments under a blow of the hammer to interpret the distribution of soilresistance down the pile. Such measurements have been correlated against staticload test records in the SCI validation work for this publication and found to be a

reliable estimate of end resistance in rock strata

(22)

. The use of a DPA also provides direct monitoring of the driving stresses in the pile so that termination of driving can be called when 90% of the yield stress of the steel is approached.

This advance in technology obviates the use of conservative arbitrary rules, suchas are found in BS 6349(6), that were prudent limits at the time to provide against the risk of buckling damage during of steel piles in the days when instrumentationwas not available to the design engineer.

Experience indicates that there is generally no risk of overall buckling of steel pileswhen embedded in soil. Theoretical methods such as ‘Euler Buckling Theory’ arenot relevant, because of the considerable lateral restraint offered by the soil to the

pile shaft (see BS 6349). The only relevant check is that necessary to prevent localbuckling at the pile tip in rock that can be sustained during the driving stage, forexample at the Shaldon Bridge site in Devon(22) where the four trial piles wereextracted and two were found to have toe damage although they were all driven tothe same set. If driving stresses in a pile are controlled to within 90% of the steelyield stress using DPA then such damage should be prevented. Driving stressescan be reliably predicted using a modern Wave Equation pile driveability computeranalysis programme like GRLWEAP(27), provided that the end bearing resistanceforce is correctly input from experienced practitioners. The latter can be ensured if CPT qc values are used, as explained earlier. This should be sufficient to ensureselection of a suitable steel pile section for driving. After load testing, test pilescan be extracted using a vibrating hammer to check the condition of the pile tip.A change of driving procedure or a change of steel section may be necessary forthe working piles depending on the degree of damage observed.

In addition to the high end bearing, dynamic pile load testing shows that in thelowest section of pile the wall friction is also very high, particularly in rock and dense granular materials. This cannot yet be predicted reliably using laboratorytesting or theoretical models for design and therefore test piles are essential.

On-site pile load testing should use a range of cross-sections or possibly different types of steel pile to determine the best and most economic solution for each project.

4.7 Negative shaft friction

Where negative wall friction is likely to occur, due to settlement of the adjacent soil relative to the project piles during their working life, it must be considered inrelation to test loading of the trial pile. Such settlement could originate fromground surface loading adjacent to foundation piles, such as road embankments ornatural consolidation of recent soils or fills, and is a commonly experienced

phenomenon. Obviously such ‘downdrag’ on a pile reduces the available resistanceto structural load and must be allowed for in design.


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4.8 Measures to increase steel pile axial capacity

The maximum potential axial capacity of steel piles is currently rarely used, owingto a combination of factors. These include:

C Designers using conservative resistance prediction methods to specify workingloads and not being prepared to modify the design after the trial pile load tests.

C Designers not selecting the type of pile at the design stage, and thereforeleaving the geotechnical design and selection of pile size and type to afoundations contractor who has not the remit to select the most efficient typeof pile or to redesign the connection to suit.

C The construction industry traditionally not being motivated to be innovativeand to use the most economic and suitable pile type for each site if thedesigner has not covered that alternative.

As laid down in the guidance section of the new ICE Specification for Piling and Embedded Retaining Walls(20), economies in the number and size of steel bearing piles required in any foundation can be effected by using one or other of thefollowing methods:

C Carry out trial pile tests, to ultimate failure or incipient failure by specifyinga head deflection of a minimum of 40 mm in soils, or to full allowable sectionload in rocks, and modifying the number of piles to suit.

C In pile tests, use specialist geotechnical judgement to specify the delay to thestart of pile load application to suit the set-up period appropriate to the soiltype, so that more of the potential capacity has recovered after driving.

C Judge the proportion of resistance attributable to shaft friction and endbearingand then ensure that the steel area in contact with the major contributor ismaximised (for example, weld on wing plates to a skin friction pile or useenlarged shoes for an end bearing pile).

C Use Maintained increment Load Tests (MLT) not Constant Rate of PenetrationTesting (CRP), so that: the load-deflection curve is definitive; the pile reachesan equilibrium between applied load and resistance; and the pile load resistance versus pile head deflection relationship is therefore interpretable.


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5 LATERAL LOAD RESISTANCE

5.1 IntroductionLateral loads on bearing piles range in importance from the major load component in such structures as transmission towers or mooring dolphins, to a relativelyinsignificant force in the foundations of low-rise buildings. The designer must first

judge whether the imposed lateral load on the proposed foundation is significant enough to warrant special analysis.

On buildings for instance, the lateral loading is mainly due to wind pressures. Forlow-rise buildings not exceeding 3 storeys in height, any foundation shearresistance required is normally accommodated by passive earth pressure acting onthe buried pile caps and ground beams of a piled foundation, and on the frictional

sliding resistance beneath the ground floor slab and the foundations. Therefore,the lateral loading on the bearing piles would be insignificant.

Lateral load resistance from vertical bearing piles is particularly dependent on soiltype; in the extreme case of very soft soil, raking piles to an underlying morecompetent soil or rock would be required to provide any significant resistance.

Lateral load resistance from vertical bearing piles also requires significant piledisplacement, of the order of many centimetres, so if this is unacceptable then thedesigner should think of alternative foundation elements to provide it, such asraking piles or embedded sheet pile perimeter walls.

Where the contribution to lateral loading resistance of vertical bearing piles is vitaland an acceptable solution, the designer is recommended to use CIRIA Report 103

Design of laterally loaded piles(13) and the textbooks by Poulos and Davis(23), and Tomlinson(24).

5.2 Methods of analysis

The two most extensively validated methods are the P-Y curve method and elasticcontinuum analysis FE programs. Both are explained in CIRIA Report 103(13).

P-Y curves originate from instrumented lateral load tests carried out on 762 mmOD tubular piles in the USA in the 1960s for offshore design. The models of load resistance were derived from soil resistance distributions required to match thebending stresses measured by the pile shaft strain gauge instrumentation, i.e. curve-fitting to match bending moment diagrams. The P-Y curve method is the only onein which it is possible to allow for significant cyclic loading of piles. This is

useful for the structural design of the pile section, but does not give accuratedisplacements because the single piles had no head restraint. It is explained indetail in the American Petroleum Institute Code RP2A(11) and in computer programslike ‘ALP’ in the OASYS suite(57).

The generic models for P-Y curves for sands and clays are shown in Figures 5.1

and 5.2. They are lateral resistance springs relating load resistance to deflectionfor a discrete layer of soil. The curve is dependent on the diameter or width of the


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Table 5.1 Summary of the output of methods of analysis (from CIRIA

Report 103)

Model Limitations Application Output

Structuralframe

Unrealistic model (thesoil is ignored).

End-bearing pile groups,with a small lateral load

component (say up to 10%

of the vertical load).

Axial load onpiles is the only

reasonable

output.

Winkler

medium

or

p-y analysis

A reasonable model

for single piles.

However,

inappropriate for pile

groups with s/D<8,

because the

continuity of the soil

is not modelled.

Any laterally-loaded single

pile or widely-spaced pile

(s/D>3) group. The

analysis can provide

reasonable predictions for

cyclic loading or account for

the development of plastic

zones if suitable p-y data

are selected.

Depth, slope,

moment and

shear of the pile

at any depth.

Elastic

continuum

A reasonable model

for single piles or pile

groups at working

load. Yield of the

soil cannot be

included exactly.

The limitations

depend on the

mathematics of the

particular computer

solution chosen.

Available programs

are limited toconstant or linearly

increasing soil

modulus with depth.

Single piles or pile groups

under working loads.

Output depends

on the particular

program adopted,

but typically

includes

deflection, slope,

moment, shear

and axial load

distribution for

each pile in the

group, and the

overall stiffness

and/or flexibilitymatrix of the pile

group.

For structures like integral bridges, it may be necessary to carry out a soil/structureinteraction analysis using appropriate stiffnesses to calculate the movement that occurs at the pile head. This could be a total global frame analysis in 2D for atypical frame of a symmetrical structure, or in 3D if the structure is asymmetric.An iterative procedure will be required to obtain a match of displacement and rotation at the pile head if the structure and foundation are modelled separately.This has been common practice in offshore platform design. A ‘P-Y’ or elastic

continuum analysis can be used.

5.3 Assessment of soil properties

There are no clear guidelines for the assessment of soil property values to beadopted for the design of laterally-loaded piles. Many factors influence the actualmobilised values. In particular, the disturbing effect of pile installation is difficult to quantify. Most soils exhibit considerable loss of stiffness under the action of cyclic loading, which is virtually impossible to relate to laboratory test data.Generally, it is desirable to select upper and lower limits to the critical soil

properties, and to check the sensitivity of the design to variation within the chosenrange.


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based on the elastic continuum approach is considered to be one of the most satisfactory methods available at present, provided that the limit ondisplacement is satisfied.

Analysis of the foundation at unfactored working loads enables the designerto assess the significance of the computer predicted deflections and to includethe stiffness matrix of the foundation in the overall design of the structure.

Further information is contained in CIRIA Report 103 Design of laterally loaded piles(13).


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C hydraulic double acting hammer

C diesel hammer

C vibration

C jacking against a reaction.

7.1.1 Drop hammers

The dropping weight, or drop hammer, is the traditional method of pile driving and is still employed. Normally, purpose-made rigs hoist the pile into position, support it during driving and incorporate a guide for the drop hammer (see Figure 7.1).

In guiding the pile, a balance has to be struck between providing suitabledirectional control, and allowing some freedom for slight pile movement within theguides, particularly at the base of the frame. Some twisting or slight lateraldisplacement can occur as a pile is driven. Slight out-of-verticality rarely affects

the pile performance, and slight deviation from a specified pile location can usuallybe tolerated. When driving in boulder clays, it is prudent to allow some overalladditional tolerance in the foundation width to accommodate the eventuality that a

pile may strike a boulder which can cause deflection from its intended position.

Leader mast head

Rear braces

Leader mast foot

Pile rope

Rope head wheels

Hammer cage

Drop hammer

Pile helmet

Inner leader mast

Pile

Leader foot bottom

Hammer hydraulic ram

Flexible hydraulic pipe

Leader foot hydraulic ram

Lower raking hydraulic ram

Upper rakinghydraulic ram

Two hydraulicwinches

Two stage hydraulic ram

Figure 7.1 A steel pile driving rig

Drop hammers should be used with a ram mass of between 0.5 to 2 times the pileweight, with the falling height usually being in the range of 200 mm to 2 m.


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to driving piles in clay where the majority of driving resistance is friction on the pile shaft.

Hydraulic hammers are more efficient and quieter in operation than other types,

and are increasingly used in place of simple drop hammers and diesel hammers inmany applications. They are compact and adaptable and may be used on a widevariety of bearing piles, including raking piles, and with only slight modification,may be used underwater.

There is a wide range of hydraulic hammers available worldwide produced byseveral manufacturers. This competition and their popularity has encouraged theirdevelopment in both technology and size to tackle the largest sizes of pile and withhighly sophisticated instrumentation to measure energy output reliably.

7.1.4 Vibratory methods of pile driving

Vibratory hammers are usually electrically powered (but may be hydraulically powered), and consist of contra-rotating eccentric masses within a housing attached to the pile head. The majority of pile vibrators run at low frequencies, typically20 to 40 Hz. At these frequencies, neither the exposed length of pile nor the soilwill be in resonance. Sound propagation is low and in cohesionless soils good rates of progress can be realised. During the driving progress, the granular soilimmediately adjacent to the pile is effectively fluidised, and friction on the shaft is considerably reduced.

In cohesive soils, fluidization will not occur and vibratory pile driving methods arenot generally as effective. Vibratory hammers are often used as the initial drivebut the final drive uses an impact hammer.

The noise and vibration propagation for vibratory type hammers need to be related to the types of soil at the site in order to minimise the environmental impact.

7.1.5 Resonance pile driving

Variable frequency vibrators can be used to good effect in some soils and can be useful in environmentally sensitive areas provided that the equipment is suitablefor the soil conditions. If the frequency of vibration is increased up to perhaps 100Hz, the pile will resonate longitudinally, and penetration rates can approach 20metres per minute in loose to moderately dense granular soils. At thesefrequencies, non-cohesive soils are fluidized to the point where the frictionalresistance on the pile shaft is reduced to close to zero and more driving energy isdelivered to the pile toe.

This method of pile installation is potentially very effective but needs thoroughinvestigation by the user and the manufacturer to relate hammer mass and frequency reliably to the type of soil.

7.1.6 Jacking methods of pile installation

Lengths of pile, either in short units or in continuous lengths, may be forced intothe ground by jacking (usually hydraulically) against a reaction. Jacking methodsare exceptionally quiet and vibration-free in use, and by monitoring the pressurein the hydraulic system a good understanding of soil resistance can be obtained


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0 is the assumed efficiency of the hammer (allowing for the energy losson impact)

W is the weight of the hammerh is the drop height

s is the permanent ‘set’ of the pilec is the elastic or recoverable movement of the pile.

The formula 7.1 is widely used in the USA adopting a value of 0.8 to 1 for 0 and 2.5 mm for c, giving the so-called Engineering News formula(77). In Europe, both0 and c are chosen with regard to the type of hammer; the type of material used in the cushion at the head of the pile and the physical properties of the pile.

Probably the best known variant of the formula is that due to Hiley (28) where theoverall hammer system efficiency (including hammer, anvil, capblock, cushion) isgiven by:

7.2η =

+

+

k W e W

W W

( )2

p p

where k is the output efficiency of the hammer (ratio of power delivered at the cushion to the rated hammer power);

W p is the weight of the pile;e is the coefficient of restitution between the hammer and the capblock

cushion, or top of pile if there is no cushion.

The recoverable movement c is taken as c = cc + c p + cg where the cushioncompression, cc = R t c/( AE )c, where t c is the thickness and ( AE )c the cross sectional

rigidity of the cushion, the elastic shortening of the pile (considered as a column),c p = Rl /( AE ) p and the recoverable movement of the ground cg which may be takenas 0.5% of the pile diameter.

Tables 7.1 and 7.2 show commonly adopted values for the quantities k , e and E depending on hammer type and cushion material.

The Hiley formula can be presented in the form of a nomogram as shown inFigure 7.3. The Figure shows a chain dotted path of an example to demonstrateits use.

The particular example illustrated is a 20 m long, 150 kg/m, steel bearing pile

driven to a final set of 2.5 mm per blow with a 4 tonne ram single acting hammer,the drop height being 1.0 m. The ultimate driving resistance R of 1820 kN canthen be read off directly. Thus, applying a factor of safety, in this case 2.0, themaximum working load would be 910 kN. However, this driving resistance is not often equal to the static load resistance of the pile owing to the changes in soilresistance which occur with time in soils.


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7.3.2 Wave equation methods

A more rigorous investigation of the driving behaviour of a pile may be achieved by means of ‘wave equation’ dynamic analysis of the pile-soil system. The inertialeffects of the soil around the pile and the viscous nature of the soil may both be

taken into account by appropriate numerical techniques, such as the finite element method (see Smith and Chow(79)). A common simplification is to treat the soil asa massless medium providing friction resistance alone, while the pile is modelled as a discrete assembly of mass elements, interconnected by springs, see Figure 7.4.

a) Actual system b) Model

Air/steam

Diesel

Ram

AnvilCapblockHelmet

Pile

Cushion

Soil

Ru

Velocity Displacement

q

S t a t i c

r e s i s t a n c e

J

c) Soil model

D y n a m i c

r e s i s t a n c e

Figure 7.4 Wave Equation Model for pile driveability prediction

At the design stage the main objective of dynamic analysis of pile driving is toassess the ‘driveability’ of a pile in given soil conditions and to determine a

pile+hammer combination that can satisfactorily achieve the required design pile penetration for the predicted static soil resistance with acceptable driving stresses.This is commonly accomplished using one dimensional wave equation programs:

probably the most widely used program is GRLWEAP. The program wasoriginally developed in the USA by Goble and Rausche(80) between 1976 and 1988

and has a comprehensive user manual.


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7.4 Pile load testing

It should be borne in mind that the prediction methods for axial pile load capacityfrom soil tests as described in Sections 4.4 and 4.5, are primarily a means of estimation for the conceptual design stage of the foundation. Reference to the SCIdatabase of results on steel piles (ref. SCI Technical Report 242 (22)) and Jardineet al(3) shows that although these methods can give an acceptable mean and standard deviation in reliability terms, there is always a scatter about such a mean and thechance of an erratic result on any site due to the variability of soils. This, coupled with the inevitable problem of determining an appropriate measure of ‘soilstrength’ from laboratory soil tests, means that wherever possible the opportunityshould be taken to conduct a pile load test as the only assured method of load resistance determination. Once a trial pile test has been performed and the

pilehead load/resistance curve obtained, the wall friction may be separated from theend-bearing by methods such as CEMSOLVE(81)(82)(83). The designer can thencalibrate the results against the soil profile and extrapolate across the site using the

variations in the soil layering found in the site investigation to predict potentialchanges in pile capacity.

It is desirable to carry out test loading to failure wherever possible, in order todetermine the ultimate pile load capacity and to obtain the full pilehead load/deflection relationship. Generally, driven steel piles can be tested to the

ultimate load without affecting subsequent load carrying capacity, because of themanner in which soil resistance is generated (see explanation in Section 2.5). A

possible exception is where piles are driven to hard rock, where the ultimate load may be governed by local buckling of the steel section as a result of high stressesat the tip, rather than downward movement into the rock; any pile damage due tooverload may reduce subsequent load carrying capacity.

In some cases the designer only requires test piles to be ‘proof loaded’, and herethe applied load may be specified to be between 1.3 to 2 times the required ‘working’ load; a frequently used factor being 1.5. In ‘proof loading’ it is usuallyrequired that the pile shall not have failed at the specified proof load, and that the

pile head settlement shall not exceed the specified serviceability limit. However,as discussed in section 2 and shown in Figure 2.1 there are benefits to thedesigner in specifying load testing up to 2 times the estimated design working load and in achieving a pile head displacement of 40 mm whenever possible, in orderto define the ‘ultimate capacity’. The proof loading approach predetermines thenumber of piles without permitting the economies that can be obtained from static

load tests to failure.

Static load testing is expensive and time consuming as compared to dynamictesting. In addition, if the estimate of static load resistance from soil and rock samples is too low, it is rarely possible to increase the load range sufficientlywithin a kentledge or anchor pile test set-up to reach the ultimate pile capacity (seeFigures 7.6 and 7.7). If dynamic pile testing is used there are no suchimpediments, and it is therefore potentially a far superior method. Now that theaccuracy and reliability of dynamic pile testing has been established, and it hasbecome accepted practice (see the ICE Specification for Piling and Embedded

Retaining Walls(20)), it could rapidly become the norm. The CAPWAP pile drivinganalysis also provides another motivation, which is that pile stresses can be checked


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Tie-bars

Isolated datum beam formeasuring settlement

Anchor pileseach side

Loading jack

Loadcell

Secondary loadingbeams

Pile under test

Main loading beams

Figure 7.7 Test load arrangement using anchor piles

CRP, the constant rate of penetration test

The second method is the constant rate of penetration (CRP) test . The loadingarrangement of the apparatus is the same as for the maintained load test, but theload is increased continuously at a rate such that the settlement of the pile head occurs at a constant rate per minute.

The constant rate of penetration test (CRP) has been demonstrated to be unreliable

and uninterpretable in respect of deriving and understanding ultimate pilecapacity (ref. Fleming(81)). For static pile load tests, and ULS design procedures,the CRP type of test should be discontinued in favour of a maintained increment load test (MLT) that can give a reliable indication of the ultimate load resistance.In addition, the time allowed for each stage of load application should be increased in line with the recommendations of England and Fleming(84) to permit development of the equilibrium resistance to the applied load.

Comment on testing procedures

Excessive conservatism has been found in current practice and in the currently used specifications for load testing piles, which has been compounded by unrealistic

design assumptions on the soil parameters that are used in pile resistance predictionmethods. Consequently, designers are unable to interpret the ultimate pile capacityfrom their load test results, and the whole basis of the new limit state design

procedures is denied. It is hoped that the guidance given herein will help correct these errors and thereby permit more economic pile design.

Testing steel piles nearer to their ultimate capacity instead of to ‘nominal’ or tooverconservatively assessed design ‘working loads’ will improve knowledge of their behaviour and permit improvements to the currently restrictive design rules.


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By waiting a period of time and remounting the hammer on the pile, the ‘set-upeffect’ or change in soil resistance with time can be determined from restrikeblows.

Obviously the confidence that the designer will have in the static capacity‘prediction’ results from dynamic analysis will be greatly enhanced if a correlationcan first be carried out against a static capacity test on a trial pile at the site.However, the SCI have obtained good correlation between static and dynamiccapacities for granular soils and rocks in their database (ref. SCI Technical Reports242(22) and 243(29)) and this endorses the use of dynamic test methods for thoseconditions.

On clay sites, dynamic testing has to be carried out with care to understand anyset-up effects that may occur after driving the steel piles, and thereby to avoid interpretation of too pessimistic a value for the ultimate load resistance.

Equally, there are often cases of a reduction of capacity with time, particularlywhen driving piles into shales and mudstone bedrocks and when piles are veryclose together in a group. Hence it is always of value to carry out restrike testsas part of the standard procedure when dynamic testing is available, to avoid reliance on unnecessarily high factors of safety as factors for ‘ignorance’.

The ability of CAPWAP to separate shaft friction from endbearing resistance is avery useful tool and is particularly useful in predominantly endbearing piles.

Pile stress analysis using a Pile Driving Analyser and pile instrumentation can bean aid to onsite control, particularly when hard driving is required to establish a

high end bearing resistance and minimise pile tip damage. On such sites it is oftenbeneficial to extract the test piles to check for such damage. This will permit a moreconfident basis for the ‘set’ to be used as a control during driving of the working

piles.

7.5 Steel pile installation tolerances

It is not possible to install piles to fine tolerances of a level or position or of horizontal or vertical alignment. The achievable tolerances are strongly related tofactors such as the accuracy in setting up the piling equipment; the accuracy or‘repeatability’ of the measurement system; the fixity in machine parts; any presence

of obstructions in the ground and any variations in the properties of the soilespecially near the point of entry of the pile into the ground surface; the inclinationof the strata; and operator error. The pile design should allow for bending stressescaused by a specified inaccuracy in the installed position of a pile that has beenagreed with the installation contractor. The order of magnitude for toleranceswhich can normally and reasonably be achieved are quoted in certain specialist

publications for example the ICE Specification for Piling and Embedded RetainingWalls(20).

Typical tolerances quoted for bearing piles generally include:

C a positional tolerance of 75 mm and

C a maximum of 1 in 75 on axial line for vertical piles.


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7.6.1 Noise from piling operations

Pile driving is an inherently noisy operation. Noise levels of 85 decibels within10 m of the piling plant are quite common. Typical data on noise levels produced by piling operations have been published in CIRIA Report 64 Noise from

construction and demolition sites - measured levels and their prediction(91). Theseare discussed and interpreted in CIRIA Report PG9 Noise and vibrations from

piling operations(92). Environmental restrictions can be imposed in the Conditionsof Contract for a project.

Investigations into the sources of the noise have shown that a large proportion of it arises from secondary effects, rebound of the hammer, rope slap, engine noise,etc. Improved design of the components of a piling rig can considerably reducethe high-frequency content of the noise emitted. To dampen the noise sufficientlyto be acceptable in urban situations, it may be necessary to enclose the hammer orthe guide rails in an ‘acoustic chamber’. The use of such devices usually results

in some reduction in the efficiency of the pile hammer and can create difficultiesin handling and pitching piles. Alternatives to drop and diesel hammer types suchas hydraulic hammers with a ‘skirt’ can reduce the noise because the point of impact of the ram to the top of the pile is enclosed.

Driving steel sheet piling is often exceedingly noisy since the driving cap usuallyinvolves steel to steel contact. In areas where severe restrictions are placed onnoise levels, pile driving vibrators or the ‘Taywood Pilemaster’ hydraulic piledriver may be adopted. Such machines emit a different frequency and lower levelof noise that can be acceptable, but they involve the use of an auxiliary power unit which may itself emit a high level of noise and must be enclosed by an appropriatemeans.

7.6.2 Ground vibrations caused by piling

It is widely recognised that noise and vibration, although related, are not amenableto similar curative treatment. In the main, noise from site is airborne and consequently the prediction of noise levels is relatively straightforward, given thenoise characteristics and mode of use of the equipment. On the other hand, thetransmission of vibration is largely determined by site soil conditions and the

particular nature of the structures involved. General guidance can be derived fromthe study of case histories of similar situations. Useful references on the subject of ground vibrations are provided by CIRIA Technical Note 142 Ground-bornevibrations arising from piling(93), the publication Dynamic ground movements -man-made vibrations in ground movements and their effects on structures(94) and byBRE Digest No. 403 Damage to structures from ground-borne vibration(95) and thereferences given in Section 7.6.1.

Prediction of peak-to-peak acceleration or velocity in real situations is not straightforward. Firstly, the energy transfer to soil is poorly understood and attenuation of high-frequency components is rapid. Secondly, the response of various forms of construction in adjacent inhabited buildings to ground vibrationsis difficult to predict, and some structural details e.g. floor spans which resonate,may lead to a magnification of the effect. The most widely accepted of thesecriteria are based on the peak particle velocity or the energy intensity of the

vibrations induced in the soil adjacent to the foundations of a building. Empiricalguidelines have been drawn up using these criteria to define various levels of


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‘damage’. One of the most popular of these is included in the German Standard DIN 4150(96), the recommendations of which are listed in Table 7.3.

Table 7.3 Maximum allowable peak particle velocity (from DIN 4150)

Class Description Max velocity

mm/s

1 Ruins and buildings of historical value 2

2 Buildings with existing defects 5

3 Undamaged buildings in technically good

condition

10

4 Strong buildings, and industrial buildings 10-40

These recommendations have not been drawn up specifically for ground vibrations

induced by piling, and it is considered that they are overly stringent for that purpose. For structures which are not of great prestige or historical value it isconsidered that the limits in Table 7.3 could well be doubled without noticeableeffect.

When considering reasonable limits for ground vibrations, the ambient background level of vibration should be assessed. In built-up areas, heavy traffic can causesurprisingly high intensities of vibration and peak-to-peak velocities exceeding3 mm/s have been recorded at a distance of 10 m from a road.

The use of empirical limits on velocity or accelerations in specifications and contracts necessitates the use of field instrumentation to observe the actual induced vibrations. Several levels of recording are possible. The simplest is manualrecording of peak-to-peak signals and the most complex is a full record of theground vibrations to enable a frequency analysis to be carried out.

In general, human perception of vibrations occurs at levels which are low incomparison with the thresholds of risk for structural damage. BS 6472(90) sets out Tables for vibrations in various different types of accommodation for vibrations inthe range 1 Hz to 80 Hz. The vast majority of piling operations currently in usegive rise to vibrational energy within this range.

Various expedients may be adopted to reduce the intensity of ground vibrations

caused by piling.

Steel piles have low displacement and cause less ground disturbance than fulldisplacement piles but further reduction of vibration can be obtained by preboring.Since steel piling takes very little time to install and is an appropriate constructionmethod for most soil types, it has advantages to the contractor.

Public irritation and objections to noise and vibration from piling installation canbe minimised and their cooperation gained by prior notice and careful advice and explanation by the contractor.


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9.2 Corrosion in soil

Corrosion in natural soils is electrochemical in nature and unless the soils arestrongly acidic, i.e. pH<4, the corrosion of steel depends upon the simultaneous

presence of oxygen and water.

In undisturbed natural soils, oxygen concentrations are very low at a very short distance below the ground surface. Steel corrosion rates are therefore very low inthese circumstances, and are not related to the nature of the soil, its compositionor its properties.

The best evidence available is that given by Romanoff in his first report on steel piles(100) and supported by his later report (101) on further investigations. In themajority of cases reported by him the piles were not painted before installation.The following is quoted from Romanoff’s summary in his first report :

“The data indicate that the type and amount of corrosion observed on the steel pilesdriven into undisturbed natural soil, regardless of the soil characteristics and properties, is not sufficient to significantly affect the strength or useful life of pilesas load-bearing structures.”

“.....Undisturbed soils are so deficient in oxygen at levels a few feet below theground or below the water table zone, that steel piles are not appreciably affected by corrosion, regardless of the soil types or the soil properties. Properties of soilssuch as type, drainage, resistivity, pH or chemical composition are of no practicalvalue in determining the corrosiveness of soil on steel piles driven underground.”

Ohsaki(102) evaluated the performance of piles driven into natural soil deposits at tensites in Japan. The sites were spread widely over the whole country and selected where soil conditions were likely to be corrosive. The report concluded that theaverage corrosion rate was approximately 0.005 mm/year/side and that themaximum corrosion rate measured was 0.015 mm/year/side.

British Steel plc has also examined extracted piles from sites in the United Kingdom ranging from beaches, river beds and harbours to inland sites,representing a wide range of soil types and conditions. The results obtained support the findings of Romanoff and Ohsaki.

Guidance on corrosion allowances for piles in natural soils is given in Section 4.4.4

of BS 8002 where the maximum corrosion rate of 0.015 mm/year/side is advised and no other protection is required. This is within the range quoted in Section10.3.5 of BS 8004(15).

9.3 Atmospheric corrosion

The rate of atmospheric corrosion can be taken to be on average of 0.035mm/year/side, as recommended in BS 8002. In areas of high industrial pollutionhigher rates may be encountered, as given in BS 8004, but the incidence of thesein the British Isles is diminishing as industry complies increasingly with the EClegislation to control pollution emissions to the atmosphere.


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9.4 Corrosion below water

Design allowances for the corrosion of steel piles wholly immersed in water arecovered in BS 6349(6), BS 8002 and BS 8004. A mean corrosion rate of 0.035 mm/year/side as advised in BS 8002 can be used for permanent immersionin sea-water to calculate sacrificial allowances. Corrosion rates in fresh water aregenerally lower, and guidance is given in BS 8004.

9.4.1 Low-water zone corrosion

This narrow zone occurs at the bottom of the tidal range where a lack of marinegrowth is often observed and higher corrosion rates are often experienced,normally about 0.075 mm/year/side. Occasionally, corrosion rates which aresignificantly higher than this value arise because of specific local conditions, and it is recommended that periodic inspection of this zone is undertaken.Investigations into this form of corrosion are reported in Accelerated low water

corrosion of steel sheet pile marine walls

(103)

.

9.4.2 Tidal zone corrosion

Tidal zones tend to accumulate growths of barnacles and seaweeds which afford protection to the steel, principally by limiting the supply of oxygen to the surface.Examination of piles in UK harbours indicates a mean corrosion rate of 0.035 mm/year/side, similar to that observed in the fully immersed zone.

9.4.3 Splash and marine atmospheric zones

These are above the tidal range, the former being subject to wave action and salt spray and the latter mainly to airborne chlorides. Splash zone corrosion dependson the degree of shelter from wave action and thus is variable. Examination of structures in UK harbours produced a mean corrosion rate of 0.075 mm/year/sidein the splash zone, though in extreme cases of exposure to full wave and stormconditions values up to 0.125 mm/year/side are possible. Upper range values arequoted in BS 6349(6) for various exposures.

The boundary between the splash and atmospheric zones is not well defined;corrosion rates diminish rapidly with distance above peak wave height and themean atmospheric corrosion rate of 0.035 mm/year/side can be used for this zone.

9.5 Methods of increasing effective lifeThere are five main options to increase the effective life of a designed steel pilesection. These are all covered in BS 8002(5), BS 6349(6) and the British Steel Piling

Handbook . The action to be taken will depend on individual circumstances and cost-benefit analysis. The options are:

C Use a heavier section than that structurally required.

C Substitute a pile with a higher yield quality of steel.

C Apply a protective coating.

C Use concrete encasement where practicable.


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10. CORNFIELD, G.M.Steel Bearing Piles, Fourth EditionThe Steel Construction Institute, 1989

11. AMERICAN PETROLEUM INSTITUTEAPI Recommended practice 2A-LRFD (RP2A-LRFD), 1st EditionRecommended practice for planning, designing and constructing fixed offshore platforms - load and resistance factor designAPI, 1993

12. INTERNATIONAL ORGANIZATION FOR STANDARDISATION(ISO)13819-2: Petroleum and natural gas industries: offshore structuresPart 2: Fixed steel structuresISO, 1995

13. ELSON, W.K.Design of laterally-loaded pilesCIRIA Report 103Construction Industry Research and Information Association, 1984

14. PADFIELD, C.J. and MAIR, R.J.Design of retaining walls embedded in stiff clayCIRIA Report 104Construction Industry Research and Information Association, 1984

15. BRITISH STANDARDS INSTITUTION

BS 8004: Code of practice for foundationsBSI, 1984

16. BRITISH STANDARDS INSTITUTIONBS 8081: Code of practice for ground anchorsBSI, 1994

17. BRITISH STANDARDS INSTITUTIONBS 8006: Code of practice for strengthened/reinforced soils and otherfillsBSI, 1995

18. EUROPEAN COMMITTEE FOR STANDARDISATION (CEN)Draft prENV 1993-5Eurocode 3: Design of steel structuresPart 5: PilingCEN, 1996

19. BRITISH STANDARDS INSTITUTIONBS 449: Specification for the use of structural steel in buildingBSI


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74. Euripides Pile Test ProgramTubular steel pile load tests in sand, 1994-1996Joint Venture Project ReportsFugro-McClelland Engineers B.V. and Geodia S.A.

75. AKBARI, N.A. and MURE, A.Investigation of methods of prediction and measurement of thebehaviour of three types of driven piles at Isle of Grain, UK.Paper 21 Piling practice and worldwide trends, edited by M. J. SandsInstitution of Civil Engineers, Thomas Telford, 1992

76. WHITAKER, T.The design of piled foundations, 2nd EditionPergamon Press, Oxford

77. FLEMING, W.G.K., WELTMAN, A.J., RANDOLPH, M.F. and

ELSON, W.K.Piling Engineering. 2nd EditionBlackie A and P, 1994

78. FLAATE, K.An investigation of the validity of three pile driving formula incohesionless materialNGI Publication No. 56, pp 11-22Norwegian Geotechnical Institute, Oslo, Norway, 1964

79. SMITH, I.M. and CHOW, Y.K.

Three dimensional analysis of pile driveabilityProc. 2nd Int. Conf. On Numerical Methods in Offshore Piling, Austin, pp 1-10, 1982

80. GOBLE, G.G. and RAUSCHE, F.Wave equation analysis of pile driving - WEAP ProgramVol. 1 - Background, Vol. 2 - User’s Manual , Vol. 3 - Programdocumentation, Report No. FHWA - IP - 76-14.1, 2, 3,National Technical Information Service, Springfield, Virginia 22161,July 1976

81. FLEMING, W.G.K.

A new method for single pile settlement prediction and analysisGeotechnique 42, No. 3, 411-425, 1992

82. ENGLAND, M.Pile settlement behaviour: An accurate modelProc. Conference on application of stress-wave theory to piles,A.A. Balkema Publishers, Rotterdam 1992

83. ENGLAND, M.Paper 3-14: The role of driven pile instrumentationDeep Foundations Institute Conference, 1994, Belgium

Deep Foundations Institute, New Jersey 07632, USA


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94. SKIPP, B. O.Dynamic ground movements - man-made vibrations in ground movements and their effects on structuresBlackie, Glasgow and London, pp 381-434

95. BUILDING RESEARCH ESTABLISHMENTDamage to structures from ground-borne vibrationBRE Digest No 403, 1995

96. DIN (DEUTSCHES INSTITUT FÜR NORMUNG)DIN 4150: Part 3: Structural vibration in buildings: effects on structuresDIN, 1986 (draft 1997 not yet translated into English)

97. “Sheet piles stand the test of time”Ground Engineering (the magazine of The British Geotechnical Society),Volume 40, Number 4, p4, May 1997

98. BRITISH STEEL SECTIONS, PLATES & COMMERCIAL STEELSThe corrosion and protection of steel piling in temperate climatesBritish Steel Publication P115, February 1994

99. BRITISH STEEL SECTIONS, PLATES & COMMERCIAL STEELSThe prevention of corrosion on structural steelwork British Steel Brochure reference SPCS 501 3 5/96, May 1996

100. ROMANOFF, M.Underground corrosion

National Bureau of Standards, circular no. 579: 1957US Dept. of Commerce, Washington DC

101. ROMANOFF, M.Corrosion of steel piling in soilNational Bureau of Standards, monograph no. 58: 1962US Dept. of Commerce, Washington DC

102. OHSAKI, Y.Corrosion of steel piles driven in soil depositsSoils and Foundations Journal, Vol. 22, No. 3., Sept. 1982Japanese Society of Soil Mechanics and Foundation Engineering

103. ROWBOTTOM, D.Accelerated low water corrosion of steel sheet pile marine wallsBritish Steel Piling Technical, Scunthorpe, 1996

104. HIGHWAYS AGENCYQuote from Lawrie Haynes, Director, 1996

105. BRITISH STANDARDS INSTITUTIONBS 7361: Cathodic Protection, Part 1: Code of practice for land and marine applications

BSI, 1991


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106. BRITISH STANDARDS INSTITUTIONBS 1377: 1990 Methods of tests for soils for civil engineering purposesBSI, 1990


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APPENDIX A CONTACTS

British Steel, Sections, Plates & Commercial Steels

Piling Technical ServicesPO Box1Brigg Road ScunthorpeNorth LincolnshireDN16 1BP.Tel: 01724 404040, Fax: 01724 282603

Federation of Piling Specialists (FPS)

39 Upper Elmers End Road Beckenham

Kent BR3 3QYTel: 0181 663 0947, Fax: 0181 663 0949

Technical European Sheet Piling Association (TESPA)

PO Box 8413D-4000 Dusseldorf 1and19 Avenue de la LibertéL-2930 Luxembourg

Additional contact information for steel piling contractors and suppliers is given inthe Steel Construction Yearbook, available from the SCI.


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