Recommendations on Piling (EA Pfähle) E-Book

• Herausgeber: Wiley-VCH
• Kategorie: Wissenschaft und neue Technologien
• Serie: Ernst & Sohn Series on Geotechnical Engineering
• Sprache: Englisch

Seitenzahl: 621

Veröffentlichungsjahr: 2013

Beschreibung

This handbook provides a complete and detailed overview of piling systems and their application. The design and construction of piled foundations is based on Eurocode 7 and DIN 1054 edition 2010 as well as the European construction codes DIN EN 1536 (Bored piles), DIN EN 12699 (Displacement piles) and DIN EN 14199 (Micropiles). These recommendations also deal with - categorisation of piling systems, - actions on piles from structural loading, negative skin friction and side pressure, - pile resistances from static and dynamic pile test loading as well as extensive tables with the pile load-bearing capacity of nearly all piling systems based on values from practical experience, - pile groups, - performance of static and dynamic test loading and integrity tests, - load-bearing behaviour and verifications for piles under cyclical, dynamic and impact actions - quality assurance for construction. An appendix with numerous calculation examples completes the work. As part of the approval procedure for offshore wind energy structures, the Federal Office for Shipping and Hydrography (BSH) demands verifications according to the new Chapter 13 ("Load-bearing behaviour and verifications for piles under cyclical, dynamical and impact actions") of the EA Pfähle (the recommendations of the Piling working group - 2nd edition), which deals with external pile resistance for the foundations of offshore wind energy structures and the types of verifications to be provided under cyclical actions. The publication of the EA-Pfähle recommendations by the Piling working group of the German Society for Geotechnics (DGGT), which works with the same members as the piling standards committee NA 00-05-07, is intended to provide assistance for engineers active in the design, calculation and construction of piled foundations. The recommendations can thus be considered as rules of the technology and as a supplement to the available codes and standards.

Leseprobe

Inhaltsverzeichnis

Members of the AK 2.1 Piling Committee of the German Geotechnical Society

Preface of the English Version of the Recommendations of the Piling Committee of the German Geotechnical Society

Preface of the 2nd German edition

1 Introduction to the Recommendations and their Application Principles

1.1 National and International Regulations for Piling Works

1.2 Types of Analysis and Limit States using the Partial Safety Factor Approach

1.3 Planning and Testing Pile Foundations

2 Pile Systems

2.1 Overview and Classification into Pile Systems

2.2 Pile Construction

2.3 Foundation elements similar to piles

3 Pile Foundation Design and Analysis Principles

3.1 Pile Foundation Systems

3.2 Geotechnical Investigations for Pile Foundations

3.3 Classification of Soils for Pile Foundations

3.4 Pile Systems for the Execution of Excavations and for Retaining Structures

3.5 Piles for the Stabilisation of Slopes

3.6 Use of sacrificial Linings

4 Actions and Effects

4.1 Introduction

4.2 Pile Foundation Loads Imposed by the Structure

4.3 Installation Effects on Piles

4.4 Negative Skin Friction

4.5 Lateral Pressure

4.6 Additional Effects on Raking Piles Resulting from Ground Deformations

4.7 Foundation Piles in Slopes and at Retaining Structures

5 Bearing Capacity and Resistances of Single Piles

5.1 General

5.2 Determining Pile Resistances from Static Pile Load Tests

5.3 Determining Pile Resistances from Dynamic Pile Load Tests

5.4 Axial Pile Resistances Based on Empirical Data

5.5 Bored Piles with Enlarged Bases

5.6 Additional Methods Using the EC 7-1 and EC 7-2 Handbooks

5.7 Pile Resistances for Grouted Shafts and Bases

5.8 Resistances of Piles Under Lateral Loads

5.9 Pile Resistances Under Dynamic Actions

5.10 Internal Pile Capacity

5.11 Numerical Analyses of the Capacity of Single Piles

6 Stability Analyses

6.1 Introduction

6.2 Limit State Equations

6.3 Bearing Capacity Analysis

6.4 Serviceability Analysies

6.5 Pile Groups and Grillages

6.6 Piled Raft Foundations

7 Grillage Analysis

7.1 Analysis Models and Procedures

7.2 Non-linear Pile Bearing Behaviour in Grillage Analysis

8 Analysis and Verification of Pile Groups

8.1 Actions and Effects

8.2 Bearing Capacity and Resistances of Pile Groups

8.3 Bearing Capacity Analyses

8.4 Serviceability Analyses

8.5 Higher Accuracy Pile Group Analyses

9 Static Pile Load Tests

9.1 Introduction

9.2 Static Axial Pile Load Tests

9.3 Static Lateral Load Test

9.4 Static Axial Load Tests on Micropiles (Composite Piles)

10 Dynamic pile load tests

10.1 Introduction

10.2 Range of Application and General Conditions

10.3 Theoretical Principles

10.4 Description of Testing Methods, Test Planning and Execution

10.5 Evaluation and Interpretation of Dynamic Load Tests

10.6 Calibrating Dynamic Pile Load Tests

10.7 Qualifications of Testing Institutes and Personnel

10.8 Documentation and Reporting

10.9 Testing Driving Rig Suitability

11 Quality Assurance during Pile Execution

11.1 Introduction

11.2 Bored Piles

11.3 Displacement Piles

11.4 Grouted Micropiles (Composite Piles)

12 Pile Integrity Testing

12.1 Purpose and Procedures

12.2 Low Strain Integrity Tests

12.3 Ultrasonic Integrity Testing

12.4 Testing Piles by Core Drilling

12.5 Other Specific Testing Methods

13 Bearing Capacity and Analyses of Piles under Cyclic, Dynamic and Impact Actions

13.1 Introduction

13.2 Cyclic, Dynamic and Impact Actions

13.3 Supplementary Geotechnical Investigations

13.4 Bearing Behaviour and Resistances under Cyclic Loads

13.5 Bearing Behaviour and Resistances under Dynamic Loads

13.6 Bearing Behaviour and Resistances under Impact Loads

13.7 Stability Analyses of Cyclic, Axially Loaded Piles

13.8 Stability Analyses of Cyclical, Laterally Loaded Piles

13.9 Stability Analyses of Dynamic or Impact-loaded Piles

Annex A Terms, Partial Safety Factors and Principles for Analysis

A1 Definitions and notations

A2 Partial safety factors γF and γE for actions and effects from EC 7-1Handbook [44], Table A 2.1

A3 Partial Safety Factors for Geotechnical Parameters and Resistances from EC 7-1 Handbook [44], Tables A 2.2 and A 2.3

A4 Correlation Factors ξi for Determining the Characteristic Pile Resistances for the Ultimate Limit State Acquired from Tested or Measured Data of Static and Dynamic Pile Tests acc. to the EC 7-1Handbook

A5 Procedure for Determining the Resistance of Piles Against Buckling Failure in Soil Strata with Low Lateral Support (informative)

A6 Bonding Stress in Grouted Displacement Piles (informative)

Annex B Example Calculations for Pile Resistance Analysis and Verifications

B1 Determining the Axial Pile Resistances from Static Pile Load Tests, and Ultimate and Serviceability Limit State Analyses

B2 Characteristic Axial Pile Resistances from Dynamic Load Tests

B3 Determining the Characteristic Axial Pile Resistances from Empirical Data for a Bored Pile

B4 Determining the Characteristic Axial Pile Resistances from Empirical Data for a Prefabricated Driven Pile

B5 Determining the Characteristic Axial Pile Resistances from Empirical Data for a Fundex Pile

B6 Principle of the Evaluation of a Static Pile Load Test Using a Prefabricated Driven Pile shown on an Example and Comparison with Empirical Data after 5.4.4.2

B7 Preliminary Design and Analysis of the Ultimate Limit State of Franki Piles Based on Empirical Data and Comparisontoa Pile Load Test Result

B8 Negative Skin Friction for a Displacement Pile as a Result of Fill

B9 Determining the Effect on a Laterally Loaded Pile (Perpendicular to the Pile Axis) and Analysis of Structural Failure

B10 Laterally Loaded Piles

B11 Pillar Foundation on 9 Piles–Ultimate and Serviceability Limit State Analyses Taking the Group Effect into Consideration

B12 Tension Pile Group Analyses in the Ultimate Limit State

B13 Laterally Loaded Pile Groups: Determining the Distribution of Horizontal Subgrade Moduli

Annex C Examples of Dynamic Pile Load Testing and Integrity Testing

C1 Dynamic Pile Load Test Evaluation: Example using the Direct Method

C2 Dynamic Pile Load Test Evaluation Example Using the Extended Method with Complete Modelling

C3 Rapid Load Tests Evaluation Example Using the Unloading Point Method

C4 Low Strain Integrity Test Case Studies

C5 Integrity Tests during Driving and/or High Strain Integrity Tests

C6 Example: Ultrasonic Integrity Testing

Annex D Analysis Methods and Examples for Cyclically Loaded Piles (Informative)

D1 Guidance notes

D2 Piles Subjected to Cyclic Axial Loads

D3 Piles Subjected to Cyclic Lateral Loads

D4 Procedure for determining an equivalent single-stage load spectrum

Literatur

List of Advertisers

AK 2.1 Piling Committee of the German Geotechnical Society (Deutsche Gesellschaft für Geotechnik e.V.)

Chairman until June 2013

Univ.-Prof.(em) Dr.-Ing. Hans-Georg Kempfert

Potosistraße 27

22587 Hamburg, Germany

[email protected]

Chairman (from July 2013)

Uni.-Prof. Dr.-Ing. habil. Christian Moormann

University of Stuttgart

Institute of Geotechnical Engineering

Pfaffenwaldring 35

70569 Stuttgart

[email protected]

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Members of the AK 2.1 Piling Committee of the German Geotechnical Society

At the time of publication of these recommendations the Piling Committee consisted of the following members:

Univ.-Prof. (em) Dr.-Ing. H.-G. Kempfert, Hamburg (Chairman)

Dr.-Ing. W.-R. Linder, Essen (Deputy Chairman)

Dipl.-Ing. B. Böhle, Essen

Dipl.-Ing. W. Brieke, Düsseldorf

Dipl.-Ing. G. Dausch, Mannheim

Dipl.-Ing. E. Dornecker, Karlsruhe

Dipl.-Ing. A. Ellner, Nürnberg

Dipl.-Ing. M. Glimm, Hamburg

Dipl.-Ing. R. Jörger, Wiesbaden

Dr.-Ing. O. Klingmüller, Mannheim

Dipl.-Ing. O. Krist, Munich

Univ.-Prof. Dr.-Ing. habil. Chr. Moormann, Stuttgart

Dr.-Ing. K. Morgen, Hamburg

Prof. Dr.-Ing. D. Placzek, Essen

Prof. Dr.-Ing. B. Plaßmann, Mainz

Dipl.-Ing. U. Plohmann, Eggenstein

Dr.-Ing. habil. K. Röder, Leipzig

Dr.-Ing. P. Schwarz, Munich

Dr.-Ing. W. Schwarz, Schrobenhausen

Dr.-Ing. S. Weihrauch, Hamburg

Dipl.-Ing. J. Voth, Hamburg

Further members of the Piling committee since the 1st German edition was published (2007) were:

Dipl.-Ing. W. Körner, Hamburg

Dr.-Ing. H.G. Schmidt, Ladenburg

The following subcommittees were involved in the compilation of the Pile Recommendations:

‘Dynamic Pile Testing’ subcommittee: Sections 10 and 12 and Appendix C

Dr.-Ing. O. Klingmüller, Mannheim (Convenor)

Dipl.-Ing. A. Beneke, Achim

Dr.-Ing. U. Ernst, Nuremberg

Dipl.-Ing. J. Fischer, Braunschweig

Dr.-Ing. M. Fritsch, Braunschweig

Dipl.-Ing. P. Grud, Denmark

Dipl.-Ing. G. Kainrath, Austria

Dr.-Ing. F. Kirsch, Berlin

P. Middendorp, MSc, Netherlands

Dr. rer.nat. E. Niederleithinger, Berlin

Dr. F. Rausche, USA

Prof. Dr.-Ing. W. Rücker, Berlin

Dr.-Ing. M. Schallert, Mannheim

D. Schau, Büdelsdorf

Dr.-Ing. W. Schwarz, Schrobenhausen

Univ.-Prof. Dr.-Ing. J. Stahlmann, Braunschweig

R. Skov, MSc, Denmark

Dr.-Ing. G. Ulrich, Leutkirch

Dr.-Ing. B. Wienholz, Oldenburg

‘Piled Raft and Pile Group Foundations’ subcommittee: Involved in Sections 8.1.1, 8.2.1, 8.3.1 and 8.4.1 (until 2007)

Prof. Dr.-Ing. Th. Richter, Berlin (Convenor)

Dipl.-Ing. U. Barth, Mannheim

Univ.-Prof. Dr.-Ing. R. Katzenbach, Darmstadt

Univ.-Prof. Dr.-Ing. H.-G. Kempfert, Kassel

Prof. Dr.-Ing. B. Lutz, Berlin

Dr.-Ing. Y. El-Mossallamy, Darmstadt

Dr.-Ing. H. Wahrmund, Cologne

Univ.-Prof. Dr.-Ing. habil. Chr. Moormann, Stuttgart

AK 1.4 ‘Soil Dynamics’ and AK 2.1 ‘Piles’ joint subcommittee: Section 13 and Appendix D

Univ.-Prof. Dr.-Ing. habil. S. Savidis, Berlin (Chairman AK 1.4)

Univ.-Prof. (em) Dr.-Ing. H.-G. Kempfert, Hamburg (Chairman AK 2.1)

Univ.-Prof. Dr.-Ing. M. Achmus, Hannover

Dr.-Ing. J. Dührkop, Hamburg

Dr.-Ing. H.-G. Hartmann, Frankfurt

Dr.-Ing. U. Hartwig, Stuttgart

Dr.-Ing. F. Kirsch, Berlin

PD Dr.-Ing. habil. K. Lesny, Essen

Dr.-Ing. F. Rackwitz, Berlin

Prof. Dr.-Ing. Th. Richter, Berlin

Dr.-Ing. P. Schwarz, München

Dr.-Ing. E. Tasan, Berlin

Dr.-Ing. S. Thomas, Kassel

Dr.-Ing. S. Weihrauch, Hamburg

Dr.-Ing. J. Wiemann, Hamburg

Preface of the English Version of the Recommendations of the Piling Committee of the German Geotechnical Society

(1) The present English version of the Recommendations of the Piling Committee of the German Geotechnical Society (Empfehlungen des Arbeitskreises „Pfähle“ – EA-Pfähle), is with a few exceptions a direct and complete translation of the 2nd edition 2012 of the German original. Even in case that some issues and, in particular, references might internationally not be known as in Germany, this approach was taken in order not to permit differing provisions between the German and this English version, if the latter is used in German speaking countries. It might also be possible that contractual or legal problems could arise between German and English speaking users if they could refer to a not identical translation.

(2) As outlined in Section 1, Germany has published the German language versions of the European design (e.g. Eurocode 7) and execution standards (e.g. EN 1536, EN 12699, etc.). So was EN 1997-1:2004-11: Eurocode 7: Geotechnical design – Part 1: General rules published in Germany as DIN EN 1997-1:2009-09: Eurocode 7: Entwurf, Berechnung und Bemessung in der Geotechnik – Teil 1: Allgemeine Regeln.

(3) For application in Germany, the standard DIN EN 1997-1:2009-09 was complemented with additional rules by DIN 1054:2010-12: Baugrund – Sicherheitsnachweise im Erd- und Grundbau – Ergänzende Regelungen zu DIN EN 1997-1 (Ground – Verification of the safety of earthworks and foundations) and by the National Annex EN 1997-1/NA:2010-12: Nationaler Anhang – National festgelegte Parameter – Eurocode 7: Entwurf, Berechnung und Bemessung in der Geotechnik – Teil 1 (National Annex – Nationally determined parameters – Eurocode 7: Geotechnical design – Part 1: General rules). The three documents were implemented together and their application is binding in Germany.

(4) Complementing the European execution standards, national specifications were published and implemented in Germany under the heading “DIN SPEC”.

(5) DIN 1054:2010-12: Baugrund – Sicherheitsnachweise im Erd- und Grundbau – Ergänzende Regelungen zu DIN EN 1997-1 (Ground – Verification of the safety of earthworks and foundations) frequently refers to the Recommendations of the Piling Committee of the German Geotechnical Society (EA- Pfähle) e.g. for the application of values based on well established experience for pile resistances, for the static and dynamic load testing, concerning pile resistances under cyclic loads, etc.

(6) Where this English version of the Piling Recommendations makes reference to the above mentioned German standards DIN 1054 or the DIN SPEC, the English speaking user should know, that all technical contents of the German complementing standards to Eurocode EC 7 and the European execution standards are also covered in these Recommendations.

(7) This means that the user of the Piling Recommendations (EA-Pfähle), when consequently applying, also fulfils the provisions of the complementing standards implemented in Germany.

(8) Technical terms and symbols used in these Recommendations, if in addition to those of DIN EN 1997-1 (Eurocode EC 7-1), are listed in Annex A1 and, as necessary, explained in this English version.

(9) In addition, the text can contain notes to supply the user with additional explanations for technical issues which are common in Germany or making reference to international procedures.

(10) The Piling Recommendations are technical rules representing good and generally accepted codes of practice. They are the result of technical and scientific co-operation on honorary basis of the members of the Piling Committee of the German Geotechnical Society.

Preface of the 2nd German edition

(1) Germany has a long tradition of standardisation with regard to the execution and design of piled foundations and individual pile systems. The German ‘Piles’ standardisation committee (DIN NA 005-05-07 AA) and the German Geotechnical Society’s AK 2.1 ‘Piles’ Working Group (hereafter called as the Piling Committee), have cooperated on these topics for many years, with members sitting in both bodies. In recent decades this joint committee has compiled the piling standards DIN 4026 (driven piles), DIN 4014 (bored piles) and DIN 4128 (grouted piles), and the piling section of DIN 1054 (Section 5), and adapted the individual editions to meet current best practice.

(2) Since European standardisation began at the end of the 1980s, the committee has been tasked with accompanying the development of the European execution standards EN 1536 (bored piles), EN 12699 (displacement piles) and EN 14199 (micropiles) as a national mirror committee. It was also tasked to supervise the edition of the German language versions of the execution standards, namely DIN EN 1536, DIN EN 12699 and DIN EN 14199. In terms of pile analysis and design, the committee focused on the piling sections of DIN 1054:2005-01 and DIN 1054:2010-12, paying particular attention to the partial safety factor approach.

(3) To supplement this work, the Piling Committee decided to produce summary recommendations for pile analysis and design, of which the first edition was published 2007 as ‘EA-Pfähle’ and which are presented in the second edition. The ‘EA-Pfähle’ sees itself in the tradition of similar DGGT (German Geotechnical Society) recommendations such as EAB (Empfehlungen Arbeitsausschuss Baugruben – Recommendations on Excavations), EBGEO (Empfehlungen für den Entwurf und die Berechnung von Erdkörpern mit Bewehrungen aus Geokunststoffen – Recommendations for Design and Analysis of Earth Structures using Geosynthetic Reinforcements), etc., which are now well-established as best practice regulations.

(4) With the publication of the Eurocode standards handbooks for structural engineering and the handbook for Eurocode 7, Geotechnical Design – Part 1: General Rules (1st edition 2011), European standardisation in this field has, for the time being, come to a conclusion. The standards were implemented as binding building regulations in Germany with the cut-off date 01.07.2012. The handbook Eurocode 7, Geotechnical Design – Part 1: General Rules, contains as summary DIN EN 1997-1:2009-09 (Eurocode EC 7-1: Geotechnical Design-Part 1: General Rules), DIN 1054:2010-12 (Ground – Verification of the Safety of Earthworks and Foundations – Supplementary Rules to DIN EN 1997-1) and DIN EN 1997-1/NA:2010-12 (National Annex).

(5) DIN 1054:2010-12 refers to ‘EA-Pfähle’ at various points dealing with pile analysis and design, e.g. for the tabled values for pile resistances based on well established experience. For formal reasons DIN 1054:2010-12 refers to the first edition of ‘ΕA-Pfähle’; however, it is only with the this second edition that the technical link to the EC 7-1 Handbook [44] has been properly accomplished thematically. This is especially the case for analysis methods and for terminology with regard to the EC 7-1 Handbook [44], meaning that coherent and coordinated pile foundation analysis and design regulations are now available to the user.

(6) In addition, design related issues in terms of the European pile execution standards DIN EN 1536, DIN EN 12699 and DIN 14199 are also dealt with in ‘ΕA-Pfähle’. A comparative classification of the pile systems used in construction practice (Section 2) simplifies correlation between the standards. Detailed regulations on static and dynamic pile testing (Sections 9 and 10), and quality assurance guidelines and methods (Sections 11 and 12) aim to promote technically high-quality pile construction.

(7) A new Section 13, not included in the first edition, deals with load-bearing behaviour and analysis methods for piles subjected to variable actions. Particular attention was paid to the load-bearing behaviour of piles under cyclic loads, such as often occur in foundations for wind turbines (offshore, onshore), but also in highways engineering, etc.

(8) Whereas the first edition of ‘ΕA-Pfähle’ was initially understood to be a draft, and at the time was only recommended for trial use, the draft character is no more applicable on this second edition. In the interim, the piling community has had the opportunity to test the provisions and pass on their comments and proposals to the Piling Committee. This is also the case for the new Section 13, which was previously published in a variety of organs. All statements on the first edition were dealt with by the Committee when compiling the second edition and, if justified, included. Appendices A5, A6 and D contain “informative” technical guidelines, not yet classified as best practice, but instead representing the current scientific view.

(9) In terms of the compulsory nature of the present recommendations ‘EA- Pfähle’, 2nd edition, the user is referred to the “Notes for the User” published in EAB (2006), 4th edition, Ernst & Sohn, which are applicable in a similar manner here.

(10) The German Geotechnical Society’s Piling Committee (AK 2.1 ‘Piles’ Working Group) asks to send any suggestions and correspondence concerning further development of the Recommendations to the Chairman of AK 2.1 (see Imprint for address).

Hamburg, 2012

Hans-Georg Kempfert

1

Introduction to the Recommendations and their Application Principles

1.1 National and International Regulations for Piling Works

(1) Since the implementation of DIN EN 1997-1:2009-09: Eurocode 7: Geotechnical Design – Part 1: General Rules, pile analysis and design in Germany is governed by

– Section 7 of Eurocode EC 7-1 (Eurocode 7), in conjunction with

– DIN 1054:2010-12: Subsoil–Verification of the Safety of Earthworks and Foundations – Supplementary Rules to the German version DIN EN 1997-1, and the

– National Annex to EC 7-1, namely DIN EN 1997-1/NA:2010-12: National Annex – Nationally Determined Parameters–Eurocode 7: Geotechnical Design – Part 1: General Rules.

These three coordinated documents are summarised in the German Eurocode 7 Handbook, Volume1 [44].

Note: In case amendments or corrections are made to the standards included in the German Eurocode 7 Handbook, Volume 1 [44], the changes must be adopted even when not yet incorporated in [44].

(2) In addition, the individual pile systems are governed by the following execution standards:

DIN EN 1536:

Execution of special geotechnical works – Bored piles.

DIN SPEC 18140:

Supplementary provisions to DIN EN 1536.

DIN EN 12699:

Execution of special geotechnical works – Displacement piles.

DIN SPEC 18538:

Supplementary provisions to DIN EN 12699.

DIN EN 14199:

Execution of special geotechnical works – Micropiles.

DIN SPEC 18539:

Supplementary provisions to DIN EN 14199.

DIN EN 12794:

Precast concrete products-Foundation piles.

DIN EN 1993-5:

Design of steel structures – Part 5: Piling.

(3) Because diaphragm wall elements are often employed in the same way as pile foundations, the respective execution standard must also be considered:

DIN EN 1538:

Execution of special geotechnical works – Diaphragm walls

in conjunction with:

DIN 4126:

Stability analysis of diaphragm walls.

(4) In addition, several ISO standards are being compiled for a number of special topics relating to piles. They are however not likely to be implemented as building regulations in Germany. Currently, these include:

DIN EN ISO 22477-1:

Geotechnical investigation and testing – Testing of geotechnical structures – Part 1: Pile load test by static axially loaded compression.

On a national basis, the regulations in Section 9 should be adopted for static pile testing.

1.2 Types of Analysis and Limit States using the Partial Safety Factor Approach

1.2.1 New standards generation and their application to pile foundations

(l) By European Commission decision national building design and execution standards either already have been or will in future be replaced by European standards. Actually numerous European standards have been published for geotechnical design and execution of special geotechnical works.

(2) The European standards governing pile execution are listed in 1.1.

(3) Analysis and design of pile foundations is dealt with in the European standard DIN EN 1997-1: Geotechnical Design (Eurocode 7) in conjunction with DIN 1054 and DIN EN 1997-1/NA, see 1.1. These three standards were implemented by the German Building Authorities for use in Germany as of 01.07.2012.

(4) Until the time of implementation of the Eurocodes as binding building regulations a new generation of national standards using the partial safety factor approach served as temporary solution for all fields of structural engineering. The following standards in particular represented the governing standards for pile foundations:

DIN 1055-100:2001-03:

Basis of structural design;

DIN 1054:2005-01:

Verification of the safety of earthworks and foundations;

DIN 18800:1990-11:

Steel structures and;

DIN 1045-2:2001-07:

Concrete, reinforced and prestressed concrete structures – Part 2: Concrete – Specification, properties, production and conformity – Application rules for DIN EN 206-1.

(5) These Recommendations on Piling (EA-Pfähle) are based on the standards listed in 1.1 above and, for design in particular, on Eurocode EC 7-1, in conjunction with DIN 1054 and the NA as stipulated in 1.1 (1).

1.2.2 Actions, effects and resistances

(1) The partial safety factor approach has its origins in probability theory, as used to specify the requisite safety factors from a probabilistic perspective. In contrast to this, with the implementation of DIN 1054:2005-01, the new geotechnical standards generation follows a more pragmatic split of the previously common global safety factors into partial safety factors for actions or effects, and partial safety factors for resistances.

(2) The basis for stability analyses is represented by the characteristic values for actions and resistances. The characteristic value, represented by the index “k”, is a value of which the specified probability is assumed not to be exceeded or fallen short of during the reference period, taking into consideration the design working life of the structure or the corresponding design situation. Characteristic values are generally specified based on testing, measurements, analyses or empiricism.

(3) If the “internal” or “external” pile capacity needs to be analysed, the effects at the pile head or at given depths are required:

– As action effects, e.g. normal force, shear force, bending moment;

– As stresses, e.g. compression, tension, bending stress, shear stress or equivalent stress.

In addition, further effects of actions can occur:

– As dynamic or cyclic loads;

– As change to the structural element, e.g. strain, deformation or crack width;

– As change in the position of isolated piles or pile groups, e.g. displacement, settlement, rotation.

(4) The cross-section and the internal resistance of the material are the governing factors in the design of individual components. Specific standards are to be applied for this purpose.

(5) The characteristic values of the effects are multiplied by partial safety factors, those of resistances are divided. The values acquired in this way are designated as design values of effects or resistances respectively and are characterised by the index “d”. For stability analyses, different limit states are distinguished, also see 1.2.3, 1.2.4 and 3.1.1 (4).

(6) In addition to actions, design situations are also taken into consideration for pile analyses, similar to other structural elements. To this end the previous loading cases LC 1, LC 2 and LC 3, adopted for use in analysis according to DIN 1054:2005-01, have been converted to design situations for use in analyses after DIN EN 1997-1 (EC 7-1) and DIN 1054:2010-12, and DIN EN 1990 as follows:

– BS-P (persistent (design) situation);

– BS-T (transient (design) situation) and;

– BS-A (accidental (design) situation).

In addition, there is the seismic design situation BS-E. More detailed information is given in the EC 7-1 German Handbook [44] and in [133].

1.2.3 Limit states and national application of the EC 7-1 German Handbook

(1) The term “limit state” is used with two different meanings:

a) In soil mechanics, the state of the soil in which displacements of individual soil particles against each other are so great that the mobilisable shear strength achieves its greatest values in either the entire soil mass, or at least in the region of a failure plane, is known as the “limit state of plastic flow”. It cannot become greater even if more movement occurs, but could become smaller. The limit state of plastic flow characterises the active earth pressure, passive earth pressure, bearing capacity, “external” pile failure, slope stability, and global stability.

b) A second limit state in the sense of the new safety factor approach is a state of the load-bearing structure where, if exceeded, the design requirements are no longer fulfilled.

(2) The following limit states are differentiated using the partial safety factor approach:

a) The ultimate limit state is a condition of the structure which, if exceeded, immediately leads to a calculated collapse or another form of failure. It is referred to as “ULS” in EC 7 and DIN 1054. Further distinguishing is described in (5).

b) The serviceability limit state is a condition of the structure which, if exceeded, no longer fulfils the conditions specified for its use. It is referred to as “SLS” in EC 7 and DIN 1054.

(3) For ultimate limit state analysis (ULS), Eurocode EC 7-1 provides three options. With one exception (see (6) and (9)), the supplementary rules of DIN 1054 for use in Germany are based on Analysis Method 2 of EC 7-1. The partial safety factors are applied to both, effects and resistances. To differentiate this from the other permitted scenario, in which the partial safety factors are not applied to the effects but to the actions, this procedure is designated as Analysis Method 2* in [133], also see the EC 7-1 Handbook [44].

(4) The National Annex to EC 7-1 and DIN 1054 represent a formal link between EC 7-1 and national German standards, see EC 7-1 German Handbook [44]. In DIN 1054 and the National Annex it is stated which of the possible analysis methods and partial safety factors are applicable in the respective national domains. In addition, the applicable, supplementary national codes may also be given. The supplementary national codes may not contradict EC 7-1. Moreover, the National Annex may not repeat information already given in EC 7-1.

(5) Eurocode EC 7-1 distinguishes the following subordinate limit states of the ultimate limit state (ULS):

a) EQU: Loss of equilibrium of the structure, regarded as a rigid body, or the ground. The designation is derived from “equilibrium”.

b) STR: Internal failure or very large deformations of the structure or its structural elements, where the strength of the materials governs the resistance. The designation is derived from “structural failure”.

c) GEO: Failure or very large deformation of the structure or the ground, where the strength of the soil or rock governs the resistance. The designation is derived from “geotechnical failure”.

d) UPL: Loss of equilibrium of the structure or the ground due to buoyancy or water pressure. The designation is derived from “uplift”.

e) HYD: Hydraulic ground failure, internal erosion of or piping in the ground, caused by a flow gradient. The designation is derived from “hydraulic failure”.

(6) In the terminology of the EC 7-1 German Handbook [44] the GEO limit state is sub-divided into GEO-2 and GEO-3:

a) GEO-2: Failure or very large deformation of the ground in conjunction with the calculation of the action effects and the dimensions, i.e. when utilising shear strength for passive earth pressure, for sliding resistance and bearing resistance, and when analysing deep slide surface stability for anchored retaining walls, and for base resistance and skin friction of pile foundations. The GEO-2 limit state calculation follows Analysis Method 2*, see (3), as outlined in the EC 7-1 German Handbook [44].

b) GEO-3: Failure or very large deformation of the ground in conjunction with the analysis of the overall stability, i.e. when utilising the shear strength for analysis of the safety against slope failure and global failure and, normally, when analysing slope stabilisation measures, including consideration of structural elements, e.g. anchors or piles. The GEO-3 limit state calculation follows Analysis Method 3 as outlined in the EC 7-1 German Handbook [44].

(7) The EQU, UPL and HYD limit states describe the loss of static equilibrium. These include:

a) Safety analysis against overturning (EQU);

b) Safety analysis against buoyancy or uplift, e.g. of a tension pile group (UPL);

c) Safety analysis against hydraulic heave (HYD).

(8) The limit states EQU, UPL and HYD involve actions only, but no resistances.

The governing limit state condition is:

(1.1)

i.e. the destabilising actions Fk, multiplied by the partial safety factor γdst, ≥ 1, 0, may only be as large as the stabilising action Gk, multiplied by the partial safety factor γstb < 1, 0.

(9) The GEO-2 limit state describes the failure of structures and structural elements or the failure of the ground. It includes:

a) Analysis of the bearing capacity of structures and structural elements subjected to loads from the ground or supported by the ground;

b) Analysis of the bearing capacity of the ground to demonstrate that it is not exceeded, e.g. passive earth pressure, bearing resistance, pile resistance or sliding resistance.

The analysis to demonstrate that the bearing capacity of the ground is not exceeded is performed exactly as for any other construction material. The limit state condition is always the governing condition:

(1.2)

i.e. the characteristic effect Ek, multiplied by the partial safety factor γF for actions or strains, may only become as large as the characteristic resistance Rk, divided by the partial safety factor γR.

(10) The GEO-3 limit state is a peculiarity of earthworks and ground engineering. It describes the loss of overall stability. It includes:

a) Analysis of safety against slope failure;

b) Analysis of safety against global failure.

The limit state condition is always the governing condition:

(1.3)

i.e. the design value Ed of the effects may only become as large as the design value of the resistance Rd. The geotechnical actions and resistances are determined using the design values for shear strength:

(1.4a)

(1.4b)

i.e. the friction tan φ and the cohesion c are reduced from the outset using the partial safety factors γφ and γc.

(11) The serviceability limit state (SLS) describes the state of a structure or structural element at which the conditions specified for its use are no longer met, but without loss of its bearing capacity. The analysis is based on the anticipated displacements and deformations being compatible with the purpose of the structure.

1.2.4 Transitional regulations for applying of the Recommendations on Piling in conjunction with the EC 7-1 German Handbook

(1) These Recommendations on Piling are based on the provisions of the EC 7-1 German Handbook [44].

(2) A decisive difference between the provisions of the EC 7-1 German Handbook [44] and DIN 1054:2005-01 is the specification of different partial safety factors γP (lower) and the correlation factors ξ (higher) for pile foundations. Overall, however, γP and ξ result in a comparable magnitude on the resisting side, like DIN 1054:2005-01, see [59].

(3) The existing limit states to DIN 1054:2005-01 are replaced as follows in the EC 7-1 German Handbook [44]:

a) The previous GZ 1A limit state to DIN 1054:2005-01 corresponds without restrictions to the EQU, UPL and HYD limit states as in the EC 7-1 German Handbook [44].

b) The previous GZ 1B limit state to DIN 1054:2005-01 corresponds without restrictions to the STR limit state as in the EC 7-1 German Handbook [44] as the “internal” pile capacity (material strength). In addition, there is the GEO-2 limit state as in the EC 7-1 German Handbook [44], in conjunction with the “external” design of the foundation elements, e.g. the “external” pile capacity.

c) The previous GZ 1C limit state as in DIN 1054:2005-01 corresponds to the GEO-3 limit state as in the EC 7-1 German Handbook [44], in conjunction with the analysis of the overall stability, i.e. when utilising the shear strength for analysis of safety against slope failure and global failure.

1.3 Planning and Testing Pile Foundations

(1) These Recommendations use the terms “designer” (planner) as the EC 7-1 German Handbook [44] and the EC 7-2 German Handbook [45].

(2) The designer should consult a specialist pile foundation planner if not in possession of the requisite knowledge and experience for pile foundation planning.

(3) A geotechnical design report must be compiled for pile foundations in accordance with the EC 7-1 German Handbook [44], which must make reference to the ground investigation report in accordance with the EC 7-2 German Handbook [45].

(4) Pile foundations are classified as either Geotechnical Category GC 2 or Geotechnical Category GC 3. See 3.2 and the EC 7-1 German Handbook [44] for classification criteria.

(5) Where pile foundations are classified as Geotechnical Category GC 3, a geotechnical expert with requisite experience must be consulted during the structural engineering appraisal of the ground investigation report and the geotechnical design report. In particular, the geotechnical expert should verify the ground model, the soil parameters and the design approach, and, in agreement with the independent verifier, should carry out comparative analyses.

(6) The execution of pile foundations should be supervised by a specialist planner or a geotechnical expert with the requisite experience and specialist knowledge of pile foundations. Where pile foundations are classified as Geotechnical Category GC 3, the expert mentioned in (5) must also be consulted to check the detailed design and to supervise the pile execution works.

2

Pile Systems

2.1 Overview and Classification into Pile Systems

(1) The available pile systems, highly variable in their structure and their application options, differentiate between three groups in accordance with the respective execution standards, see Figure 2.1:

a) Bored piles to DIN EN 1536 and DIN SPEC 18140:

Bored piles are characterised by ground being loosened and transported during installation. The excavated ground volume can correspond to the total or part of the pile volume.

DIN EN 1536 applies to vertical and inclined bored piles with rakes up to 4:1 (3:1 if the casing remains in place), and diameters between 0,3 m and 3,0 m, and a depth to diameter or width ratio ≥ 5.

The system adopted in the standard differentiates bored piles according to the type of support of the borehole and the methods used for excavation, concreting and reinforcement installation. The combinations are summarised in Table 2.1.

– Unsupported excavation is suitable for installing piles in stable ground (for the duration of pile installation). These piles are generally bored using intermittent excavation methods (Kelly operated augers or buckets or with cable grabs and shells) and concreted in dry conditions. The reinforcement can be placed before or after concreting. The piles can be underreamed to form enlarged bases or, in special cases, be provided with shaft enlargements.

– Cased excavation is suitable for installing piles in unstable ground and for boring below the groundwater table. Excavation is either intermittent as described above, or continuous, e.g. using continuous flight augers or flushing for soil removal (the latter is less common for pile construction in Germany). The piles can be installed with enlarged bases and, for greater depths, be telescoped, i.e. with stepwise reduced diameter at increasing depth. The concrete is placed using a tremie pipe. The concrete may only be placed under the same conditions as for dry concreting if groundwater ingress to the bore can be ruled out. The reinforcement can be placed before or after concreting. The casing is either temporary and is removed during concreting, or can be required permanently, e.g. in free water, where groundwater flow is strong or high groundwater or ground aggressivity to concrete.

– Excavation under a supporting fluid is possible for the same ground conditions as for cased excavation and generally the same excavation tools are employed. In addition to circular piles, rectangular, T, L or cruciform section piles can be constructed. Non-circular piles (barettes) are constructed using diaphragm wall techniques. Stability analysis for the fluid supported borehole and quality control for the fluid must be performed as for diaphragm wall methods

– Soil supported piles, i.e. continuous flight auger piles with soil-filled flights. Augers with large and small hollow stem diameters are differentiated, also see 2.2.1.4. During boring, the auger helix fills with loosened ground material. This material supports the borehole wall and is transported upwards on the helix flights. If augers with small diameter hollow stems are employed, the concrete is pumped through the hollow stem as the auger is extracted. The reinforcement cage is inserted after concrete placement into the fresh concrete and the auger is completely withdrawn. Excavation material accumulated on the auger flights is removed while the auger is retracted. When using augers with large diameter hollow stem, the reinforcement cage is generally inserted into the hollow stem after completion of excavation and prior to concreting. Piles installed using a large diameter hollow stem are also known as “partial displacement piles”, because only part of the volume of the excavated ground is transported to the surface and the remainder is displaced into the surrounding ground. The partial displacement pile subgroup includes those systems with boring tools possessing a continuous auger only along their bottom lengths. When boring into load-bearing ground, excavated material can be at least partially redistributed to the overlying strata. When retracting the auger, the soil material remaining on the helix flights is transported to the surface.

b) Displacement piles to DIN EN 12 699 and DIN SPEC 18538:

Displacement piles are characterised by being installed without excavation or removal of soil material – except to limit heave or vibrations, to remove obstacles or as an installation aid.

The soil accumulating at the surface when installing displacement piles is the result of the displacement effect and the lack of soil surcharge close to the surface. It does not represent relevant soil removal.

The minimum pile diameter or corresponding cross-sectional dimensions are currently specified in DIN EN 12699 as 150 mm.

Note: This limit will be dispensed within the current revision of this standard.

The displacement pile group differentiates:

– Prefabricated piles consisting of reinforced concrete, prestressed concrete, steel, cast iron or timber;

– Driven cast-in place concrete piles;

– Grouted displacement piles;

– Screw piles (full displacement piles). These are pile systems in which the drive tube enters the ground through rotation and downward pressure by means of a displacement head located at the lower end, without relevant soil transport or redistribution from the embedment zone in the load-bearing stratum into the overlying strata.

Figure 2.1 Overview of pile systems standardised in the pile execution standards DIN EN 1536, DIN EN 12 699 and DIN EN 14 199

Note: During boring, displacement pile systems employing boring tools possessing more than one helix in the base region can redistribute soil out of the load-bearing stratum and into the overlying stratum. When retracting the boring tool, the soil material remaining on the helix is extracted from the bore. These effects must be taken into consideration in the design. They can result in a reduction of bearing capacity compared to “full displacement piles”. No empirical pile resistance data are given in Section 5 for these pile systems.

c) Micropiles to DIN EN 14199 and DIN SPEC 18539:

At the current stage of standardisation the diameter range of bored micropiles is less than 0,30 m, and less than 0,15 m for displacement piles. The load transfer from micropiles to the surrounding soil is achieved through skin friction mainly.

This group differentiates:

– Cast-in-situ piles with small reinforcement cages and using fine-grained concrete or grout, for which cased or slurry-supported pile construction methods are generally employed;

– Composite piles, which possess a tendon or tubular bearing element encased in a cement grout sleeve and;

– Precast piles (< 0,15 m) with or without subsequent grouting.

Note During the current revisions of EN 12699 and EN 14199 the diameter restriction shall be abolished for displacement and all displacement piles shall be covered by EN 12699. Consequently, DIN EN 14199 shall in future cover only bored micropiles.

2.2 Pile Construction

2.2.1 Bored piles

2.2.1.1 Cased bored piles

(1) When constructing cased bored piles, the soil is loosened and extracted within a casing. Reinforcement can then be placed and concrete is cast into the temporary, cased void. Installation complies with DIN EN 1536, also see [80] and [136].

(2) The casing can be installed in a number of different ways:

– By rotation either back and forth (oscillation) or in one direction (rotation) together with axial advance using a casing rig or casing rotator;

– Using the rotary head of a rotary rig;

– Using a piling or a vibrating hammer.

(3) For large depths and high skin friction values, a telescopic casing sequence can be employed. Boring is started using the largest diameter. Before reaching the capacity of the casing rig, the first casing is held in position and boring continues using a smaller diameter casing.

(4) In unstable ground the casing shall be installed in advance of the excavation. Only in firm, or at least temporarily stable, ground excavation may advance ahead of the casing. At its bottom, the casing is equipped with a cutting shoe with special, hardened teeth, which overbreak the bore slightly to reduce friction on the casing wall.

(5) The ground can be loosened and extracted in different ways:

– Discontinuously, using rotary excavation methods and rotary rigs with Kelly bar-driven augers, drilling buckets and coring tools;

– Discontinuously using grabbing methods with grabs, gravel pumps or chisels operated with cable cranes;

– Continuously using continuous flight auger (double rotary drilling method);

– Continuously using a drag or roller bit and flush boring.

(6) Using double rotary drilling, the boring tool is advanced into the ground together with the casing whilst being constantly rotated, whereby the soil is loosened by the augering tool and conveyed upwards on the helix flights.

(7) When using boring methods with direct or reverse flushing, the ground is constantly loosened by the roller or drag bit. Material is transported by means of air and/or water flushing. These boring methods are widespread in Germany for installing deep wells or for geothermal energy bores, but rarely for the construction of piles.

(8) The principles described in 11.2.1 shall be followed in order to avoid loosening of the surrounding ground. A reinforcement cage is generally inserted after reaching the final depth, and the pile is concreted using a tremie pipe while simultaneously the casing is withdrawn. However, the reinforcement cage can also be inserted after concreting into the fresh concrete column (e.g. when using the double rotary drilling method).

(9) Special cutting tools are used to produce enlarged pile bases. As they cannot be used inside casings, enlargements can be constructed only in stable ground or ground supported otherwise in the zone of the pile base.

(10) Cased bored piles are constructed with shaft diameters up to 2,5 m, in special cases even larger. The standard range lies between 0,6 m and 1,8 m. Depths up to approximately 60 m can be achieved, depending on the ground conditions and pile diameter. Measures as described in (3) can be necessary for greater depths.

(11) The characteristic pile resistances in the serviceability limit state are in the order of 1 MN to 10 MN, depending on diameter and ground conditions. They can be higher for larger diameters and favourable ground conditions.

(12) Because of their high flexural rigidity, large diameter piles, in particular, can transmit considerable horizontal loads in suitable ground.

(13) Cased bored piles can be installed in all soil types including rock (with limitations). Obstacles can be penetrated using special tools (chisels, rock augers and buckets, core barrels).

2.2.1.2 Unsupported excavations

(1) In sufficiently stable ground bored piles can be constructed without a casing or other bore support.

(2) In such cases, a protective casing is only necessary for stabilisation of the top of the bore and for guidance of the tools.

(3) If unstable strata are penetrated, this length of the bore shall be supported.

(4) This installation method should only be employed for vertical and raked piles up to an inclination of 15:1.

2.2.1.3 Fluid-supported excavations

(1) Bored piles constructed under a fluid support can have either circular cross-sections or cross-sections composed of rectangles. The latter are also known as barettes. Bentonite suspensions are generally employed as support fluids to stabilise the bore walls.

(2) When work commences, a lead-in tube (circular) is placed or a guide wall (barette) installed. The soil is then excavated under the support fluid. The fluid level within the bore must at all times remain at a level within the leader pipe or the guide walls, such that sufficient positive pressure is exercised on the bore wall. The stability of the fluid-supported bore shall be analysed compliant with DIN 4126. A reinforcement cage is generally inserted after reaching the final depth, and concrete is subsequently placed by tremie method.

(3) Circular cross-sections are generally excavated using the discontinuous boring tools described above. Diaphragm wall grabs or hydro fraises are generally used to construct non-circular cross-sections.

(4) Circular piles are executed with diameters up to approximately 3 m or as rectangular barettes (see 2.2.1.7) with widths between 0,4 m and 2,0 m, and lengths between 2,4 m and 7 m. Cross-sections composed of rectangles, e.g. T-sections, are also possible.

(5) Due to the large possible cross-sectional dimensions, these piles can support very large vertical and horizontal loads. Pile lengths in excess of 60 m are possible.

(6) The method is also suitable for construction of primary supports (e.g. plunged columns) when using top-down execution methods. These are vertical structural elements which support floor slabs and building loads when structures or basements are built downwards without excavation pits. The primary supports consist of cast-in-place piles below the basement level and prefabricated steel, reinforced concrete or composite columns within the basement.

2.2.1.4 Soil-supported, continuous flight auger bored piles

(1) Soil-supported, continuous flight auger bored piles are constructed by rotating a continuous flight auger into the ground and pumping in concrete as the auger is retracted. The piles can be installed with or without reinforcement. Installation is vibration-free.

(2) These pile systems are also known as auger piles. Augers with large and small hollow stem diameters are differentiated. Augers with small hollow stems generally have internal vs. external hollow stem diameters of Di/Da < 0,4 and such with large hollow stems of Di/Da > 0,6 (partial displacement bored piles).

(3) Common auger diameters range between 0,4 m and 1,2 m.

(4) Continuous flight augers piles with large diameter hollow stems are also known as partial displacement piles, also see 5.4.7 and 11.2.6. These piles laterally displace some of the soil. The extracted soil volume should not exceed approximately 70% of the pile volume.

(5) During boring, the bore wall is supported by the soil being transported upwards on the auger helix. The advance speed and rotation speed of the auger must be adapted to suit the ground conditions in order to limit soil extraction and thus retain the ground support.

(6) During boring, the hollow stem must be sealed, e.g. by an expendable end plate to ensure it remains free of soil material and water.

(7) When using augers with small hollow stem diameter and resultant geometrical constraints, a reinforcement cage can only be inserted into the fresh concrete after the pile is concreted. In contrast, when using augers with a large hollow stem diameter, a reinforcement cage can be installed inside the hollow stem prior to concreting.

(8) To prevent soil transport from the auger downwards into the fresh concrete, the auger should be retracted without rotating, or only rotated slightly in the same direction as used for boring.

(9) In accordance with DIN EN 1536, continuous flight auger bored piles should not be installed in uniform, non-cohesive soils (d60/d10< 1,5) below the groundwater table, or in loose, non-cohesive soils with densities D < 0,3 or in soft, cohesive soils with undrained shear strengths cu< 15 kN/m2, unless the feasibility of the installation method has been demonstrated on test piles or through local experience before commencing works. The standard also points out that uniform, non-cohesive soil where 1,5 < d60/d10 < 3,0 can be sensitive when situated below the groundwater table.

(10) The characteristic pile resistances in the serviceability limit state are in the order of 0,5 MN to 2 MN, depending on the pile diameter and ground conditions.

2.2.1.5 Soil-supported, partial flight auger bored piles

(1) Partial flight augers piles and large diameter hollow stem piles are also known as partial displacement piles, also see 5.4.7.

2.2.1.6 Bored piles with enlarged bases

(1) It can be expedient to enlarge the pile base if the capacity of the pile relies entirely or predominantly on the base resistance, or if pile bases rest on a load-bearing stratum and/or only slightly embedded in the stratum. In addition, an enlarged base allows improved utilisation of concrete strengths, and thus allows material savings in the pile shaft, because the adopted base resistances are generally considerably lower than the concrete strengths.

(2) Ground improvement measures executed around the base region of a pile, such as jet grouting, deep vibration or similar methods are not understood as enlarged bases.

(3) Enlarged bases can only be installed in stable soils or soils that can be suitably stabilised for the purpose, e.g. using bentonite suspension or cement slurry.

(4) Construction of enlarged bases is generally only possible for vertical piles and in cased pile bores, and requires special belling-out tools; these include special, extended belling buckets attached to the Kelly bar and fitted with retractable reaming wings. The reaming wings can generally be extended by the advance of the Kelly bar in conjunction with a scissor mechanism inside the belling bucket. The rate of advance correlates to the extension of the wings and can therefore be controlled. For structural reasons, the reaming wings are arranged slightly above the base of the belling bucket, and this section of the bucket is designed to accept the loosened spoil. The shape of an enlarged base therefore corresponds to a truncated cone with a spherical base and a lower, cylindrical protrusion.

(5) When constructing an enlarged base, boring is carried out first using one of the tools described in 2.2.1.1 (e.g. a standard drilling bucket), such that the reaming wings of the belling-out bucket can later operate from the design bottom level of the base enlargement. The casing is then retracted as far as the top of the reaming wings and, if necessary, the now uncased lower section of the bore stabilised. The Kelly bar with the reaming tools is then inserted into the bore, and the enlarged base (bell) is produced by rotating the bucket and conically milling the uncased bore wall. Depending on the required size of the enlargement and the amount of milled material present in the lower section of the bucket, the reaming tool must be retracted and emptied, and the enlarging process continues repeatedly.

(6) The bore is cleaned after enlarging, the reinforcement inserted and the pile concreted. The enlarged section must be concreted without interruption up to the inside of the casing, as there would be otherwise a danger of entrapment of soil and other materials.

(7) In case of the enlarged base the conical section protruding outside the diameter of the cylindrical pile shaft is left unreinforced. Load distribution from the shaft into the base area is achieved solely by shear strength of the concrete. This load distribution and the stabilisation of the overhanging bell wall are the reasons for the geometric limitations of the bell and the restriction in the base diameter in relation to the shaft diameter.

(8) See 5.5 for the base resistances for piles with enlarged bases.

2.2.1.7 Diaphragm wall elements/barettes

(1) Diaphragm wall elements/barettes are bored piles compliant with DIN EN 1536, if:

– They are concreted in a single process;

– They have square, rectangular, T- or L-shaped, or similar cross-sections;

– The shortest side measures Wi ≥ 0,4 m;

– The ratio of the largest dimension Li to the smallest dimension Wi of the element is Wi/Li ≤ 6;

– The smallest dimension of precast concrete elements installed within diaphragm wall elements measures Dp ≥ 0,3 m or Wp ≥ 0,3 m (Dp being the diameter of a round precast element and Wp the smaller side of a rectangular precast element) and;

– The overall cross-sectional area is smaller than 15 m2.

2.2.2 Prefabricated driven piles

2.2.2.1 Introduction

(1) Prefabricated driven piles to DIN EN 12699 comprise prefabricated pile elements of reinforced concrete, prestressed concrete, steel or timber, which completely displace the soil when driven or pressed into the ground, thereby generally displacing and compacting it. The piles are manufactured off-site with full length or in sections, transported to the site and driven using suitable equipment. Prefabricated driven piles can be installed vertically or at rake. Depending on the required foundation depth, piles delivered in sections must be extended using couplings or by welding.

(2) As a result of the displacement effect and the method of installation, which acts like dynamic or static pile loading, only minor settlement or heave of the completed pile is required to mobilise the pile’s external capacity.

2.2.2.2 Precast driven concrete piles

(1) Precast driven reinforced concrete piles mostly have square cross-sections of 20 × 20 cm to 45 × 45 cm. Less frequently spun concrete piles are employed as round piles of similar dimensions but with a hollow cross-section. The piles are reinforced or prestressed for loads acting during transport and installation, and for the loads of the superstructure (compression, tension, bending). For usual applications, precast concrete piles are produced in lengths between 6 m and 15 m, in exceptional cases up to approximately 25 m. For pile lengths greater than 15 m it is more practical to join sections using tested and approved steel couplings. As result, the piles can be extended almost without limit; precast driven concrete piles up to a length of 80 m have been installed. Special purpose piles can be fitted with embedded grouting tubes for postgrouting (e.g. to increase capacity).

2) Today, precast driven concrete piles are generally percussion driven (hydraulic hammer, diesel hammer, drop hammer). A driving helmet containing a buffer material such as wood, plastic or similar material is located between the driving ram and the pile. Because of the mechanical loads imposed during driving, concrete C 50/60 or higher is used, which is suitable for exposure classes XC 4 to XS 3. The piles are reinforced and contain horizontal links along their whole length to resist the driving forces (compression, tension splitting). About 1 m lengths at both pile or section ends, the reinforcement links are at closer intervals. The piles can be manufactured with a driving shoe, but normally the head and the base are both formed with similarly flat ends. If driving is in hard ground or rock, a steel tip can be cast in the concrete; this is generally necessary for spun concrete piles.

(3) The characteristic pile resistances of precast concrete driven piles in the serviceability limit state are in the order of 0,5 MN to 2 MN, depending on the cross-section and ground conditions.

2.2.2.3 Prefabricated driven steel and cast-iron piles

(1) Steel piles are formed from either H-sections, steel tubes, joined sections or sheet piles with a variety of cross-sections and wall thicknesses. For increase of base resistance, reinforcement of pile bases such as plates or wings are welded on as required.

(2) Driving is in general like that for concrete piles. For hard driving and to prevent bulging and buckling, the pile head is also reinforced. For reasons of economy, steel piles are mainly used where their comparatively high tensile strength and durability can be properly exploited, for example in offshore or harbour facilities, occasionally also where high tensile loads need to be transferred.

(3) The characteristic pile resistances of steel piles in the serviceability limit state are in the order of 0,5 MN to 2 MN, depending on the cross-section and ground conditions.

(4) Prefabricated driven cast-iron piles, also referred to as ductile piles, consist of ductile, spun cast pipes, driven to the load-bearing stratum with the aid of a hydraulic hammer. Because of the low mass of the cast-iron pipes, they can be installed using smaller equipment.

(5) The generally 5 m long pipe segments are fitted with conical sleeves, allowing them to be connected to make up the required pile length during driving. The driving process creates a rigid, frictional bond within the sleeves. Special care must be taken to ensure that the pipe sections are aligned axially to prevent damage during the driving process.

(7) Ductile piles can be constructed with or without grouting.

(8) If executed without grouting, the leader pipe driving shoe is of the same diameter as the cast-iron pipe. This pile type is generally used as an end-bearing pile on very firm bearing strata.

(9) If the pile is executed with shaft grouting, an oversize pile shoe projecting in radius approximately 40 mm is used. During driving, cement grout or finegrained concrete is permanently pumped to the pile base through the inside of the pipe and fills the annulus formed by the oversize pile shoe. This pile type is generally used in non-cohesive and cohesive ground.

(10) The characteristic pile resistances of ductile piles in the serviceability limit state are order of 0.5 MN to 1,1 MN, depending on the cross-section, kind of construction and ground conditions.

2.2.2.4 Prefabricated driven timber piles

(1) Timber piles only play a subordinate role in today’s construction practice. They are predominantly used for temporary construction measures, e.g. as foundations for falsework, etc. Because of the disadvantages presented in terms of material and the comparatively low bearing capacity, they are very rarely used as foundations for structures. Timber piles are also employed for aesthetic reasons, e.g. as retaining walls along river banks or lake shores, for terracing terrain in landscaping, or for light foundations, e.g. in nature conservation areas.

(2) Timber piles are manufactured as round piles with diameters between 15 cm and 35 cm and can be reinforced at the head (driving band) and base (shoe) for driving. Normally, light driving rigs with drop weights up to 1 t maximum are used with timber piles.

(3) The characteristic pile resistances of timber piles in the serviceability limit state range from 100 kN to 600 kN, depending on the cross-section, length and ground conditions.

2.2.3 Cast-in-place concrete piles

2.2.3.1 Cast-in-place concrete piles with internal driving tube (Franki pile)

(1) The Franki pile is a cast-in-place concrete pile with internal tube driving to DIN EN 12699 and is installed with an enlarged pile base.