ASPECTS OF STANDARDIZATION FOR PILES IN EUROPE Roger Frank, Université Paris-Est, Ecole nationale des ponts et chaussées, Navier-CERMES, Marne-la-Vallée, France, Tel: +33 1 64 15 35 43, E-mail: frank@cermes.enpc.fr Abstract After noting the importance of standardization for piles, the European system is described (execution, tests and design, etc.). Some important aspects of Eurocode 7 are outlined (like the role of pile load tests). Finally, the calculation methods in the recent French standard for the design of piles following Eurocode 7 are shortly addressed. Importance of standardization for piles Like for other fields of geotechnical engineering, pile engineering is a complex art. For piles, the challenges are particularly numerous and many things must be mastered properly: - the soil investigation must be serious and adequate (for instance, deep enough!); - the choice of the pile type and the assumed behaviour must be assessed in order to reach a safe and economic design of the overall foundation; - the execution itself (construction and/or installation) deserves special attention and must follow strict state-of-the art rules. The geotechnical engineer, in charge of the design of a pile foundation, must have in mind the parameters linked to the variety of soils, of soil conditions and of pile types. A wide range of strong environmental issues are also to be considered: minimum disturbance during the execution processes, long-duration friendliness of the “inclusions” into the ground (to avoid pollution of the soils and waters, for instance) and respect of the neighbouring structures. Pile engineering plays in a world which is constantly moving and progressing: constructions expand in new difficult areas, actions on piles are more and more important, new execution techniques of piles are developed, research into the complex behaviour of pile foundations has no end, etc. Our views on how piles and group of piles really work are constantly evolving! All these facts show the need for careful guidance about what is already “agreed” by the specialists. In the area of pile engineering, the assurance of quality is particularly needed. In most countries, codes and/or standards and/or recommendations dealing with pile foundations have been (or are being) developed in order to deal with a threefold challenge: testing, design and execution. Very often, the codes of practice for piles are comprehensive, in the sense that they deal with the three subjects in a unique document. The International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE), the pre-eminent learned society for geotechnical practitioners and researchers, has two technical committees dealing with piles: TC 212 “Deep foundations” at the international level (Chair : Rolf Katzenbach) and ERTC 3 “Piles” at European level (Chairs: Maurice Bottiau and Noël Huybrechts). The committee ETC10 “Evaluation of Eurocode 7” should also be mentioned here (Chair: Trevor Orr). The aim of the 3 committees is to exchange knowledge, gather information or draft recommendations, in particular, for pile practice. They have organised several successful international conferences, symposia and workshops.

Standardization system for piles in Europe In Europe, we rely more and more, on standards/norms drafted under the auspices of the CEN (Comité Européen de Normalisation = European Standardization Committee). The three subjects are treated in different documents and are prepared by different committees (CEN/TCs). For pile engineering, the European standards thus fall into the three categories: - geotechnical design: Eurocode 7 – Parts 1 and 2 (CEN/TC 250/SC7, Chair: Andrew Bond); and Eurocode 8-Part 5 for seismic design (CEN/ TC 250/ SC 8, Chair: Eduardo de Carvalho); - execution of special geotechnical works (CEN/TC 288, Chair: Christian Gilbert); - geotechnical investigation and testing (CEN/TC 341, Chair: John Powell). Eurocode 7 is certainly now the leading document for geotechnical construction throughout Europe. Eurocode 7 consists of two parts: EN 1997-1 Geotechnical design - Part 1: General rules (CEN, 2004); EN 1997-2 Geotechnical design - Part 2: Ground investigation and testing (CEN, 2007). As far as execution works are concerned, TC 288 has already published 13 standards (some of them are applicable in Europe for a number of years now). Their references are (update: June 2013) EN 1536: 2010 Bored piles EN 1537: 2013 Ground anchors EN 1538: 2010 Diaphragm walls EN 12063: 1999 Sheet-pile walls, confirmed in 2010 EN 12699: 2000 Displacement piles, under revision EN 12715: 2000 Grouting, confirmed in 2010 EN 12716: 2001 Jet grouting, confirmed in 2011 EN 14199: 2005 Micropiles, under revision EN 14475: 2006 Reinforced fill, confirmed in 2011 EN 14490: 2010 Soil nailing EN 14679: 2005 Deep mixing, confirmed in 2010 EN 14731 2005 Ground treatment by deep vibration, confirmed in 2010 EN 15237: 2007 Vertical drainage, confirmed in 2012 For more details on the execution standards of TC 288, see the companion paper by Gilbert (2014). In the original work programme of CEN/ TC 341, the following standards for tests on piles are mentioned (Work Group 4, Convenor Jean-Paul Magnan): prEN ISO 22477-1 Pile load test – static axially loaded compression test; prEN ISO 22477-2 Pile load test – static axially loaded tension test; prEN ISO 22477-3 Pile load test – static transversally loaded test. To date (January 2014), it seems that only the standard for the static pile load test in compression (prEN ISO 22477-1) has been fully drafted and is presently ready to enter into the process of enquiry before the final vote by the members of CEN (the National Standard Bodies). Working Group 7 was recently created in order to take on board the two following standards (Convenor: Paul Hoelscher): prEN ISO 22477-4 Pile load test - dynamic axially loaded compression test prEN ISO 22477-X Pile load test - rapid axially loaded compression test (for which a first working document exists since August 2010). A close link is maintained between the 3 series of documents by careful cross-referencing, where appropriate. Eurocode 7-Part 1 “Geotechnical design – general rules” clearly requires in Section 7 “Pile foundations”, for instance, that the standards for the execution of piles should be applied (clause 7.1(3)P).

It is worth mentioning here a recommendation from Eurocode 7, particularly relevant to pile engineering (clause 2.4.1 in Part 1): ‘(2) It should be considered that knowledge of the ground conditions depends on the extent and quality of the geotechnical investigations. Such knowledge and the control of workmanship are usually more significant to fulfilling the fundamental requirements than is precision in the calculation models and partial factors.’ Important aspects of Eurocode 7 for pile design Section 7 “Pile foundations” is very well developed. The core of Section 7 of Eurocode 7 (CEN, 2004) is devoted to the behaviour of pile foundations under axial (vertical) loads. An innovative concept introduced in this section, with regard to traditional pile design, is the use of correlation factors ξ for deriving the characteristic compressive and tensile resistances of piles either from static pile load tests or from ground test results. In both cases, the correlation factor ξ depends mainly on the number of tests performed, whether pile load tests or profiles of ground tests. In the recent French standard for the design of piles following Eurocode 7 (AFNOR, 2012), the values of the correlation factor ξ also take into account the density of the tests, through the influence of the area of investigation In Eurocode 7 – Part 1, Section 7, clause 7.6.2.2 applies to the 'Ultimate compressive resistance from static load tests', clause 7.6.2.3 applies to the 'Ultimate compressive resistance from ground test results', in particular, clause 7.6.2.3(5)P and Equation 7.8 for the 'model pile' method, and clause 7.6.2.3(8) for the 'alternative' method, clause 7.6.4 deals with the vertical displacements of pile foundation (Serviceability of supported structures) and clause 7.7 deals with ‘Transversely loaded piles’. Detailed comments are given, for instance, in Frank et al. (2004) and in Bond and Harris (2008), as well as in the companion paper by Seters (2014). In Eurocode 7, the importance of static load tests is clearly recognised as the basis of pile design methods. The methods accepted by Eurocode 7 for the design of piles must nearly all be based, directly or indirectly, on the results of static pile load tests. The document clearly states that (clause 7.4.1(1)P): "The design shall be based on […]: - the results of static load tests, […] - empirical or analytical calculation methods whose validity has been demonstrated by static load tests […] - the results of dynamic load tests whose validity has been demonstrated by static load tests […] - the observed performance of a comparable pile foundation, provided that this approach is supported by the results of site investigation and ground testing." Pile load tests shall be carried out (clause 7.5.1(1)P): - when using a new type of pile or installation method; - when there is no comparable soil and loading conditions; - theory and experience do not provide sufficient confidence in the design; - installation indicate pile behaviour that deviates from the anticipated behaviour and additional ground investigations do not clarify the reasons. The static pile load test procedure (clause 7.5.2.1(1)P) "[…] shall be such that conclusions can be drawn about the deformation behaviour, creep and rebound […]. For trial piles, the loading shall be such that conclusions can also be drawn about the ultimate failure load”. For tension piles, the tests should be carried out to failure (clause 7.5.2.1(4)).

About loading procedures for the static load tests, Eurocode 7- Part 1 (CEN, 2004) mentions, in a note, the method suggested by ISSMGE (1985). The European standard for the static load tests in compression (prEN ISO 22477-1), which is in preparation (see above), is fully consistent and will apply when following Eurocode 7 provisions. With regard to dynamic load tests, Eurocode 7 – Part 1 adds that (clause 7.5.3 (1)): "Dynamic load tests may be used to estimate the compressive resistance provided an adequate site investigation has been carried out and the method has been calibrated against static load tests on the same type of pile, of similar length and cross-section, and in comparable soil conditions." Design of the bearing capacity with the French Standard for piles (AFNOR, 2012) The calculation methods implemented into the recent French standard for the design of piles following Eurocode 7 (AFNOR, 2012) are based on the results of pressuremeter tests (MPT) or of cone penetration tests (CPT). They follow the work initiated by Bustamante and Gianeselli (1981) and already used in the former French codes for piles (Fascicule 62-Titre V for civil engineering structures and DTU 13.2 for buildings) – see, for instance, for references in English, Bustamante and Frank (1999) and Bustamante et al. (2009). They are ‘direct’ methods in the sense that they correlate directly the result of the test (pl, the limit pressure for the MPT and qc, the cone resistance for the CPT) with the shaft resistance and base resistance of the pile. These correlations come from the results of numerous static tests on instrumented piles (pile databank of LCPC, the Central laboratory of the French highways), as advocated by Eurocode 7. For the preparation of the French standard (AFNOR, 2012) the databank has been revisited, not only because new data was available, but also in order to determine the ‘model’ factor γR;d which is explicitly mentioned in Eurocode 7 for the methods of assessment of the resistance of piles from ground test results (clause 7.6.2.3(2) for piles in compression and 7.6.3.3(2) for piles in tension). Figure 1 shows various distribution functions for the ratio Rc;cal/Rc;meas (calculated bearing capacity to measured bearing capacity) for the piles in compression using the various MPT methods. The data concern 155 piles of the so-called ‘Group 1’. ‘Group 1’ includes all piles, except coated driven steel and driven grouted H piles and micropiles of all categories (Baguelin et al. 2012; Burlon et al., 2014). From Figure 1 it can be seen that the value:

γR;d = 1.15 for the new PMT method (NF P94-262) covers 83% of the piles. This percentage is consistent with the former code for civil engineering structures (marked F62TV on Figure 1). This value has been selected for the piles in compression of ‘Group 1’ in the AFNOR (2012) standard. For more details on the calibration procedure for γR;d , see Burlon et al. (2014). Design Approach 2 of Eurocode 7 is used in France for piles for the ultimate limit states (ULS) in persistent and transient design situations (fundamental combinations), together with the value of the resistance factor recommended by Eurocode 7, that is γR = 1.1. Thus, for these design situations the ‘overall’ factor of safety on the resistance (bearing capacity) side is :

OFS = ξ . γR;d . γR where ξ is the correlation factor depending on the number of soil profiles (MPT or CPT) and their distance to the pile foundation. In the case that one soil profile is available at the location of the pile (or near the pile), the minimum value ξ = 1.08 is recommended in the AFNOR standard. Thus, for the MPT method and piles in compression:

OFS = 1.08 x 1.15 x 1.1 = 1.37

1,15 1,27

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155 essais

Figure 1. Distribution functions for the PMT methods, in the case of 155 piles of ‘Group 1’

(Baguelin et al., 2012) This value for the fundamental combinations is very near the value used in the previous French codes for piles (Fascicule 62-Titre V and DTU 13.2 for buildings). (It should not be forgotten that on the action side, the permanent unfavourable loads are increased by the factor γG;max = 1.35 and the leading unfavourable variable loads for buildings are increased by γQ = 1.5). Concluding remark Pile practice is in constant evolution for reasons of different nature. The codes and recommendations must be kept reasonably up-to-date. These documents must cover tests, execution and design of piles. Reference list AFNOR, 2012. Justification des ouvrages géotechniques - Normes d'application nationale de l'Eurocode 7 - Fondations profondes (in French - Justification of geotechnical work - National application standards for the implementation of Eurocode 7 - Deep foundations). Standard NF P 94-262, Association Française de Normalisation (French Association for Standardization), July 2012 (2nd reprint in January 2013), 206 p. Baguelin, F., Burlon, S., Bustamante, M., Frank, R. et Gianeselli, L., Habert, J. et Legrand, S, 2012. Justification de la portance des pieux avec la norme « fondations profondes » NF P 94-262 et le pressiomètre (in French). Journées Nationales de Géotechnique et de Géologie de l’Ingénieur, Bordeaux, pp. 564-577. Bond, A. and Harris, A., 2008. Decoding Eurocode 7 .London: Taylor & Francis, 598 p. Burlon, S., Frank, R., Baguelin, F., Habert J. and Legrand, S., 2014. Model factor for the bearing capacity of piles from pressuremeter test results. A Eurocode 7 approach. Submitted for publication to Géotechnique, London. Bustamante, M. & Gianeselli, L., 1981. Prévision de la capacité portante des pieux isolés sous charge verticale – Règles pressiométriques et pénétrométriques (in French). Bulletin des Laboratoires des Ponts et Chaussées, No. 113, pp. 83–108. Bustamante, M. & Frank., R., 1999. Current French design practice for axially loaded piles. Ground Engineering, March 1999, pp. 38–44. Bustamante, M., Gambin, M. and Gianeselli, L., 2009. Pile Design at Failure Using the Ménard Pressuremeter: an Up-Date,. IFCEE 2009. Proc. Int. Foundation Congress & Equipment Expo, Orlando, ASCE Geotechnical Publication, No. 186, pp. 127-134. CEN, 2004. Eurocode 7: Geotechnical design - Part 1: General rules. EN 1997-1:2004 (E), , November 2004, European Committee for Standardization: Brussels.

CEN, 2007. Eurocode 7: Geotechnical design - Part 2: Ground investigation and testing. EN1997-2:2007 (E), March 2007, European Committee for Standardization: Brussels. Frank, R., Bauduin, C., Driscoll, R., Kavvadas, M., Krebs Ovesen, N., Orr, T. and Schuppener, B., 2004. Designer's guide to EN 1997 Eurocode 7 – Geotechnical design, Thomas Telford, London, 216 p. Gilbert, C., 2014. Standards on Special geotechnical works : Two decades of European collaboration. Proceedings International Conference on Piling and Deep Foundations, DFI-EFFC, Stockholm , 21-23 May 2014. ISSMFE, 1985. Axial Pile Loading Test, Suggested Method. Subcommittee on Field and Laboratory Testing, ASTM Journal, June. Seters, A. van, 2014. Proceedings International Conference on Piling and Deep Foundations, DFI-EFFC, Stockholm , 21-23 May 2014.