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The French standard for the application of Eurocode 7 to deep foundations

Learn about the application of Eurocode 7 to deep foundations, including bearing capacity, displacement, and innovative design approaches. Explore the importance of static load tests and structure serviceability assessments.

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The French standard for the application of Eurocode 7 to deep foundations

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  1. The French standard for the application of Eurocode 7 to deep foundations Roger Frank, Ecole des ponts Sébastien Burlon, IFSTTAR 1

  2. Outline Introduction – Aspects of pile design following Eurocode 7 (EN 1997-1) 1 – Table of contents of NF P 94-262 (July 2012) 2 – Bearing capacity from CPT (assessment of ‘model factors’ gR;d ) 3 – Displacement under axial and transverse loads (PMT "t-z" and « "p-y" methods) Conclusions/Prospective

  3. Bearing capacity of piles according to Eurocode 7(compressive/tensile « resistance ») The design shall be based on : a)on the results of static load tests b) empirical or analytical calculation methods validated by static load tests in comparable situations  introduction of ‘model factor’ γRd c) results of dynamic load tests whose validity has been demonstrated by static load tests in comparable situations d)the observed performance of a comparable pile foundation (to be supported by site investigation and ground testing).

  4. * importance of static pile load tests * an innovative approach to pile capacity taking account of number of load tests or number of soil profiles (through the x values) * importance of assessing serviceability of structures through displacement calculation Designing pile foundations with Eurocode 7 :

  5. French standard for the Application of Eurocode 7 july 2012

  6. NF P 94-262 : Table of contents 15 sections and 19 annexes (98 pages +108 pages) Main sections: • combinations of actions and action effects • ultimate compressive resistance (bearing capacity) • ultimate tensile resistance • resistance to transverse loadings • structural resistance (concrete and steel properties for piles) • overall stability • verifications of serviceability limit states 6

  7. 2. Bearing capacity from CPT (assessment of ‘model factors’ gR;d ) 7

  8. (Bustamante et al. , IFCEE '09, 2009) 8

  9. The database of IFSTTAR (LCPC) 9

  10. 10

  11. 11

  12. Piles distribution by class and soil type for CPT profiles 12

  13. CPT rules : base resistance Values of kc (for De/B > 5) 13

  14. CPT rules: shaft resistance qs =a f sol and qs ≤ qsmax 0,2 ≤a≤ 2,25 and qsmaxvary according to soil type and pile category 14

  15. 0,2 ≤a≤ 2,25 vary according to soil type and pile category 15

  16. qsmax varie selon la classe de sol et la catégorie de pieu qsmaxvary according to soil type and pile category (identical to pressuremeter) 16

  17. CPT rules – 31 tests(no injected piles; no chalk) Moy : 0.86Mediane: 0.80COV: 0.34Quantile for 1.18: 85 % γRd1 = 1.18 17

  18. Design value of the compressive (or tensile) capacity from ground test results‘Model pile’ procedure : Rd = Rk/gR = Rmod/(gR;d1*  *gR) with  a correlation factor ‘Alternative’ procedure (‘ground model’) : Rd = Rk/gR = Rmod/(gR;d1*gR;d2*gR) with gR;d2 = 1,1 Resistance factor (Design Approach 2 - all cases, in compression) : gR = 1,1 18

  19. Model coefficient gRd;1 for CPT method(and gRd;2 = 1,0 or 1,1)

  20. 3. Displacement under axial loads(PMT "t-z" method ) t-z curves from Ménard pressuremeter modulus EM(Frank & Zhao, 1982) for fine grained soils : kt = 2.0 EM/B and kq = 11.0 EM/B for granular soils : kt = 0.8 EM/B and kq = 4.8 EM/B

  21. 1st example : cased screw pile in Ypresian clay (Belgium) 21

  22. with Kf = 2ESM 18 18 EsM = EM --------------------------------------------- or EM -------------------------- 4(2,65 B/Bo)a Bo/B + 3a4(2,65)a + 3a EsM = Ménard subgrade reaction modulus Behaviour under transverse loads ("p-y"method ) Examples of "p-y" curves from PMT results Short duration Long duration

  23. Pile of Provins (1974) 23 (Bigot, Bourges and Frank, 1982)

  24. Conclusions/Summary New PMT rules for piles have been elaborated in France (recent standard for piles, compatible with Eurocode 7, 2012). They have been fully calibrated against the databank of more than 170 full scale static load tests on instrumented piles. These full scale tests were mainly performed at the occasion of real projects/case studies. Corresponding PMT rules have also been calibrated (with more reliability!). The important role of displacements of foundations of structures is fully recognised (more than the safety with regard to soil failure ?…) 24

  25. Thankyou for your attention ! Acknowledgments: 25

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