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Axial resistance of micropiles : from French to Eurocode design

Axial resistance of micropiles : from French to Eurocode design. Roger Frank CERMES (ENPC-LCPC), Paris, France. Eurocode 7-1 : check of axial capacity of pile foundations. ULS compressive or tensile resistance failure of a single pile ULS of the pile foundation as a whole

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Axial resistance of micropiles : from French to Eurocode design

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  1. Axial resistance of micropiles : from French to Eurocode design Roger Frank CERMES (ENPC-LCPC), Paris, France

  2. Eurocode 7-1 : check of axial capacity of pile foundations • ULS compressive or tensile resistance failure of a single pile • ULS of the pile foundation as a whole • ULS of collapse or severe damage to a supported structure by excessive displacement or differential displacements of the pile foundation • SLS in supported structure by displacements of the piles

  3. Axial resistance of piles/micropiles • 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).

  4. Basic relations for axial resistance The basic relations of Eurocode 7-1 are : Rk = Rm/x (1) Rd = Rk/gt(or Rd = Rbk/gb + Rsk/gs) (2) Or Rd = Rk/gst On the other hand : Fd = gFF (3)

  5. The basic condition for all ULS is : Fd(ULS)  Rd (4) Eqs (1) to (4) lead to : Fd Rm/ gF.gt.x = Rm/FS (5)

  6. Eurocode 7- 1 : Characteristic resistance from static load tests Rk = Min { Rm,mean/1 ; Rm,min / 2 } where Rm : measured resistance(s) with x = x1 on the mean, or x = x2 on minimum value function of the number of pile test(s) (n)

  7. EC 7-1: Recommended values for the x - factors for Rk from n – static load testsFrench practice (Fascicule 62-V) : x ≤1.2

  8. Factors on actions (EC 7-1 and F 62-V) • ULS, permanent and transient situations : F = 1.35 to 1.5 • ULS, accidental situations : F = 1.0 • SLS : F = 1.0

  9. Factors for micropile side resistance : Eurocode 7-1 and Fascicule 62-V • ULS persistent and transient situations s = 1.1 and st= 1.15 (approach 2 of EC 7-1) gs = gst = 1.4 (F 62-V) • ULS accidental situations s =st = 1.0 (EC 7-1) gs = gst = 1.2 (F 62-V)

  10. Factors for micropile side resistance : Eurocode 7-1 and Fascicule 62-V • SLS characteristic combinations check the displacements(EC 7-1) gs = gst = 1.1 on Qcreep(F 62-V) • SLS quasi-permanent combinations check the displacements(EC 7-1) gs = gst = 1.4 on Qcreep(F 62-V)

  11. Conclusion • The main challenge is the prediction of displacements, whether for ULS or for SLS … • Which model(s) to use : t-z approach or others ? • How to collect the data ? • Which are the tolerance criteria ?

  12. Thank you for your attention !

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