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 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

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).

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)

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)

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)

EC 7-1: Recommended values for the x - factors for Rk from n – static load tests French practice (Fascicule 62-V) : x ≤1.2 x for n = 1 2 3 4  5 x1 1.40 1.30 1.20 1.10 1.00 x2 1.05

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

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)

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 gs = gst = 1.4 on Qcreep (F 62-V)

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 ?

Thank you for your attention !