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

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 Eurocode 7-1 : check of axial capacity of pile foundations

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). Axial resistance of piles/micropiles

Basic relations for axial resistance The basic relations of Eurocode 7-1 are : R k = R m /  (1) R d = R k /  t (orR d = R bk /  b + R sk /  s ) (2) Or R d = R k /  st On the other hand : F d =  F F (3)

The basic condition for all ULS is : F d (ULS)  R d (4) Eqs (1) to (4) lead to : F d  R m /  F.  t.  = R m /FS (5)

Eurocode 7- 1 : Characteristic resistance from static load tests R k = Min { R m,mean /  1 ; R m,min /  2 } where R m : measured resistance(s) with  =  1 on the mean, or  =  2 on minimum value function of the number of pile test(s) (n)

EC 7-1: Recommended values for the  - factors for R k from n – static load tests French practice (Fascicule 62-V) :  ≤1.2  for n =1234  5 1 2

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

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)  s =  st = 1.4 (F 62-V) ULS accidental situations  s =  st = 1.0 (EC 7-1)  s =  st = 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)  s =  st = 1.1 on Q creep (F 62-V) SLS quasi-permanent combinations check the displacements (EC 7-1)  s =  st = 1.4 on Q creep (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 !