Transcript Design of micropiles : from French to European practice

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)
Or
Rd = Rk/gt (or
Rd = Rk/gst
Rd = Rbk/gb + Rsk/gs)
On the other hand : Fd = gFF
(2)
(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/x1 ; Rm,min / x2 }
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
x for n =
x1
x2
1
1.40
1.40
2
1.30
1.20
3
1.20
1.05
4
1.10
1.00
5
1.00
1.00
French practice (Fascicule 62-V) : x ≤1.2
Factors on actions (EC 7-1 and F 62-V)



ULS, permanent and transient
situations :
gF = 1.35 to 1.5
ULS, accidental situations :
gF = 1.0
SLS :
gF = 1.0
Factors for micropile side resistance :
Eurocode 7-1 and Fascicule 62-V


ULS persistent and transient situations
gs = 1.1 and gst= 1.15 (approach 2 of EC 7-1)
gs = gst = 1.4
(F 62-V)
ULS accidental situations
gs = gst = 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
check the displacements
(EC 7-1)
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
!