44
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
constant CPT trace sections with
q
c
= 21±2 MPa, although this
was achieved at a shallower depth with the smaller Internal
Diameter (ID) membrane. Also shown is the
q
c
profile predicted
by Zhang et al 2013 that is discussed later.
Rimoy 2013 describes more recent experiments with the
same equipment, noting that axial capacities from multiple load
tests agree encouragingly well with predictions made with the
‘field-calibrated’ capacity approach outlined by Jardine et al
2005b, which gave good results for the Dunkerque field tests.
1200
1000
800
600
400
200
0
0 5 10 15 20 25
Penetration (mm)
200mm ID top membrane
50mm ID top membrane
Numerical simulation
q
c
(MPa)
Fig. 24. Measured and predicted
q
c
profiles with alternative CC top-
membranes: Jardine et al. 2013a and Zhang et al 2013
0.25
0.25
0.25
0.50
0.75
1.0
1.5 2.0
0.50
0 5 10 15 20
-30
-20
-10
0
10
20
30
40
50
r
/
R
h
/
R
0
1.0
2.0
3.0
4.0
5.0
6.0
4.8
0.75
1.0
1.5
1
1.5
2.0
3.0
1.0
4.0
6.0
8.3
0
5
-10
-5
0
5
10
10
r
/
R
h
/
R
0
2.0
4.0
6.0
8.0
10
Fig. 25. Contoured radial stresses around a penetrating conically tipped
pile (normalized by
q
c
and shown in %) as measured in laboratory CC
tests: Jardine et al. 2013b
Jardine et al 2013a, b report and interpret the measurements
made during installation, referring to these as the ‘Mini-ICP
data-set’. Pile penetration invoked extreme stress changes in all
three normal stress components and significant stress changes
out to r/R>33. Synthesising thousands of stress measurements
led to contour plots for the stress components including the
radial stress set given in Fig. 25 derived for ‘moving’ steady
penetration (σ΄
rm
) stages. The results are normalized for local
q
c
and plotted with cylindrical co-ordinates defined relative to the
pile tip. Normalised vertical distances (h/R) above are positive,
points below have negative h/R. Separate plots were derived for
‘stationary’ pause radial stresses (σ΄
rs
points) recorded when the
pile head was unloaded fully. Moving and stationary contour sets
were also reported for the vertical (σ΄
z
) and hoop (σ΄
θ
) stresses.
0
5
10
15
20
0.0
0.5
1.0
1.5
2.0
2.5
3.0
'
rs
/
q
c
: %
r
/
R
h/R=5.6
h/R=16~21
h/R=31.1
h/R=40.6
(a)
Fig. 26. Radial profiles of radial stresses measured around model pile
after installation in laboratory Calibration Chamber (normalized by
q
c
and shown in %): Jardine et al. 2013b
The contour plots indicate intense stress concentrations
emanating from the pile tip. Radial stress maxima exceeding
15%
q
c
were observed at h/R~0.5, r/R=2 during penetration,
while the ‘zero-load’ stationary values were 2 to 3 times smaller.
Yang et al 2010 describe how an active failure develops beneath
the advancing tip where, on average, σ΄
zm
/q
c
= 1, σ΄
rm
= σ΄
θm
=
K
A
σ΄
zm
and K
A
= tan
2
(45 + φ
'
/2). Close analysis of the ‘moving’
and stationary’ stresses measurements shows the greatest
divergence near the tip (-5 <h/R < 3) where substantial
differences extend to r/R = 10. Variation is mainly restricted to
the r/R < 2 region at higher levels on the shaft.
The most reliable observations of how stresses vary with r/R
(at set h/R values) were developed from the end-of-installation
measurements. The stationary σ΄
r
and σ΄
θ
profiles interpreted by
Jardine et al 2013b for four h/R values are presented in Figs. 26
and 27. Note that the final radial stresses develop maxima away
from the shaft, between 2 <r/R < 4; σ΄
θ
must vary steeply with
r/R to maintain equilibrium and give σ΄
θ
> σ΄
r
close to the shaft.
0
5
10
15
20
0
1
2
3
'
s
/
q
c
: %
r
/
R
h/R=5.6
h/R=16~21
h/R=31.1
h/R=40.6
(b)
Fig. 27. Radial profiles of hoop stresses around model pile after
installation, (normalized by
q
c
and shown in %): Jardine et al 2013b.
The above effective stress profiles, taken in combination with
the time-dependent behaviour discussed in Section 4, have the
