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Development of the UWA-05 Design Method for Open and Closed Ended
Driven Piles in Siliceous Sand

Conference Paper · October 2007

DOI: 10.1061/40902(221)12

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The UWA-05 method for prediction of axial capacity of driven piles in
sand
B. M. Lehane, J.A. Schneider and X. Xu
The University of Western Australia (UWA), Perth

ABSTRACT: This paper describes a new method for evaluating the axial capacity of driven piles in siliceous
sand using CPT qc data. The method is shown to provide better predictions than three other published CPT
based methods for a new extended database of static load tests. The design expressions incorporate the most
important features currently accepted as having a controlling influence on driven pile capacity at a fixed time
after installation (e.g. the effects of soil displacement, friction fatigue, sand-pile interface friction, dilation at
the shaft and loading direction) and are seen to reduce to a simplified form for typical (large diameter) off-
shore piles.

tail, although all assume a near-proportional re-

1 INTRODUCTION AND BACKGROUND
lationship between local shaft friction (τf) and qc
The authors, at the request of the American Petrole- and allow for the degradation of τf with distance
um Institute (API) piling sub-committee, recently above the pile tip (h) due to friction fatigue.
conducted a review of methods for the assessment of 3. The ICP-05 method indicated the lowest coeffi-
the axial capacity of driven offshore piles in sili- cient of variation (COV) for calculated to meas-
ceous sand. The review, which is described in detail ured capacities (Qc/Qm) of 0.32, when an equal
in Lehane et al. (2005a) and involved the develop- weighting is given to each pile test in the data-
ment of an extended database of static load tests, base. However, the relative performance of each
evaluated the existing API recommendations (API- method for various categories within the data-
00) and three Cone Penetration Test (CPT) based base is less clear. For example, NGI-04 predic-
methods namely: Fugro-04 (Fugro 2004), ICP-05 tions appear best for open-ended piles in com-
(Jardine et al. 2005) and NGI-04 (Clausen et al. pression while Fugro-04 and ICP-05 provide
2005). A new design method, referred to as UWA- comparable predictive accuracies for open-ended
05, emerged following the evaluation exercise and is piles in tension.
the described in this paper and in Lehane et al. 4. When account was taken of the relative reliabil-
(2005b). ity of the pile test data (using a carefully de-
The assessment of the predictive performance of signed weighting procedure), the methods listed
API-00, Fugro-04, ICP-05 and NGI-04 against the below for each category of pile lead to the low-
new UWA pile test database indicated the following est probability of failure:
trends (which are described in detail in Lehane et al.  API-00: closed-ended piles in compression
2005a):  Fugro-04: closed-ended piles in tension
1. All three CPT based design methods considered  ICP-05 & NGI-04: open-ended piles in com-
(Fugro-04, ICP-05 & NGI-04) had significantly pression
better predictive performance than the existing  ICP-05 & Fugro-04: open-ended piles in ten-
API recommendations, which were seen to lead sion
large under-predictions in dense sands and be- 5. API-00 gives the lowest probability of failure for
come progressively non-conservative as the pile closed-ended piles in compression partly be-
length (L) or aspect ratio (L/D) increased. cause the method generally under-predicts the
2. Despite the CPT based methods having a broad- capacity of the database piles to a significant de-
ly similar predictive performance against the gree. However, while the same average level of
new database of load tests, their formulations re- under-prediction also applies to API-00 predic-
lating the pile end bearing with the cone tip re- tions for closed-ended piles in tension, the esti-
sistance (qc) are notably different. Formulations mated probability of failure is larger than the
for shaft friction also differ significantly in de- three alternative CPT design methods.
6. The ICP-05 method displays a tendency to under- cal when using CPT data collected offshore,
predict pile base capacities (when assuming ca- which are often not continuous.
pacity solely from annular end bearing) and to be-  The values of qb0.1 for driven piles are less than
come potentially non-conservative for tension ca- q c because the displacement of 0.1D is insuffi-
pacity as the pile aspect ratio (L/D) increases. The cient to mobilise the ultimate value (of q c ).
Fugro-04 method indicates a tendency to under-  The findings of Randolph (2003), White & Bol-
predict compression capacities for long piles and ton (2005), and others, are consistent with the
to over-predict base capacities in loose sand. UWA-05 proposal to adopt a constant ratio of
qb0.1/ q c for driven closed-ended piles.
The examination of the three CPT based methods
coupled with a review of their various deficiencies The UWA-05 design equation for the end bearing of
and a careful examination of the new extended data- a closed-ended pile, with diameter D, is given as:
base of static load tests prompted the authors to pro-
pose the UWA-05 method presented here. This  2
Q b  q b 0.1 D where qb0.1/ q c = 0.6 (1)
method is believed to represent a significant im- 4
provement on Fugro-04, ICP-05 and NGI-04 meth-
ods. Particular comparisons are made with ICP-05, 2.1.2 Open-ended piles
which Lehane et al. (2005a) adjudged to have a  Salgado et al. (2002), Lehane & Gavin (2001,
marginally better predictive performance than the 2004), and others, have shown that a relatively
other two CPT based methods. consistent relationship between qb0.1 for a pipe
pile and the CPT qc value becomes apparent
2 THE UWA-05 DESIGN METHOD FOR PILES when the effects of sand displacement close to
IN SAND the tip during pile driving are accounted for. This
installation effect is best described by the incre-
2.1 End Bearing mental filling ratio (IFR) measured over the final
Factors that were considered in the development of stages of installation- and is referred to here as
the UWA-05 proposals for base capacity evaluation the final filling ratio (FFR). As the FFR ap-
of closed and open-ended piles are listed in the fol- proaches zero, qb0.1 approaches that of a closed-
lowing. These proposals are based on the analyses ended pile with the same outer diameter.
reported in Xu & Lehane (2005) and Xu et al.  The displacement induced in the sand in the vi-
(2005). The base capacity is defined as the pile end cinity of the base is most conveniently expressed
bearing resistance at a pile base movement of 10% in the terms of the effective area ratio Arb*, de-
of the pile diameter, qb0.1. fined in Equation 2c. This ratio depends on the
pile’s D/t (diameter to wall thickness) ratio and
2.1.1 Closed-ended piles the FFR value, varying from unity for a pile in-
 The strong direct relationship between the end stalled in a fully plugged mode to about 0.08 for a
bearing resistance of a closed-ended driven pile pile installed in coring mode with D/t of 50.
and the cone tip resistance, qc, has been recog-  Lehane & Randolph (2002), and others, have
nised for many years and arises because of the shown that, if the length of the soil plug is greater
similarity between their modes of penetration. than 5 internal pile diameters (5Di), the plug will
 Given the difference in size between a pile and a not fail under static loading, regardless of the pile
cone penetrometer, a correlation between qb0.1 diameter.
and qc requires use of an appropriate averaging  Experimental data and numerical analysis indi-
technique to deduce an average value of q c . Xu cate that the resistance that can develop on the tip
& Lehane (2005) show that, for many stratigra- annulus at a base movement of 0.1D varies be-
phies encountered in practice, q c may be taken tween about 0.6 and 1.0 times the CPT qc value
as the average qc value taken in the zone 1.5 pile (e.g. Bruno 1999, Salgado et al. 2002, Lehane &
diameters (D) above and below the pile tip. Gavin 2001, Paik et al 2003, Jardine et al. 2005).
 Xu & Lehane (2005), however, also show that  Lehane & Randolph (2002) suggest that the base
when qc varies significantly in the vicinity of the resistance provided by the soil plug for a fully
pile tip (i.e. within a number of diameters), the coring pile (with FFR =1) is approximately
Dutch averaging technique (Van Mierlo & equivalent to that of a bored pile.
Koppejan 1952, Schmertmann 1978) provides the  Recommended values of qb0.1/qc for bored piles
most consistent relationship for end bearing and range from 0.15 to 0.23 (Bustamante &
should be employed to calculate q c . Gianeselli 1982, Ghionna et al. 1993). These rati-
 A simplified (and conservative) means of deter- os are not dependent on the pile diameter.
mination of the Dutch q c value is provided in  The value of q c should be evaluated in the same
Lehane et al (2005b), which may be more practi- way as that employed for closed-ended piles, but
 using an effective diameter (D*) related to the ef- is likely to vary with the effective area ratio
fective area ratio, Arb* i.e. D* = D × Arb*0.5. raised to a power of between 0.30 and 0.40.
 There are relatively few documented case histo-  The incremental filling ratio (IFR) is a measure
ries that report the incremental or final filling ra- of soil displacement near the tip of a pipe pile and
tios. In the absence of FFR measurements, a depends on a number of different parameters, in-
rough estimate of the likely FFR may be obtained cluding soil layering, pile inner diameter, pile
using equation 2d (see Xu et al. 2005). wall thickness, plug densification or dilation, and
The UWA-05 proposal for end bearing of driven installation method. For the (limited) database of
pipe piles is provided in Equation (2). This proposal IFRs reported, the mean IFR over the final 20D
is developed in Xu et al. (2005) and shown to com- of penetration (where most friction is generated)
pare favourably with the existing database of base can be reasonably approximated using Equation
capacity measurements for open-ended piles. (3e) for relatively uniform dense to very dense
sands in the database.
 2  After displacement of the sand near the tip in a
Q b  q b 0.1 D (2a)
4 given soil horizon and as the tip moves deeper,
the radial stress acting on the pile shaft (and
*
q b 0.1 / q c  0.15  0.45A rb (2b) hence the available τf value) in that horizon re-
duces. This phenomenon, known as friction fa-
 Di 2  tigue, is now an accepted feature of displacement
 1  FFR  2 
*
A rb (2c) pile behaviour (e.g. see Randolph 2003).
D   The rate of radial stress and τf reduction with
height above the tip (h) depends largely on the
  D ( m)  0.2  magnitude and type of cycles imposed by the in-
FFR  min 1,  i   (2d) stallation method. White & Lehane (2004) show
  1.5m   that the rate of decay is stronger for piles experi-
where Di is the inner pile diameter. encing hard driving and much lower for jacked
piles, which are typically installed with a relative-
2.2 Shaft Friction ly low number of (one-way) installation cycles.
 White & Lehane (2004), and others, also show
Factors that were considered in the development of that the rate of degradation with h is greater at
the UWA-05 method for shaft friction are discussed higher levels of radial stiffness (4G/D) and there-
in Schneider & Lehane (2005) and Lehane et al. fore τf at a fixed h value (i.e. after a specific
(2005a). These are now summarised as follows: number of installation cycles) in a sand with the
 Local shaft friction (τf) shows a strong correlation same operational shear modulus (G) reduces as D
with the cone tip resistance (qc). This correlation, increases.
which has been observed directly in instrumented  The foregoing, plus the tendency for hammer se-
field tests has been employed successfully in well lection to be such that the number of hammer
known design methods, such as that proposed by blows is broadly proportional to the pile slender-
Bustamante & Gianiselli (1982). ness ratio (L/D), suggest that τf may be tentative-
 The shaft friction that can develop on a displace- ly considered a function of h/D. This approxima-
ment pile is related to the degree of soil dis- tion is supported by field measurements such as
placement imparted during pile installation. The those provided in Lehane et al (2005a), and is al-
higher capacity developed by the new generation so compatible with the occurrence of a ‘critical
of screw piles compared to that of a bored and depth’ at an embedment related to a fixed multi-
continuous flight auger piles is just one example ple of the pile diameter (such as 20D proposed by
of this effect. Vesic 1970 and a number of workers). The same
 The degree of displacement imparted to any giv- approximation is employed by the ICP-05 and
en soil horizon is related to the displacement ex- Fugro-04 design methods.
perienced by that horizon when it was located in  Based on the former point, the ICP-05 method
the vicinity of the tip. This level of displacement proposes that τf varies in proportion to (h/D)-c,
can conveniently be expressed for both closed where c = 0.38. However, given that this value of
and open-ended piles in terms of an ‘effective ar- c was estimated on the basis of field tests with
ea ratio’, Ars*, which is unity for a closed ended jacked piles (Lehane 1992 and Chow 1997)
pile and, for a pipe pile, includes displacement where the type and number of cycles imposed is
due to the pile material itself and the additional less severe than is typical of driven piles, a higher
displacement imparted when the pile is partially value of c is considered more appropriate for off-
plugging or fully plugged during driving. White shore pile. Strong indirect evidence in support of
et al. (2005) use a cavity expansion analogy to this observation is also apparent in Lehane et al
deduce that the equalized lateral effective stress (2005a), which shows that the Fugro-04, ICP-05
 and NGI-04 progressively under-predict the shaft f
capacity of jacked piles as the pile length increas-  f  ' rf tan cv  ' rc  ' rd  tan cv (3b)
fc
es
 The radial effective stress acting on a driven pile 0.5
increases during pile axial loading and its magni-
tude (when τf is mobilised and dilation has
' rc  0.03  q c A rs   * 0.3   h 
 max  D ,2  (3c)
  
ceased) increases as the pile diameter reduces, the
sand shear stiffness around the pile shaft increas-
es and the radial movement during shear (dila- D 2
A rs  1  IFR  i2 
*
(3d)
tion) of the sand at the shaft interface increases. D 
These increases are not significant for offshore
piles (with large D) but need to be considered   D i ( m)  0.2 
when extrapolating from load test data for small IFR mean  min 1,    (3e)
diameter piles in a database. The recommenda-   1.5m  
tions of the ICP-05 method are considered rea-
sonable for assessment of the increase in radial ' rd  4G  r D (3f)
stress (∆σ'rd), but with a modified expression for
the shear stiffness derived from the CPT data. where
 τf varies in proportion to tan δcv (where δcv is the cv = constant volume interface friction angle
constant volume interface friction angle between 'rf = radial effective stress at failure
the sand and pile); this δcv value, which should be 'rc = radial effective stress after installation and
measured routinely, increases as the roughness equalization
normalized by the mean effective particle size 'rd = change in radial stress due to loading stress
(D50) increases. Verification of the dependence of path (dilation)
τf on tan δcv has been provided by Lehane et al. f / fc = 1 for compression and 0.75 for tension
(1993), Chow (1997), and others. In the absence G/qc = 185·qc1N-0.75 with qc1N=(qc/pa)/('v0/pa)0.5
of specific laboratory measurements of δcv. pa = a reference stress equal to 100 kPa
UWA-05 recommends the trend shown on Figure 'v0 = in situ vertical effective stress
1, which is the same as that employed by ICP-05 r = dilation (assumed for analyses=0.02mm, as
but with an upper limit on tanδcv value of 0.55 for ICP-05)
(due to the potential for changes in surface 32
roughness during pile installation). Employed for
database evaluation
 The shaft friction that can develop on a pile in 30
tension is smaller than that which can be mobi-
Interface Friction Angel,  cv

tan  < 0.55

lised by a pile loaded in compression for the rea- 28
UWA-05

sons described by Lehane et al. (1993), de Nicola recommendation

& Randolph (1993) and Jardine et al. (2005).

 Because of the shortage of high quality measure- 26

ments of τf very close to the tip of a driven pile

and the variable and inconsistent trends shown by 24
the available measurements, one simplifying op-
tion is to assume τf is constant over the lower two 22
diameter length of the pile shaft for both closed
and open-ended piles in tension and compression. 20
 Shaft capacity increases with time as shown by 0.01 0.1 1 10
Axelsson (1998), Jardine et al. (2005a), and oth- Median Grain Size, D50 (mm)
ers. Lehane et al (2005a) show, however, that rate
Figure 1. cv variation with D50 (modified from ICP-05 guide-
of increase over the period 3 days to 50 days is lines)
not statistically significant for the UWA database
of load tests. A design time of 10 to 20 days is
considered appropriate for shaft friction calculat- 3 PREDICTIVE PERFORMANCE OF UWA-05
ed using UWA-05.
The UWA-05 design equations for shaft capacity The UWA database of static loads tests, as discussed
of driven piles arose from the foregoing considera- in Lehane et al (2005a & b), was employed to assess
tions and are expressed as follows: the predictive performance of the proposed UWA-05
Q s  D   f dz (3a) method. The predictions described employed equa-
tions (1), (2) and (3) with the following additional
considerations:
 Measured interface friction angles, when availa- en that the incremental filling ratio (IFR) is not
ble, were adopted. Figure 1 was used in the ab- commonly measured in practice, the sensitivity of
sence of measured δcv values. the predictive performance to the IFR parameter
 When the incremental filling ratio (IFR) was rec- employed was re-examined and a summary of this
orded, Arb* was assessed using the mean IFR val- exercise is provided in Table 1.
ue measured over the final 3D of pile penetration It is clear from Table 1 that the estimation of IFR
while the value of Ars* was assessed from the using the empirical equations 2d & 3e, rather than
mean IFR value recorded over the final 20D of direct use of the measured IFRs to deduce Ar* val-
penetration. In the absence of IFR data, Arb* and ues, has only a minimal impact on the COV values
Ars* were evaluated using Equations 2d & 3e. for Qc/Qm. It may also be inferred that the assump-
The database included 74 load tests at sites where tion in UWA-05 of a fully coring pile (i.e. IFR=1)
CPT qc data were measured. Pile test data at sites for the database piles (most of which had diameters
containing micaceous, calcareous and residual sands less than 800mm) will lead, on average, to a 20%
were excluded from consideration – as were sites for under-prediction of capacity. Such an under-
which only Standard Penetration Test data were prediction is in keeping with observed levels of par-
available. The database included substantially more tial plugging of (smaller diameter) database piles
pile tests than used for verification of the Fugro-04, and suggests that other design methods, such as ICP-
ICP-05 and NGI-04 design methods and was sub- 05, which may provide a good fit to the existing da-
divided into the following four categories: tabase of load tests, but do not include an appropri-
ate soil displacement term (such as Ar*), will over-
(a) Closed-ended piles tested in compression predict the capacity of full scale offshore piles.
(b) Closed-ended piles tested in tension
(c) Open-ended piles tested in compression Table 1: Sensitivity of pipe pile capacity to Ar* (Arb* and Ars*)
(d) Open-ended piles tested in tension Method for calculation of Ar* Mean Qc/Qm
COV for
Qc/Qm
A detailed presentation and discussion of this statis- Open-ended piles in compression
tical analysis, which was conducted for API-00, Using Equations 2d & 3e for all tests 0.99 0.23
Fugro-04, ICP-05 and NGI-04, as well as for UWA- Assuming IFR= 1 0.81 0.24
05 is presented in Lehane et al. (2005a & b) and may Using measured IFR when available 0.98 0.19
be briefly summarized as follows: Open-ended piles in tension
Using Equations 2d & 3e for all tests 0.97 0.26
(i) For the database taken as a whole (i.e. including Assuming IFR=1 0.77 0.22
all pile categories), the UWA-05 method pre- Using measured IFR when available 0.91 0.23
dicts a mean ratio of calculated to measured ca-
pacity (Qc/Qm) of 0.97 and the lowest overall
coefficient of variation (COV) for this ratio of 4 PREDICTIONS FOR OFFSHORE PILES
0.29; this compares well with the respective
COVs of 0.32, 0.38, 0.43 and 0.6 for ICP-05, The UWA-05 method simplifies to the following
Fugro-04, NGI-04 and API-00. form for full scale offshore piles, as IFR=1 and the
(ii) The UWA-05 method has the lowest COV for dilation term (∆σ’rd) can be ignored.
Qc/Qm of all five methods for each of the four

pile test categories (except for closed-ended Q comp  Q b  Q s  q b 0.1 D 2  D   f dz (4a)
piles in compression where UWA-05 and ICP- 4
05 have the same COV for Qc/Qm).
(iii) The COV of 0.19 for Qc/Qm of the UWA-05 Q tens  0.75  D   f dz (4b)
method for open-ended piles in compression is
significantly lower than the corresponding COV q b 0.1  q c  0.15  0.45A r  (4c)
of 0.25 of ICP-05.
(iv) UWA-05 shows no apparent bias of Qc/Qm with 0.5
pile length (L), pile diameter (D), pile aspect ra-   h 
 f  0.03  q c A  max  ,2 
0.3
r tan  cv (4d)
tio (L/D) and average sand relative density.   D 
One of the factors giving rise to the superior per-
formance of the UWA-05 method for pipe piles is  Di 2 
the inclusion of the effective area ratio terms in the A r  1   2  (4e)
expressions for base and shaft capacities of open D 
ended piles. This is not surprising given the
acknowledged importance of soil displacement on Lehane et al. (2005b) examined the implications
capacity and the fact that many of the database piles of equation (4) and assessed its performance against
showed evidence of partial plugging. However, giv- existing API recommendations and ICP-05 (the best
performing of the three CPT based methods consid- Jardine, R.J., Chow, F.C., Overy, R., and Standing, J. 2005.
ered). This examination indicated that equation (4) ICP design methods for driven piles in sands and clays.
Thomas Telford, London.
provides a more conservative extrapolation than Jardine, R.J., Standing, J.R., & Chow, F.C. 2005a. Field re-
ICP-05 for shaft capacity from the existing database search into the effects of time on the shaft capacity of piles
(of relatively small diameter piles – with a mean D driven in sand. Proc., ISFOG, Perth.
of about 0.7m) to typical offshore piles used in prac- Lehane, B.M., Jardine, R.J., Bond, A.J., & Frank, R. 1993.
tice. Equation (4) also predicts higher base capaci- Mechanisms of shaft friction in sand from instrumented
ties than ICP-05 because of its assumption that a pile pile tests, J. of Geotech. Engrg., ASCE, 119 (1):19 – 35.
Lehane, B. M. & Gavin, K. G. 2001. Base resistance of jacked
plug with a length greater than 5 diameters will not pipe piles in sand. J. of Geotech. and Geoenv. Engrg,
fail under static loading. ASCE 127(6): 473-480.
It is also noteworthy that Equation (4) tends to Lehane B.M. & Gavin K. 2004. (Discussion). Determination of
provide lower capacities than API-00 in loose sands, bearing capacity of open-ended piles in sand. J. Geotech. &
but higher capacities for dense sands in compres- Geoenv. Engrg. ASCE 130 (6): 656-658.
Lehane, B. M. & Randolph, M. F. 2002. Evaluation of a mini-
sion. API-00 and UWA-05 predictions for tension mum base resistance for driven pipe piles in siliceous sand.
capacity in dense sands are broadly similar for pile J. of Geotech. and Geoenv. Engrg., ASCE 128(3): 198-205.
lengths in excess of 20m. However, the UWA-05 Lehane, B. M. 1992. Experimental investigations of pile be-
method, unlike API-00, does not show any predic- haviour using instrumented field piles. PhD thesis, Univ. of
tion bias with L, D, L/D and Dr. London (Imperial College).
Lehane, B.M., Schneider, J.A., and Xu, X. 2005a. Evaluation
of design methods for displacement piles in sand. UWA
Report, GEO: 05341.1.
5 CONCLUSIONS Lehane, B.M., Schneider, J.A., and Xu, X. 2005b. CPT based
design of driven piles in sand for offshore structures. UWA
This paper has shown that the UWA-05 method: Report, GEO: 05345.
Paik, K., Salgado, R., Lee, J. & Kim, B. 2003, Behavior of
open- and closed-ended piles driven into sands. J. of Ge-
(i) is a significant improvement on existing API otech. and Geoenv. Engrg., ASCE. 129(4): 296-306.
recommendations; Randolph, M. F. 2003. Science and empiricism in pile founda-
(ii) provides better predictions for a new extended tion design. Geotechnique 53(10): 847-875.
database of load tests than the ICP-05, Fugro- Salgado, R. Lee, J. And Kim, K. 2002. Load tests on pipe piles
04 and NGI-04 CPT based design approaches; for development of CPT-based design method. Final report,
FHWA/IN/JTRP-2002/4.
(iii) employs soundly based formulations that draw Schneider, J.A. & Lehane, B.M. (2005). Correlations for shaft
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