The site is located in Noosa Heads, Australia along Hastings St near a popular surf beach. 600mm diameter cast in place concrete piles were installed to a depth of 10m within loose to moderately dense coastal sand. Pile 68, which consumed over twice the design volume of concrete, was selected for static and dynamic testing. The static test results showed good correlation with the dynamic test up to a load of around 1700kN, but measurements above this load are considered inaccurate. Dynamic testing provided an excellent prediction of load-displacement behavior for the non-uniform pile, demonstrating the effectiveness of dynamic testing even when pile conditions differ from design.

1. 1 THE SITE
The site is on Hastings St, which is the commer-
cial/tourist centre of Noosa Heads in Queensland,
Australia. This is located only a few metres behind
a popular surf beach and is immediately adjacent to
a tidal inlet and small river. A geotechnical investi-
gation of the site had been conducted and 4 borehole
logs were provided that described subsoil conditions.
The logs suggest that the site is underlain by coastal
sand dune or “beach sand” material to a depth of
about 10m and this sand is underlain by very stiff to
hard clays with SPT results generally 35 but some as
low as 18. The sand is loose to moderately dense
with standard penetration test results generally in the
range 10 to 20 but with some higher and some lower
measurements. The SPT results in the sand did not
necessarily increase steadily with depth.
2 THE PILES
The foundation contract was let as a design and con-
struct package and the contractor adopted 600mm
nominal diameter “cfa” cast in place concrete piles
founded at a depth of about 10m (ie entirely within
the near surface sand with the toe being influenced
by the underlying hard clays). These piles were
constructed using a continuous flight auger (cfa) that
is drilled into the ground to a pre-selected level or
depth and then a cement grout or, as in this case,
high slump concrete is injected down the hollow
core of the auger as the auger is withdrawn without
rotation. The rig used on this project allowed for
monitoring of concrete volume and pressure
throughout construction of each pile. This permits
the pile constructor to assess whether the pile is
“consuming” more or less concrete than would be
expected for the nominal shaft diameter. When the
pile concreting is completed a reinforcing cage is
lowered with vibration into the high slump concrete.
The piling contractor adopted a high “geotech-
nical reduction factor” (ie low factor of safety) in the
design and in accordance with the Australian Piling
Code (see references) it was necessary to demon-
strate the load vs resistance behaviour of the piles.
He decided to adopt a single static load test and 4
high strain dynamic tests. One of the dynamic tests
was conducted on the static test pile to establish that
the dynamic testing would provide a good prediction
of a static load test.
Many of the piles for this project “consumed”
more concrete than would be expected for the nomi-
nal shaft diameter but the greatest “over-
consumption” was during construction of pile 68 and
this was selected for both static and dynamic testing.
The over-consumption on this pile was 105%, ie
Case study on the application of high strain dynamic pile testing to non-
uniform bored piles
J.G.Cannon
Independent Geoscience Pty Ltd, Melbourne, Australia
ABSTRACT: Dynamic pile testing is used frequently to prove the performance of driven pre-formed piles
in Australia. It is either specified by the designer or is offered as an alternative to conventional static testing
by piling contractors. However, it’s use on cast in place piles is much less frequent. This paper describes a
project at Noosa Heads in Queensland, Australia where an excellent “Grade A” correlation has demonstrated
that dynamic testing can provide a good prediction of the load vs displacement behaviour of cast in place piles
even when the pile shaft is not as designed.
The static test pile had the highest over-consumption of concrete at the site, with more than 2 times the
design quantity of concrete used during construction. A non-uniform shaft is known to make dynamic testing
more difficult and probably less accurate. Nevertheless a very good correlation was obtained between the
static test and the dynamic test results for both overall mobilized resistance and the stiffness response of the
pile.
The static test included measurements that demonstrate potential problems with static testing and these
will also be discussed.

2. more than 2 times the required volume of concrete
was used during construction. The contractor’s
equipment provided for measuring pressure and vol-
ume throughout construction of the pile so the pile
profile could be estimated. The contractors record
for pile 68 is shown in Figure 1. Most of the extra
concrete consumption is shown as a cone between 5
and 10m depth.
3 STATIC PILE TESTING
A static load test had been conducted on pile 68
prior to the dynamic pile testing. The contractor was
careful to avoid the dynamic testing consultant be-
coming aware of the static test results before the dy-
namic test results were reported. The static test was
conducted with several cycles in accordance with the
Australian Piling Code. Applied load was measured
using the jack pressure only. There are shortcom-
ings to this system that are described below. Dis-
placement was measured using 3 dial gauges. A
check of pile displacement was also taken using a
level survey. Load was applied by jacking against a
reaction beam and displacement of this beam was
also measured by level survey.
4 DYNAMIC PILE TESTING
The test piles were cast above ground level inside a
steel sleeve of about 4mm wall thickness and about
the same diameter as the pile for about 2.5 pile di-
ameters above the surrounding ground. This was
done at the same time as casting the pile or as soon
as possible after casting the pile in order to keep the
concrete for the extension of the same strength and
age as the remainder of the shaft. After the concrete
had hardened the bottom half of the steel sleeve was
removed. This leaves a substantial steel collar at the
top to reinforce the pile top during impacts of a drop
weight and allows the test equipment to be attached
at a level where there is a regular smooth surface
with no additional impedance that might interfere
with strain measurements. The location of the test
gauges had a diameter close to that of the pile shaft
and had similar reinforcing.
The Author uses the PAK model Pile Driving
Analyzer from Pile Dynamics Inc. together with the
associated CAPWAP signal matching software. The
method and current “state-of-the-art” has been de-
scribed in Goble et al (1996). The option to test
with 4 strain gauges was not adopted for piles of this
size.
Figure 1 - Construction record for dynamic/static test pile

3. The contractor supplied a “Hydroquip” HQ5 hy-
draulic piling hammer to strike the piles. Some re-
building of the hammer’s hydraulic valving had been
conducted to increase energy transfer efficiency.
Highest energy transfer efficiency during this testing
was 76%, which we consider to be high for a hy-
draulic hammer with a 5tonne ram striking a solid
concrete pile of this diameter.
Testing generally commenced with one or two
small blows (0.5m stroke) to ensure hammer align-
ment was satisfactory and then two or three blows of
high energy (1.2m stroke) were applied to gather test
data for later analysis with CAPWAP.
During CAPWAP analysis the pile was modeled
using the construction record but some additional
enlargement of the shaft was required near the top.
The Author considers the additional pressure created
by the shaft extension after the contractors monitor-
ing record was completed justifies this. The model
pile volume in the CAPWAP model was very close
indeed to the recorded volume of 205% of the nomi-
nal design
5 RESULTS
The static results are summarized in Figure 2,
below together with the CAPWAP load vs deflection
prediction plotted on the same axes.
It can be seen that in the static test when the pile
reaches a displacement of slightly less than 15mm
the inferred load increases but there is no corre-
sponding deflection of the pile. The Author consid-
ers that this is impossible and that there must have
been an error in the test measurements. The most
likely error was that the jack reached the end of its
travel or jammed such that although there was an in-
crease in jack pressure and hence inferred load on
the pile, in reality load did not increase and the pile
consequently did not deflect. The contractor’s per-
sonnel that conducted the test claim this was not the
case and consider that the jack did not reach the end
of it’s travel. However the measurements of the re-
action beam, which was also deflecting elastically,
show the same behaviour, with almost no deflection
during the last load application cycle. This is shown
in figure 3. The Author considers that the maximum
load applied to the pile did not exceed 1700kN.
As the static test was conducted on this pile prior
to the dynamic test it is relevant to plot the dynamic
test as an additional cycle to the static test. The re-
sults of the other tests at this site show a lower
“break-point” in the load vs deflection behaviour
and the Author considers this to be related to the
loading history of the piles. The “cfa” construction
is a non-displacement construction method. Owing
to the stress relief that occurs during construction it
would appear that these piles deflect more during
initial loading. Subsequent loading cycles appear to
behave with increased stiffness up to the point of
previous maximum loading. This behaviour has also
been noted by the Author at other projects with simi-
lar piles in sand ground conditions. If deflection is a
critical acceptance criteria for this pile type in sand
ground conditions then it may well be necessary to
“preload” the piles by “driving” them after construc-
tion.
If the maximum applied load during the static
load test was 1700kN this correlates well with the
“break point’ at about 1800kN in the CAPWAP load
vs deflection prediction for this pile. The
unload/reload stiffness shown in each of the load cy-
cles of the static test is also of interest as this corre-
lates quite well with the initial loading stiffness
shown in the dynamic test results.
The stiffness of the static test on initial loading
during each of the cycles also correlates reasonably
well with the dynamic test prediction after the
“break point.” The Author considers the dynamic
test was the first time the pile experienced sufficient
deflection to generate a resistance of more than
Hastings St Pile 68B Load vs Displacement
0
500
1000
1500
2000
2500
0 5 10 15 20 25
Displacement (mm)
Load(kN)
Static Load
(kN)
Dynamic
Load (kN)
Figure 2 - Hastings St Load vs Deflection
Figure 3 - Hastings St Static Test Reaction Beam
Load vs Displacement - Reaction Beam
0
500
1000
1500
2000
2500
0 5 10 15 20 25 30 35 40
Displacement (mm)
AppliedLoad(kN)
Measured
Expected

4. about 1700kN and so after this point the lower initial
loading stiffness is valid.
The load vs deflection behaviour shown in other
dynamic tests at the site were similar, with similar
initial loading stiffness and stiffness after the “break
point” but they showed a much lower “break point”
and a typical example is shown in Figure 4. The
Author considers this is because these other piles
have not experienced high loading and deflection be-
fore the test as did the static test pile. However the
initial stiffness in these other dynamic tests is still
maintained to higher loads than shown in the first
cycle of the static test. The Author considers the
small blows applied to the pile at the start of each
test cause this and owing to the previous loading by
the small blows the dynamic test results should be
plotted some distance to the right. The pile with
more preliminary blows prior to the “test” blow also
showed a higher “break point” in the prediction of
static load vs deflection, however there were insuffi-
cient tests to say that this behaviour has been
proven. Further analysis of the test data may pro-
vide more information on this behaviour. In particu-
lar it may be worthwhile analyzing several blows
from the one test to assess the change in “break
point.” It is suggested that if it is hoped to avoid this
behaviour that the number of small blows applied
before the full test blows should be minimized. This
would appear to minimize the “preliminary” loading
of the pile and thus provide the best prediction of the
first loading deflection behaviour of a cast in place
pile.
6 CONCLUSIONS
Dynamic testing appears to be just as valid for
bored “cfa” piles as for driven pre-formed piles.
Accuracy of the results for bored piles appears simi-
lar to driven pre-formed piles provided the pile shaft
can be realistically modeled. This requires some
knowledge of the shape of the pile shaft.
The load-displacement behaviour of “cfa” piles in
sand appears to be related to previous load history
with initial loading to any level of load being less
stiff than reloading. Consequently dynamic testing
should be conducted with as few blows as possible if
it is necessary to predict initial load stiffness.
Designers should be aware of low initial load
stiffness. If displacement of this pile type is critical
then pre-loading either statically or by “driving”
should be considered.
7 REFERENCES
G Goble + G Likins (1996) “On the Application of PDA
Dynamic Pile testing” “Proceedings of Fifth Interna-
tional Conference on the Application of Stress Wave
Theory to Piles” Orlando, Florida USA. September,
Townsend, Hussein, McVay Editors. pp263-273
AS2195-1995 “Piling – Design and Installation. Stan-
dards Association of Australia.
Figure 4 - Comparison Pile 68 Static vs Pile 218 Dynamic
Hastings St Piles 68/218 Load vs Displacement
0
500
1000
1500
2000
2500
3000
0 5 10 15 20
Displacement (mm)
Load(kN)
68 Static
Load (kN)
Pile 218 (kN)