Basic HTML Version
30
Geotechnical News • December 2013
www.geotechnicalnews.com
GEOTECHNICAL INSTRUMENTATION NEWS
sections. The RTP-Becker pipe string
is driven using the standard Becker rig
pile driving hammer. RTP measure-
ments obtained during driving provide
detailed information regarding pile
drivability, measurements during static
tests captures load transfer along the
pile, and measurements during pile
setup capture capacity gain over time.
Context and motivation
Improvement in prediction of driven
pile capacity in granular soil is cur-
rently limited due to the factors of
inability to capture the full complexity
of soil deposits and its engineering
behavior with available sampling and
testing techniques, and inability to
accurately model the soil/pile interac-
tion during the pile driving process.
In practice, these uncertainties are
addressed using a large safety factor,
typically ranging from 2 to 4. Fur-
thermore, unexpected stratigraphic
conditions can impact pile drivability
resulting in costly change orders. The
RTP is being developed to remove
some of this uncertainty. The RTP will
be deployed during initial site investi-
gation, and all measurements obtained
available during project bidding. Ide-
ally this would enable engineers and
contractors to increase the efficiency
of pile design and the likelihood of
arriving on site with the correct pile
and installation equipment.
Removable test pile
The design of the RTP system was
guided by the following primary fac-
tors:
• Mobility,
• Commercial integration,
• Durability and robustness,
• Measurement types,
• Measurement sensitivity and
reliability,
• Measurement frequency and
duration.
Of particular challenge, as evident in
previous research, is development of
a system that can withstand dynamic
pile driving and that also has sufficient
measurement resolution to detect
small stress changes during pile setup.
The RTP system assembly is shown
schematically in Figure 1 and photo-
graphs during testing are presented in
Figures 2, 3 and 4. The central compo-
nent is the modular instrumented pipe
sections, which are 61 cm (2 ft) long
with an outer diameter of 168 mm
(6.625 in). Each instrumented section
contains transducers for measurement
of axial force, axial acceleration, pore
pressure, and radial stress. The modu-
lar sections are assembled in series
Figure 1. Schematic of RTP system.
Figure 2. RTP assembly.