micropiles, have thread type deformations
in accordance with ASTM A
615 requirements for standard rebars.
They provide good bond and adhesion
with the concrete, eliminating the
problems of de-bonding associated
with non-structural access tubes made
of smooth PVC or steel pipes during
CSL testing.
The overall cage stiffness is also
increased by the large, three-inch
diameter, hollow rebars, Figures 3 and
4, making transportation and installation
much easier and safer. Using these
hollow rebars also as a conduit for TIP
wires or probes provides good protection
and eliminates any damage to the
TIP probes.
Since the hollow bars are filled with
water – for placing CSL probes – during
placement of the concrete to eliminate
buoyancy, further research is necessary
not only to test the concrete for
internal anomalies with CSL, but also
to test the extreme outside condition
with the TIP probes inside the water
filled hollow bars. Both CSL and TIP
probes could then be withdrawn for
further usage, making the test not
only much more economical, but also
more complete over the entire crosssection.
Otherwise the TIP probes can
be grouted inside the bars at the time
the concrete is placed.
The following outlines the NDT
conducted at Oregon State University
under Professor Armin Stuedlein,
PhD, with the assistance of Bernard
Hertlein, senior consultant for CSL and
TIP. Figures 5 and 6.
During this experimental program
on four drilled shafts to determine the
effect of high strength steel reinforcement
bars on lateral resistance, TIP,
thermal wires and CSL access tubes
were installed in each shaft and the
corresponding NDT was performed on
each shaft to assess the integrity of the
shafts and to compare the results from
the different NDT methods.
The results of the CSL tests using
scored PVC tubes are compared against
those conducted in the 73/56 (outside/
inside diameter in millimetres) fully
threaded hollow rebars in shaft (HRIS)
in Table 1.
The results indicated that the
hollow rebars served as a good host
for performing the CSL tests. This
paper can serve as a reference to those
interpreting the measurements and
data obtained by performing NDTs on
drilled shaft foundations.
For the HRIS shaft, three No.11 bars
were substituted with 73/56 hollow
fully threaded Grade 80 (552 megapascals
or 80 kips per square inch yield
stress) bars that provided both the necessary
structural requirements and the
access for CSL testing. To prevent the
intrusion into the hollow bar of drilling
fluid and/or concrete during construction,
the base of the hollow bar was
capped with a welded steel plate. The
CSL testing was performed in general
TECHNICAL
Figure 2: Instrumented reinforcement cage
HSIR show the hollow rebars (indicated by
arrows) for CSL or TIP. The blue pipes are
for inclinometers. The lower ends of the
hollow bars are sealed to prevent leakage.
Figure 3 Figure 4
Test Shaft and
Designation
Diameter
m (in)
Casing Wall
Thickness
mm (in)
Internal
and
External
Steel (%)
Table 1. Summary of experimental characteristics of instrumented test shafts. The total
and embedded length of each shaft is 19.8 m (65 ft) and 18.3 m (60 ft), respectively.
Figure 5 Figure 6
Actual
Volume of
Concrete m3
(yd3)
Mild Internal Steel
Reinforcement with
PVC Tubes for CSL (MIR)
0.9 (36) 0 2.00 16.1 (21.0)
High-strength Internal
Reinforcement
and Hollow Rebars
for CSL (HSIR)
0.9 (36) 0 1.50 15.3 (20.0)
Cased, Mild Internal
Reinforcement (CIR)
0.9 (36) 12.5 (0.5) 7.20 13.3 (17.4)
Cased, No Internal
Reinforcement (CNIR)
0.9 (36) 12.5 (0.5) 5.33 13.2 (17.3
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