86,000 bridges across the United States with no foundation
data on record. Bridge scour susceptibility has been a major
concern for bridges around the globe.2
The same set of challenges exists in the inspection and
testing of the foundations of existing telecommunication and
transmission line towers. The introduction of new communication
systems (i.e. 5G), requires a change in the design of
antennas. Engineers may require additional information on
the foundation of these towers to evaluate performance and
structural reliability.
Another group of unknown foundations belong to street/
highway lighting monopoles and street poles. In the absence
of such information, engineers rely on field inspection results
to evaluate the present condition of the foundation.
Depending on the type of the superstructure, the foundation
system may vary. Foundations can either be shallow
(individual spread footing), or deep (pile foundations). In
the case of deep foundations, the arrangement of piles and
pile cap adds to the complexity of the situation. Moreover,
different soil conditions also affect the selection of proper
investigation technique. A combination of non-destructive
testing solutions and intrusive methods can be used to collect
information about the unknown foundations. These
methods aim to address two of the most important questions
regarding existing foundations:
• Physical shape and dimensions (i.e. pile depth)
• Pile Integrity
The following describes the most common non-destructive
testing methods for evaluating the present condition of
unknown foundations.
Non-destructive evaluation of unknown foundations
Non-Destructive Testing (NDT) methods provide an excellent
tool for evaluating the length and integrity of existing
piles. Different NDT methods have been developed and tested
within the past two decades. A comprehensive study was
performed by the Bridge Maintenance Office of the Florida
Department of Transportation and FHWA3 on the application
of NDT methods for a cost effective and accurate evaluation
of existing unknown foundations. The following describes
some of the most widely recognized testing solutions:
Surface NDT methods
Surface NDT methods do not require any soil boring or probe.
The main advantage with this group is that they are typically
fast with minimal intrusion. The test equipment can easily be
moved around the top of the substructure. The traffic disruption
caused by this group of tests is often minimal. A major
disadvantage to surface NDT methods is their inability to
provide data below a subsurface pile cap.3 The following NDT
methods are widely used:
• Low strain pile integrity test (PIT)
• Bending waves
• Ultra-seismic
• Surface wave spectral analysis
• Ground penetrating radar (GPR)
• Dynamic foundation response
TECHNICAL
CONTINUED ON PAGE 76
Low strain integrity testing
on existing foundation
74 Q1 2020 www.pilingcanada.ca
/Unknown_Foundations_Pilot_Study_02-26-10.pdf
/
/
/www.pilingcanada.ca
