Sonic-echo or low strain pile integrity test
Low strain pile integrity testing, known as PIT, is the most
widely used NDT method for the evaluation of deep foundations.
PIT provides a cost-effective and easy to deploy test for
rapid assessment of integrity in piles and deep foundations.
PIT was developed based on the concept of impact-echo and
is customized for slender structural elements.
PIT uses stress waves generated by a hand-held hammer
strike over the pile head. A motion transducer placed on the
pile head records echoes (reflections) from the pile toe or
other internal defects and anomalies. The recorded signal
is amplified, digitalized and used for data interpretation
and analysis.
Ground penetrating radar
GPR can be used to evaluate the sub-surface condition and
configuration of the foundations. It provides a rapid and
cost-effective tool for evaluation of sub-surface soil. It can be
used to identify the location of spread footings and pile foundations.
The selection of GPR antenna frequency depends on
the estimated depth of foundation blocks.
Sub-surface methods
Unlike surface NDT methods, sub-surface methods involve
putting in at least one soil boring or probe on or around the
existing foundation to analyze the foundation. This group
of testing solutions are often more time consuming, more
expensive and often more difficult to execute in the field.
However, the big advantage is higher versatility and reliability.
3 The most widely used NDT methods in this group are:
• Parallel seismic
• Borehole radar
• Borehole sonic
• Cross hole sonic
• Induction field
• Borehole magnetic
How to choose the right test?
In order to select the most reliable and cost-effective testing
solutions, engineers and project managers need to set the
objectives right. The selection of the proper NDT method
relies on accessibility, traffic and complexity of the foundation.
The following general information helps engineers
select the most appropriate test methodology:
• Pile material
• Pile configurations in the foundation layout
• Pile surrounding area (material)
• Pile condition (exposed or covered by pile cap)
• Ground water level
References
1. Department of Homeland Security. (2010) “Aging
Infrastructure: Issues, Research, and Technology,”
BIPS 01, 2010, available at
https://www.wbdg.org/FFC/DHS/bips_01.pdf
(last visited 8 Feb 2020)
2. Rashidyan, Saman. “CHARACTERIZATION OF
UNKNOWN BRIDGE FOUNDATIONS.” (2017).
https://digitalrepository.unm.edu/ce_etds/177
3. Federal Highway Administration & Florida Department
of Transportation, (2010) “Unknown Foundation
Bridges Pilot Study.”
TECHNICAL
Evaluation of unknown foundations in transmission lines
When inspecting existing
structures, it is common to
see that the original pile
and foundation design
information, as well as
installation records, are no
longer available.
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