Non-Destructive Testing of Unknown Bridge Foundation Lengths Using Parallel Seismic Testing-PPT Presentation

PPT Presentation

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The presentation describes Parallel Seismic Testing (PST), a non-destructive method for determining the lengths of existing bridge foundations when construction records are unavailable. Knowing pile length is important for scour assessments, service-life evaluations, retrofits, and reuse. PST is widely regarded as accurate across varied bridge substructures and soil conditions.<br /><br />PST uses a water-filled, cased borehole installed beside and below the estimated pile tip. An instrumented hammer generates waves in the structure; a hydrophone in the borehole records their arrival as it is raised in one-foot increments. The resulting data are used to identify the pile tip.<br /><br />Two Florida bridge projects illustrate the method. At the Green Bridge, a 1986, 48-span structure on prestressed concrete piles, a budget-conscious program combined PST, low-strain integrity testing (LSIT), and calibration tests. PST estimated pile lengths within one to two feet of refusal-limestone depths. Calibration improved LSIT reliability, though its estimated accuracy was about 11 percent.<br /><br />At the Southern Boulevard Bridge, built in 1950, PST was used to assess whether construction of a nearby replacement bridge could affect the existing bascule piers. Two test locations indicated pile lengths of approximately 27 and 27.5 feet. A third result was judged to reflect sheet-pile length rather than foundation-pile length. During later demolition, exposed piles measured 28–30 feet, corroborating the earlier PST findings.<br /><br />The case studies demonstrate that PST can provide reliable foundation-length measurements even in complex conditions, including battered piles, waterline footings, and cofferdam footings. These measurements can support consequential engineering and financial decisions, such as refining scour protection or determining whether a bridge can remain in service during nearby construction.

Keywords

Parallel Seismic Testing

PST

bridge foundations

pile length

non-destructive testing

scour assessment

low-strain integrity testing

hydrophone

bridge retrofit

foundation evaluation