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The Easy Button for Driven Pile Setup: Dynamic Testing
Field inspectors often observe a dramatic increase in penetration resistance between initial driving and restrikes of driven piles, a result of additional static "setup" capacity. Designers often ignore setup when specifying pile lengths and blow count acceptance criteria, and pile capacity design methods, calibrated against static load tests, already incorporate some setup that occurs during the test preparation delay. Research indicates that setup results mostly from an increase in side shear and occurs in all soil types as a result of combined pore pressure dissipation, consolidation, and mechanical aging effects. Repeated static tests provide a reliable measurement of setup, but also delay construction. Penetration resistance (set per blow) does not reliably measure setup during isolated restrikes as it varies per blow due to inconsistent driving system performance and changing pile capacity. Instrumented dynamic tests, using strain gages and accelerometers, provide an "easy button" to verify hammer energy and pile capacity during all phases of installation. This paper reviews pile setup, its causes, and related properties. It presents a simple method, with examples, to measure and analyze setup from dynamic test results. An engineer may use these results to reduce the length, size, or number of production piles, and adjust the required set per blow. Caveats include staged testing effects and consideration of the setup contribution from different soil strata.
The Easy Button for Driven Pile Setup: Dynamic Testing
Field inspectors often observe a dramatic increase in penetration resistance between initial driving and restrikes of driven piles, a result of additional static "setup" capacity. Designers often ignore setup when specifying pile lengths and blow count acceptance criteria, and pile capacity design methods, calibrated against static load tests, already incorporate some setup that occurs during the test preparation delay. Research indicates that setup results mostly from an increase in side shear and occurs in all soil types as a result of combined pore pressure dissipation, consolidation, and mechanical aging effects. Repeated static tests provide a reliable measurement of setup, but also delay construction. Penetration resistance (set per blow) does not reliably measure setup during isolated restrikes as it varies per blow due to inconsistent driving system performance and changing pile capacity. Instrumented dynamic tests, using strain gages and accelerometers, provide an "easy button" to verify hammer energy and pile capacity during all phases of installation. This paper reviews pile setup, its causes, and related properties. It presents a simple method, with examples, to measure and analyze setup from dynamic test results. An engineer may use these results to reduce the length, size, or number of production piles, and adjust the required set per blow. Caveats include staged testing effects and consideration of the setup contribution from different soil strata.
The Easy Button for Driven Pile Setup: Dynamic Testing
Bullock, Paul J. (author)
Symposium Honoring Dr. John H. Schmertmann for His Contributions to Civil Engineering at Research to Practice in Geotechnical Engineering Congress 2008 ; 2008 ; New Orleans, Louisiana, United States
2008-03-07
Conference paper
Electronic Resource
English
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