United States Department of Transportation
i
Field instrumentation and testing to study set-up phenomenon of piles driven into Louisiana clayey soils : final report.
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2016-07-01
[PDF-6.19 MB]
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Edition:Final report
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Abstract:This research study aims to investigate the pile set-up phenomenon for clayey soils and develop empirical models to predict pile set-up
resistance at certain time after end of driving (EOD). To fulfill the objective, a total number of twelve prestressed concrete (PSC) test
piles were driven in different soil conditions of Louisiana. Detailed laboratory and in-situ soil testing were performed at each test pile
location in order to characterize the subsurface soil condition. Dynamic load tests and static load tests were performed at different times
after EOD to verify the axial resistances of piles and to quantify the amount of increase in resistance (i.e., set-up) compared to the EOD.
The focus of this research was to calculate the resistance of individual soil layers with time along the length of the pile. In order to
implement this goal, all the test piles were instrumented with vibrating wire strain gages. The measurements of vibrating wire strain gages
were used to measure the distribution of load transfer along the length of the pile during the static load tests. Vibrating wire piezometers
and pressure cells were also installed in the pile face in order to calculate the time for dissipation of excess pore water pressure and
corresponding increase in effective stress with time. Case Pile Wave Analysis Program (CAPWAP) was performed in all the dynamic
load test data and used to calculate the side resistance of individual soil layers along the length of the pile during dynamic load tests.
Logarithmic set-up parameter “A” of individual soil layers were calculated using the unit side resistance. The set-up parameter “A” was
correlated with different soil properties such as undrained shear strength, plasticity index, coefficient of consolidation, sensitivity and
overconsolidation ratio (OCR). Three different levels of empirical models were developed to estimate the magnitude of pile set-up with
time. The developed models were used to predict the total resistance of piles in the database at four different time intervals (i.e., 30 days,
45 days, 60 days and 90 days) after EOD. Reliability analyses were performed to calibrate the set-up resistance factor (ϕset-up) for
incorporating it into the LRFD pile design methodology. Accordingly, a set-up resistance factor (ϕset-up) of 0.35 is recommended. A
framework for estimating the duration of pile set-up based on consolidation theory of soils at the pile face was introduced.
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