Field Investigation of Pile Setup in Mixed Soil

Abstract

An instrumented test pile was installed at the Bayou Zourie bridge reconstruction site as part of a Louisiana Department of Transportation and Development (LADOTD) research initiative to study the setup phenomenon of piles driven in Louisiana soils. Pile instrumentation included pressure cells to measure the total pressure at the pile face, piezometers to monitor the excess pore water pressure at the pile face, and “sister bar” strain gauges to measure the strain distribution along the pile. Additional instrumentation consisted of multilevel piezometers installed within soils at different locations/depths from the pile and accelerometers attached to the piles during dynamic load testing. A total of two static load tests and four dynamic load tests were conducted on the test pile. During the static load tests, the strains within the pile were measured by the strain gauges, which were used to calculate the distribution of load transfer along the pile. Both static and dynamic load tests demonstrated the increase in pile resistance with time (setup). Results of dynamic load tests confirmed that pile setup occurs at a logarithmic rate after the end of driving (EOD) and is mainly attributed to the increase in side resistance. Good correlation was observed in this study between the pile setup and the percentage of dissipated excess pore water pressure with time. The measured excess pore water pressure suggested that the surrounding soil, along the pile (within distance 2B), is significantly influenced during pile driving. Results indicated that the changes in side resistance are directly related to the changes in the horizontal effective stress acting on the pile face.