A Case Study on Evaluating Pile Set-up and the Effect of Pile Installation Sequence

This paper examines the set-up behavior of two test piles embedded 139 and 163 ft (145 and 170 ft total lengths) that were installed within 10 feet center-to-center spacing into the coastal soils in Louisiana marsh. The piles were instrumented with strain gauges installed in pairs along the piles’ lengths to measure the load transfer and set-up per individual soil layers. The 145-ft pile was installed 2 hours after the 170-ft test pile. Several dynamic load tests (DLT) and one static load test (SLT) were conducted on the test piles to measure the increase in piles resistances with time. The effect of pile installation sequence on set-up behavior was also investigated. The test results showed that both test piles exhibited significant increase in pile resistances or set-up with time. However, the initial side resistance for the 145-ft pile (installed 2 hours later) was about half the side resistance for the 170-ft pile; and that the rate of side resistance increase with time for the 145-ft pile was much higher than the 170-ft pile. This behavior can be attributed to the sequence of pile driving of close-spaced piles. The driving of the 170-ft pile caused the development of excess pore water pressure in the surrounding soils that affected the initial pile resistance and the set-up rate of the 145-ft pile. The results of this study also indicated that the time, tₒ, to when the set-up curves become log linear with respect to time can be as early as 2 hours after end of driving (EOD). The results of testing program also indicated that the set-up rate parameter “A” is independent of the depth.