Field Investigation to Evaluate the Effects of Pile Installation Sequence on Pile Setup Behavior for Instrumented Test Piles

摘要

This paper examined the setup behavior of two 0.61-m (24 in.) test piles (with 44.2-m and 51.8-m lengths) that were installed within 3.05-m (10-ft) center-to-center or 5D (D = Pile Diameter) spacing. The piles were instrumented with strain gauges to measure the load transfer and setup per individual soil layers. The 44.2-m pile was installed 2 h after the 51.8-m 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 setup behavior was also investigated. The test results showed that both test piles exhibited significant increase in pile resistances or setup with time. However, the initial side resistance for the 44.2-m pile ( installed 2 h later) was about half the side resistance for the 51.8-m pile; and the rate of side resistance increase with time for the 44.2-m pile was much higher than the 51.8-m pile. This behavior can be attributed to the sequence of pile driving in clayey soils. The driving of the 51.8-m pile caused the development of excess pore water pressure in the surrounding soils that affected the initial pile resistance and the setup rate of the 44.2-m pile. The CAPWAP analysis of DLT and the load distribution plots from SLTs were used to compute the resistance of individual soil layers along the piles' length with time, which showed that clayey soil layers exhibited higher amount of setup compared to sandy-silty soil layers. The results of this study showed that the time, t(o), to when the setup curves become log linear with respect to time can be as early as 2 h after end of driving. The results of the testing program also indicated that the setup rate parameter "A" is independent of the depth.