DETERMINING THE EFFECT OF STAGE TESTING ON THE DIMENSIONLESS PILE SIDE SHEAR SETUP FACTOR

The research work described herein follows previous Florida Department of Transportation (FDOT) research published by Bullock (1999) and by McVay, Schmertmann, Townsend, and Bullock (1999), which investigates the change in pile side shear capacity with time. Many piles exhibit a capacity increase, termed "setup" or "freeze." Although casually observed by many engineers and contractors, research documentation of setup is limited and design methods do not routinely include it. The previous FDOT research investigated setup and determined the "Setup Factor A" for five piles in Florida soils. However, this research was performed by testing the same piles repeatedly, a commonly accepted test method referred to as "staged" testing. The possible effects of staged testing were not determined during the previous work and provided a caveat to the results. Bullock (1999) also introduced the standard penetration test with torque measurement (SPT-T) as a cost-effective precursor insitu test for pile setup. The research described herein uses the SPT-T to investigate staged testing adjacent to the test pile driven during the previous research at the Seabreeze Bridge in Daytona Beach, Florida. Twelve borings provided SPT-T results in two soil layers: a silty sand and a shelly clay. Staged SPT-T tests were conducted in three of the borings at nominal times of 5, 30, 180, and 1080 minutes after the driving of the SPT sampler, and unstaged tests were conducted in the remaining nine borings at similar times. Similar to the Vilano Beach sands, the SPT-T results in the Seabreeze sand layer did not exhibit setup, and were not useful for investigating staged testing effects. However, the Seabreeze clay did indicate significant unstaged side shear setup, and the staged tests measured a 150% increase beyond the unstaged side shear. This yields a ratio of A(unstaged)/A(staged) = 0.4, which is further supported by test pile data published in the literature. Side shear setup from staged pile tests in clay at both the Seabreeze and Vilano Beach sites also correlated well with staged SPT-T side shear setup, further validating the SPT-T as a setup predictor test.