A STUDY OF THE SETUP BEHAVIOR OF DRILLED SHAFTS

Many driven pile foundations exhibit a side shear capacity increase with time, often termed "setup". Previous Florida Department of Transportation (FDOT) research investigating setup capacity reported a setup factor A > 0.20 for five piles driven in Florida soils. Because of their much greater capacity, a similar setup factor for drilled shafts could significantly decrease foundation cost through reduced shaft size, length, or number. The FDOT set aside five drilled shafts at the site of the new SR20 eastbound bridge for future tests following the initial tests performed during construction to verify their design capacity. These shafts ranged from 5 to 7 ft in diameter and 85 to 104 ft in length, with rock socket lengths in limestone 18 to 35 ft long. They were constructed using temporary casing and mineral slurry through overburden soils that included sand, clay, and mixed soils. Loadtest Inc. performed the initial tests in 1996, 6 to 11 days after construction, using multi-level Osterberg Cell (O-cell) tests. Strain gages cast into the shafts provided a shaft load profile from which to estimate the side shear acting on approximately nine segments in each test shaft, three in the rock socket and six in the overburden soils. The University of Florida (UF) performed a second set of tests in 2002, approximately 5.4 years later, focusing on the setup of the shaft segments in the overburden soils. The O-cells and strain instrumentation performed well during the second test set, which was accomplished by staff and students from UF without heavy equipment. This report includes both the 1996 and 2002 tests to insure equivalent analyses. The average side shear setup factor identified for 30 shaft segments in clay, sand, mixed sand and clay, and limestone was A = 0.18. However, the measured setup was both negative and positive, with a median of essentially zero setup. A number of factors, including construction techniques and residual stresses, may have affected the SR20 test results, but predictable side shear setup could not be verified based on these tests. Since potential mechanisms for drilled shaft side shear setup do exist, future tests with more careful research control during the construction and subsequent setup periods may prove otherwise.

Language

  • English

Media Info

  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 462 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00962185
  • Record Type: Publication
  • Report/Paper Numbers: Final Report,, UF PN 49104504798-12
  • Contract Numbers: BC-354 RPWO 32
  • Files: TRIS, USDOT, STATEDOT
  • Created Date: Aug 26 2003 12:00AM