PILE FRICTION FREEZE: A FIELD AND LABORATORY STUDY. VOLUME I AND VOLUME II

The objectives of this research were to measure the increase in pile friction with time for various soil conditions in the laboratory and field. Accordingly, five fully instrumented piles were driven into a variety of soils at four different Florida Department of Transportation (FDOT) bridge sites. The five 18-in. (457-mm) square piles were instrumented with strain gauges, lateral total stress cells, and pore pressure sensors along their length, and at their tips were cast Osterberg load cells. This study was the first application of an Osterberg load cell on a prestressed concrete pile to generate ultimate skin friction. In the laboratory, a device was developed to drive a model pile in the centrifuge in flight at 50 gs and then perform a static pullout (tension) test. Also, in the field Standard Penetration Tests with Torque (SPT-T), piezo cone penetrometer (CPT), and Marchetti Dilatometer (DMT) stage testing was performed to estimate the pile freeze (setup) with time. The centrifuge stage tests showed no increase in pile friction with time. The field load tests to monitor freeze were performed on the day of driving and then by stage testing and at 3 to 5 times thereafter, with a final test at 77 to 1,727 days. All pile and pile segments showed a general increase in friction with the log of time. All soils, from sands to clays, showed about the same freeze as measured by a normalized shear and time factor, denoted 'A'. Furthermore, 'A' was found approximately the same at all depths to the maximum of 24 m tested. 'A' was also found approximately the same whether measured by redrives the first few days after driving, or by static tests during or after the dissipation of the driving pore pressures. The freeze appeared effective stress dependent during dissipation, but independent afterwards. The SPT-T showed the most promise as a practical precursor test for freeze in cohesive soils, followed by the CPT and DMT. None of these tests showed promise in sands.