Phase 2: Field investigation and pile installation and load testing
This Phase included site characterization of the selected test site, installation of piles for axial and lateral testing, and the execution of the load tests.
Site characterization activities at the test site comprised:
- Standard penetration testing (SPT)
- Seismic piezocone penetrometer testing (SCPTu)
- Standard and novel piezocone penetrometer testing (CPTu)
- Continuous borehole sampling using split spoon samplers, Shelby tube samplers, and Denison samplers
- Collection of disturbed glauconite sands from the outcrop location near the test site
Pile installation and load testing included:
- Driving various size piles with redrives following pause periods and restrikes
- Lateral load testing
- Axial compression and tension load testing
- Pile extraction and pile-wall soil sampling
Nine carbon steel pipe piles were adopted for the field-testing program. Five smaller diameter piles with an outer diameter (OD) of ~0.32 m were driven to depths between ~15 to 20 m for a length-to-diameter ratio up to 66.
One of the smaller diameter piles was open-ended to investigate plugging and included an internal shoe 9.5 mm in thickness and 10 cm in length. Two of the smaller diameter closed-ended piles included external shoes, one with a single shoe at the toe of the same dimensions and one with multiple shoes spaced 4.6 m apart along the length of the pile.
Four larger diameter piles have an OD of ~1.5 m and were driven to ~15 m depth for a length-to-diameter ratio of 10. All four piles had internal shoes 25 mm in thickness and 10 cm in length. Two of the piles included an external shoe of the same dimensions to investigate the effect of reductions in shaft friction.
Selected piles were fitted with internal and/or external driving shoes to examine their impact on soil plugging behavior and reduction in shaft friction during installation and subsequent static loading.
During the installation of the piles with pile driving hammer, all piles were instrumented with strain gauges connected to a Pile Driving Analyzer (PDA) unit. Selected piles also had Fiber Bragg Grating (FBG) fiber optical sensors embedded along their length to measure strain during vertical and lateral static load testing.
Instrumentation redundancy comprising load cells, extensometers, tiltmeters, and dial gauges was utilized to provide a range of load and displacement behavior of the tested piles.