Abstract:
The Port Access Road (PAR) provides a direct connection from I-26 to the Hugh Leatherman Container Terminal through the former Charleston Navy Complex. The project includes almost four miles of elevated bridge structure which includes eight ramps, an elevated mainline of separated northbound and southbound lanes, and three local access bridges. Structures are supported on drilled shafts, driven square prestressed concrete (PSC) piles, HP section piles, or approximately 1,050, 30-in., 36-in., or 42-in. diameter open-end steel pipe piles which bear within the Cooper Marl. Due to the relatively high calcium carbonate content within the marl, high excess pore pressures are generated when sheared during pile installation, and significant strength gain over time (“setupâ€Â) is assumed in pile design. Relatively small impact hammers can be used to install the large diameter open-end pipe (LDOEP), but larger hammers were used to mobilize the required ultimate resistance, approximately600 to 1200 kips, during restrike driving. High-strain dynamic pile testing was performed on approximately 55 LDOEP during restrike driving with idle periods of 7 to 46 days. Eight of the LDOEP received restrikes during multiple idle times and mobilized resistances on the order of 1,000 to 1,500 kips, which was increase on the order of 10% to 50% between restrikes. The results indicate that significant strength gain continues a week after installation, and that predicted performance under service load is not affected significantly by the increase in ultimate pile bearing resistance over time.