I-26/Port Access Road Interchange
The new Port Access Road provides a direct connection from I-26 to the Hugh Leatherman Container Terminal under construction on the former Charleston Navy Complex in North Charleston, South Carolina, while maintaining service for local, commuter, and commercial traffic.
The project was exposed to a high seismic hazard, and it was constructed some eight miles of large bridge structures and associated roadway embankments through highly variable subsurface conditions that include significant uncontrolled fill deposits, liquefying sand strata, and highly compressible clay strata through the historic industrial “neck” area of the Charleston peninsula.
S&ME produced significant geotechnical and environmental site characterization for the SCDOT in preparation of the design-build RFP. This included a non-linear site-specific response analysis to provide ground motions for use in the geotechnical and structural design.
As part of the design-build team, S&ME performed significant additional geotechnical explorations to more fully characterize the numerous ramps and roadway alignments. Ground improvement using earthquake drains, surcharging, and column-supported embankments are used to construct approach embankments and reduce seismic loads on foundations. The geotechnical and bridge designers collaborated closely to develop cost-effective foundations that meet the stringent SCDOT performance requirements in adverse soil conditions with a large seismic hazard.
During construction, S&ME confirmed the design by performing high-strain dynamic testing with a Pile Driving Analyzer (PDA) during installation and restrike driving of 13 H-piles/composite pre-stressed concrete piles at the local access roads and 61, 30-in. to 42-in. diameter open-end pipe piles at the Mainline and ramp structures with pile lengths of over 100 ft and ultimate bearing resistances of up to 1,150 kips. During the CEI firm’s foundation testing of the drilled shaft foundations, S&ME reviewed the crosshole sonic logging (CSL) and thermal integrity profiling (TIP) reports for determination of shaft integrity and performance.
S&ME’s services also included pre-and post-construction condition surveys of 104 residential and 19 commercial structures prior to construction activities, and vibration monitoring at up to four locations during demolition and construction, including drilled shaft casing installation, earthquake drain installation, pile driving, and MSE wall construction. During the pre-construction condition survey phase, crack gauge devices were installed on various structures to monitor any movement of existing cracks.