GETTING THERE IS HALF THE BATTLE – THE LOGISTICAL CHALLENGES OF GEOTECHNICAL INVESTIGATIONS: US 17 WILMINGTON BYPASS, PROPOSED CAPE FEAR RIVER BRIDGE, WILMINGTON, NC

To date the North Carolina Department of Transportation (NCDOT) is in the scoping phase of the geotechnical investigation for a new bridge structure on the proposed US 17 Wilmington Bypass over the Cape Fear River. The proposed bridge is over a mile in length. The NCDOT Geotechnical Unit’s Contracts Group was tasked with providing the drilling services for the investigation. During the initial scoping visits, it was realized that this project is logistically challenging. Access for drilling rigs will require very specialized equipment and personnel. Also, typical ATV drilling machines will not function in portions of the proposed alignment. The structures’ proposed alignment crosses areas that were once rice fields during Wilmington’s Colonial days, wooded Cyprus swamps, the Cape Fear River and several large creeks and ditches. Multiple drilling access methods will be utilized. Barge-mounted drill rigs will be needed to investigate the Cape Fear River channel, as well as Toomer’s Creek. Specialized swamp drilling carriers will be used to navigate the swamps and marsh lands. Track-mounted ATV’s could also be used in the more wooded areas. In the coming months, the Geotechnical Unit will document the different phases of the investigations as we test the limits of the different drilling equipment. Most of the equipment needed the NCDOT does not have in-house and will have to be outsourced. Geologists working in the geotechnical field have to be able to do more than describe a sites geologic framework. Many times the geologist is given the responsibility of getting drilling equipment into places that seem too difficult. In this case the bridge foundations cannot be designed without subsurface data, so the geologist must find a way to make the investigation happen.