A Unique Drilling System--Nearshore/Surfzone, Oregon Inlet, North Carolina

Abstract

The design of twin jetty structures at Oregon Inlet, North Carolina required extensive knowledge of the geotechnical properties of the sediments on which the jetties were to be sited. The greatest proportion of the jetty foundations were within the shallow-water shoals, surfzone, and nearshore waters at the inlet entrance. Because of the wave climate on the shoals and the varying water depths, standard methods of siting a drill for geotechnical sampling and testing could not be employed on the site. Drilling, sampling, and in situ soils testing required that any drill site might have to be occupied for as much as four days, in water as shallow as 3 ft or as deep as 10 ft and withstand waves as high as 5 ft. The method selected and developed by the Geotechnical Branch, Wilmington District, U.S. Army Corps of Engineers was a helicopter-transported steel platform 12 ft wide × 16 in. long × 20 ft high, capable of supporting a drill rig, such as a Failing 43SA or Longyear 150, and all associated equipment.