CASE HISTORY: HORIZONTAL DIRECTIONALLY DRILLED PIPELINE CROSSING OF THE ATCHAFALAYA RIVER AT MELVILLE, LOUISIANA

Development of horizontal directional drilling (HDD) design procedures is examined by detailing a state-of-the-art (at the time of execution in 1987) trenchlessly placed river crossing: a high-pressure natural gas pipeline 976 m (3,200 ft) long and 915 mm (36 in.) in diameter installed beneath the Atchafalaya River in south central Louisiana. The pipeline was near an existing pipe suspension bridge and numerous conventionally placed lines, most of which had been affected by river scour. Unique project features are the crossing's large diameter and length coupled with its being the first subdrilling (in the United States) of a major, publicly owned flood protection levee. The site history and river channel/subsurface conditions are described. These factors led to selection of the crossing's implementation methodology and geometry and the decision to subdrill the levee. Development of the installation's design is reviewed, and the efforts inherent to construction permitting are highlighted. The actual construction is described, with concentration on solutions to problems encountered. An analysis of the effects this installation has had and is having on HDD design and construction is then presented in conjunction with recommendations for improving future HDD engineering.