Maxi-HDD Pull Loads for Entry and Exit Points at Different Elevations

ASTM guidelines provide a procedure for estimating pull loads and stresses on polyethylene pipe as primarily a function of the drilled path and buoyant weight of the pipe in the drilled hole. The equations were initially developed assuming a level grade or that the horizontal directional drilling (HDD) entry and exit elevations are the same. In practice, however, it is not uncommon that there would be a finite grade or difference in elevation between the entry and exit points of the drilling operation. The equations and methodology have been expanded to address the placement of polyethylene pipe for the case of a nonlevel grade, including the installation of pipe with and without antibuoyancy measures. The theoretical model and associated results were primarily based on a particular generic borehole geometry, recognizing that specific trends and conclusions may differ somewhat for other possible bore paths. This paper therefore investigates an alternate generic geometry for traversing different entry and exit elevations, representing a reasonable bore path in many practical applications. The results help provide a better understanding of the factors influencing the pull loads in the maxi-HDD installation of pipelines.