Effect of Pipe Stiffness on Maxi-HDD Pull Loads

Abstract

The ASTM standard F1962, Standard Guide for Use of Maxi-Horizontal Directional Drilling for Placement of Polyethylene Pipe or Conduit Under Obstacles, Including River Crossings, provides a procedure for estimating pull loads and stresses on polyethylene (PE) pipe as primarily a function of the drilled path and buoyant weight of the pipe in the borehole. Although the (capstan) effect of tension at route bends is reflected in the analysis, it is assumed that pipe bending stiffness effects may be ignored for the typically very flexible PE material. However, it is of interest to gain a quantitative understanding of the potential impact of such additional factors on the required pull force in somewhat stiffer pipe materials, such as polyvinyl chloride (PVC) or steel. The present investigation therefore focuses on an analytical means of estimating the associated frictional drag forces, allowing an appreciation of the possible importance of such effects and, as appropriate, an extension of the general ASTM F1962 procedure to a broader range of pipe materials. The magnitude of the additional installation forces depends on the bending stiffness of the pipe, as well as the nature of the bend(s) or path curvature and the pipe and borehole dimensions. The results help provide a better understanding of the factors influencing the pull loads in the maxi-horizontal directional drilling (maxi-HDD) installation of pipelines.