Pulling Loads for Polyethylene Pipes in Horizontal Directional Drilling: Theoretical Modeling and Parametric Study

The paper presents an analytical study on the effect of borepath profile, borehole to pipe radius ratio, clearance between pipe and the borehole, and pipe stiffness on the behavior of pipes installed using horizontal directional drilling (HDD). The theoretical model used for the study is presented first. It includes most of the major components of the mechanics of HDD. The borepath is approximated as a series of linear segments and the shape of the pipe in the borepath is found considering pipe stiffness, clearance between the pipe and the soil, and the theory of large deflections of flexible bars. Based on the pipe shape, the contact forces between the pipe and the borepath are calculated. The contact forces cause friction and thus axial pulling force is induced to overcome the frictional forces. The pulling force for the pipe is calculated to equilibrate weight of the pipe and friction between the pipe and the soil and the pipe and the drilling fluid. In order to verify the formulation, the model is used to study the stresses and strains on two pipes that were tested in the field. The developed theoretical model is then used to study the influence of the above parameters on the pulling force applied to the pipe during HDD.