Methods for Estimating Pipe Pullback Loads for Horizontal Directional Drilling (HDD) Crossings

This paper reviews and evaluates three current design practices for calculating tensile loading during the installation of steel and polyethylene pipe using horizontal directional drilling (HDD). A sensitivity analysis of the three models revealed that while the relative influence of the various parameters is a function of the length of pipe within the bore, the predicted pulling load is very sensitive to mud weight and mud drag. This observed sensitivity is not supported by recent published test data. The three design approaches were used to model two recent HDD installations—one a 400-m double crossing of the Grand River, Brantford, Ontario, and the second a 350-m double crossing of the North Saskatchewan River, Edmonton, Alberta. Poor agreement was observed between the model predictions and the field recorded data, both in terms of the trends of the installation loads and the maximum predicted pull head load. It is suggested that additional research is needed to develop a model that better captures the physical reality in the borehole during an HDD installation.