Pull-in force predictions for horizontal directional drilling

Horizontal directional drilling is a ‘trenchless technology' that has been used successfully to install pipelines with minimal surface disruption. It has been developed to such an extent that pipelines 2·5 km long and with diameters approaching 2000 mm have been installed, and it has the potential to install pipelines over even greater distances. A study has been undertaken to investigate the use of horizontal directional drilling to create conduits capable of housing electrical cables over long distances (arbitrarily taken as 10 km). This paper presents the results of an investigation into the pull-in forces associated with long-distance horizontal directional drilling installations with different pipe diameters using the Pipe-force 2005 model. The outcomes of the study suggest that if the creation of the borepath can be controlled adequately, then it is theoretically conceivable that pipes of 600 mm diameter could be installed over the maximum distance considered in this project using conventional drilling rigs. However, if the borepath deviates from the desired line and level, or partial borehole collapse occurs, the pull-in force required to install the pipe would increase to a level that would jeopardise installation with currently available equipment.