Theoretical model for calculating pulling loads for pipes in horizontal directional drilling

The paper presents a model for calculating installation loads imposed on pipes during the pulling operation in horizontal directional drilling. The model is implemented into a numerical program PipeForce 2005. The analysis includes pulling load contributions from directional changes, fluidic drag, solid friction and pipe’s weight. The emphasis in this paper is on details related to directional changes during the HDD installation. The formulation approximates the borepath as series of linear segments between the measured points (field-measured locations of the drilling head) and predicts the shape of the pipe in the borepath. Based on this shape, the layout of the borepath and the pipe stiffness, the contact forces between the pipe and the borepath are evaluated using the theory of deflections of flexible bars. The pulling force for the pipe is calculated to equilibrate the weight of the pipe and friction between the pipe and the soil and between the pipe and the drilling fluid. A comparison of theoretical predictions and field data is presented.