Trenchless Installation Calculations for High Density Polyethylene

High Density Polyethylene (HDPE) is widely used for trenchless technology installations, such as horizontal directional drill (HDD), pipe bursting, sliplining, and compressive fit sliplining. HDPE is a viscoelastic material that allows for a generous allowable bending radius, ruggedness, and durability that are valuable characteristics during trenchless installations. HDPE’s material behavior is unique as its Modulus of Elasticity can vary under time dependent loading conditions which affects the allowable tensile strength of the pipe during installations. General data collection principles for successful design of trenchless technology installations will be provided. Calculations for the pipe installation such as net external loads, average radius of curvature for bore entrance and exit lengths, axial stress along bore path, allowable tensile load, and maximum pull force during HDD will be presented. The realistic construction equipment footprint will be presented for designers to understand equipment constraints that will aid in preparing constructable designs. The construction sequence for pipe bursting, sliplining, and compressive fit sliplining will be provided with discussion on potential points of failure of the process, including unexpected excavations due to repair clamps, changes in existing pipe material, or other items that would halt the advance of equipment. Terzaghi’s theory of soil arching will be presented in order to display how soil behaves during the pipe bursting process as the soil will strengthen as the expander head advances. Available references providing detailed information on calculations and installation procedures will be provided, such as ASTM F-1962 and the Plastics Pipe Institute’s Handbook on Polyethylene Pipe. Actual project examples will be provided in order to help the audience translate the analysis from equations to field installation conditions.