Effectiveness of Viscoelastic Models for Prediction of Tensile Axial Strains during Cyclic Loading of High-Density Polyethylene Pipe

High-density polyethylene (HDPE) pipelines are commonly installed using horizontal directional drilling (HDD), a trenchless construction technique used to replace or expand underground pipelines which generates cyclic axial forces on the pipe. To evaluate the ability of existing linear and nonlinear viscoelastic models to predict HDPE pipe response during this cyclic loading, calculations of axial strain are compared with the laboratory measurements. The linear viscoelastic and nonlinear viscoelastic models provide reasonable estimates of the maximum strain levels during installation; however, maximum strains were underestimated by the linear viscoelastic model and overestimated by the nonlinear viscoelastic model. During periods of strain reversal, both models overestimated the amount of axial strain recovery. A parametric study showed how the magnitude of these strains depends on the peak stress during each cycle, the number of cycles, and the period of time stresses are applied. The work also quantifies how increases in peak stress and the number of cycles increase the maximum axial strain. Conventional creep functions can provide reasonable conservative estimations of the maximum strain during a HDD installation provided that the maximum pulling force is known.