Axial Pullout Behavior of Buried Medium-Density Polyethylene Gas Distribution Pipes

This paper presents an experimental investigation into the axial pullout behavior of buried medium-density polyethylene (MDPE) pipes under various pulling rates. Tests were conducted in a facility developed at the Memorial University of Newfoundland. During the tests, pipe elongations and axial strains were measured to examine the mobilization of axial force with leading end displacement, and circumferential strains were measured to capture the effects of pipe diameter change. Finite-element (FE) modeling of the tests was used to evaluate the interface friction angle and the effect of diameter changes on the normal stresses on the pipe surface, which influence the pullout resistance of the soil. The results indicated that the pipes' elongation, diameter decrease, and pulling rate significantly influence the pullout forces for buried MDPE pipes subjected to axial ground movement. FE analysis with interface friction angles of 0.75ϕ, 0.86ϕ, and 0.9ϕ was found to successfully simulate the test conditions under pulling rates of 0.5, 1, and 2 mm/min, respectively. Based on the study, simplified methods were proposed to calculate the mobilized frictional length and pipe wall strain from the leading end displacement.