Analytical Modeling of Field Axial Pullout Tests Performed on Buried Extensible Pipes

The performance evaluation of buried extensible plastic pipelines, such as polyethylene pipes in the gas distribution industry, in areas prone to ground movement is a key consideration for many utility owners. Considering the relatively smaller deformation stiffness and nonlinear stress-strain response of these pipes compared with those of steel pipes, a good understanding of the basic soil–pipe interaction mechanisms forms a critical part in these evaluations. The increase in soil normal stress on the pipe attributable to soil dilation and gradual degradation of interface friction with axial pipe displacement was investigated. An analytical method was developed to estimate the pipe response when subject to axial frictional loads arising from soil movements, which accounts for these factors and the nonlinear stress-strain response of the pipe material. For a known relative axial soil displacement, the approach provides a convenient way to determine the axial force, strain, and length along which the friction is mobilized. The proposed analytical solution was used to model the response of five large-scale field pipe pullout tests. It is shown that the analytical solution is capable of effectively forming a framework to relate pipe displacement, pullout resistance, strain, and mobilized length. The findings also highlight the significance and need to account for soil dilation effects in describing the soil–pipe interaction in extensible plastic pipes.