Axial pipe-soil interaction in ductile iron pipelines with push-on joints: An experimental study

• Perform full-scale axial pipe-soil tests on DN200 DI pipelines with and without push-on joints in medium-dense sand. • Identify a strong influence of burial depth and joint installation orientation on peak axial soil resistance. • Clarify axial strain and circumferential soil pressure mechanisms, highlighting dilatancy and overburden confinement. • Propose an analytical peak axial soil resistance model that accounts for bell-end protrusion and joint orientation. • Improve axial resistance prediction for jointed pipelines in medium-dense sand compared with code-based equations. The pipe-soil interaction (PSI) plays a critical role in the assessment of the serviceability and structural safety of buried water pipelines under external loads, including seismic activity, ground displacement, and fault rupture. Historical earthquake damage investigations have consistently demonstrated that pipeline joints constitute a critical weak link in water supply networks, exhibiting significant vulnerability during seismic events. However, limited existing studies addressed the effects of enlarged outer diameter of push-on joints on axial PSI behavior, resulting in potentially an underestimation of joint response to external loadings. This study investigates the nonlinear PSI behavior through a series of axial loading tests conducted at prescribed loading rates in a custom-designed sand box. The effects of joint type, burial depth, and loading rate on the ultimate bearing capacity and failure modes were investigated in this experimental study. The experimental results indicate that the axial PSI behavior of the buried straight pipe specimen exhibits pronounced rate dependence, with axial resistance forces increasing substantially with loading rate. The enlarged outer diameter of push–on joints induces soil disturbance, leading to distinct surface heaving and tensile cracks in the surrounding soil. This effect gradually increases with increasing pipe specimen burial depth. Notably, the peak axial PSI force of the push–on jointed pipe specimen increased by about 50.6% compared to a straight pipe specimen at a burial depth of 0.8 m. Besides, a modified axial frictional resistance model was developed by incorporating the bulge effect at the bell end of the push–on joint with explicit consideration of the joint orientation. Validation against experimental results confirms the proposed model demonstrates superior predictive accuracy compared to conventional approaches.