Experimental investigation and seismic performance assessment of cast iron pipelines considering the mechanical property uncertainties of cement-caulked joints

Buried cast iron pipelines suffer serious aging and corrosion after long-term service, resulting in progressive degradation of joint stiffness, strength, and sealing performance. In current urban water supply systems, a considerable number of pipelines still employ rigid cement-caulked joints, yet limited experimental data on their mechanical properties have hindered the development of accurate seismic fragility models. This study addresses this gap by conducting axial tensile tests on full-scale cast iron pipeline joints to examine the influence of pipe diameter and internal water pressure on joint performance. A probabilistic mechanical model is developed based on test results, incorporating the correlation between adhesive strength and cracking opening. The mean adhesive strength is found to be 1.69 MPa with a coefficient of variation of 29 %. The model is integrated into a simplified numerical framework that captures nonlinear soil–pipe interaction and non-uniform seismic excitation, enabling dynamic time-history analyses considering multiple seismic intensities. Results reveal that joints exhibit rapid post-cracking strength degradation and that variability in joint properties leads to significant strain localization. The simulated repair rates, converted from joint leakage failures, align well with empirical data from the Wenchuan earthquake and outperform conventional fragility-based models. These findings highlight the reliability and applicability of the proposed physics-based approach for seismic risk assessment of aging buried pipelines.