Mechanical behavior and failure mechanism of buried pipelines with anti-pullout bell-socket joints under strike-slip fault dislocation

The damage of water-supply pipelines under fault rupture primarily concentrates at the pipe joints, which are the weakest structural links of the pipelines. Based on the traditional bell-socket joint of water supply pipelines, the rubber gasket and metal limit ring are introduced in the joint configuration, and a new type of anti-pullout bell-spigot is proposed. The new joint allows certain tensile-compressive and rotational deformations before the service limit state under daily operation. When the axial deformation of the joint reaches a certain level, a self-locking mechanism is triggered to prevent the joint from the pullout damage. The self-locked joint in turn leads to the relative movement between the adjacent pipe segments and the surrounding soil, and forms a chain effect, which effectively overcomes the excessive pipeline deformation caused by the fault dislocation. To assess the performance of water-supply pipelines incorporated with the proposed anti-pullout bell-spigot joint under strike-slip fault, the influences of the critical factors such as pipeline burial depth and pipeline-fault angle are investigated based on the numerical analyses of a three-dimensional nonlinear pipe-soil interaction finite element model. The results show that the pipelines incorporated with the anti-pullout bell-spigot joint can accommodate a strike-slip fault displacement 4 times of that for a traditional joint, and its failure mode of the joint changes from the pull-out failure to the excessive bending one. Moreover, for a shallowly buried pipeline with a fault crossing angle of 120°, the proposed joint can most effectively improve the resistance of the segmented pipelines against strike-slip fault movement. Overall, improvement of the axial tensile bearing capacity of the pipe joint is the key to improve the performance of segmented pipelines subjected to large ground deformation.