Ultimate bearing capacity of sand under lateral movement of buried pipelines

Permanent ground deformation hazards, such as fault displacement, liquefaction-induced settlement, and landslides, pose a severe threat to the integrity of buried pipelines. In this study, three-dimensional numerical simulations are performed to investigate the horizontal lateral soil-pipeline interaction in medium-dense sand and to identify the failure mechanisms of the surrounding sand for different pipeline depth-diameter ratios. The ultimate bearing capacity of sand around the pipeline is evaluated for different soil failure mechanisms. Moreover, a simplified analytical model of the soil-pipeline under lateral movement is proposed based on the identified soil failure mechanisms. Consequently, an analytical solution for the ultimate bearing capacity of the soil under lateral motion of the buried pipeline is derived based on the limit-state equilibrium. The results obtained from the analytical solution indicate that at the limit state, the soil around a shallowly buried pipeline forms a ruptured surface extending to the ground surface with a logarithmic spiral failure surface. The lateral ultimate bearing capacity increases as the pipeline burial depth-diameter ratio increases until it reaches a constant value at a certain critical depth-diameter ratio. As the pipeline depth-diameter ratio increases, the pipeline displacement that causes shear failure of the soil also gradually increases. It is demonstrated that the proposed analytical solution well predicts the soil ultimate lateral bearing capacity for pipelines installed shallowly in medium and dense sand. Furthermore, the ultimate bearing capacity of pipelines in sand is evaluated by Chinese and some international codes. The disparity between results from different codes is attributed to the variation in empirical lateral bearing capacity coefficients used in the respective codes.