Abstract: Large ground deformation such as faults, landslides and liquefaction may pose a serious threat to the structural safety of buried pipelines. This paper presents a series of three-dimensional numerical simulation of horizontal lateral pipe–soil interaction in medium dense sand, discusses the failure mechanisms of sand under different depth-diameter ratios, and examines the influence of depth-diameter ratio on the ultimate bearing capacity of sand. Moreover, a simplified analytical model is proposed based on the failure mechanism of soil around the pipe. According to the limit-state equilibrium theory, the analytical solution of the ultimate bearing capacity under horizontal lateral motion of the pipe is derived. The results show that, in the limit state, the soil around the shallowly buried pipeline forms a rupture surface extending to the ground surface with a failure shape approximately to a logarithmic spiral. The ultimate bearing capacity of sand increases with the burial depth-diameter ratio of the pipe, and finally reaches a constant value at the critical depth-diameter ratio. With the increase of depth-diameter ratio, the pipe displacement required for shear failure of soil also gradually increases. The difference in ultimate bearing capacity calculated by Chinese codes and foreign codes is due to the different empirical lateral bearing capacity coefficient. The analytical solution proposed in this paper can favorably predict the ultimate bearing capacity of soil under lateral horizontal movement of shallowly buried pipes in medium dense sand.

Key words: buried pipe, pipe-soil interaction, medium dense sand, ultimate bearing capacity, failure mechanism