Performance of flexible buried pipes reinforced by geogrids under cyclic loading

The study on protection performance of buried pipes under cyclic loading has been increasingly concerned. Firstly, a series of laboratory tests are conducted to investigate the mechanical performance of buried pipes during cyclic loading when the buried depth of pipes is 3D (D, external diameter of pipes). The results show that the optimum embedment depth of the uppermost reinforcement, spacing of geogrid layers and length of reinforcement are 0.4B (B, width of loading plates), 0.5B and 5D, respectively. Adding the numbers of layers of geogrids can significantly enhance the strength of soils and thus reduce the deformation of pipes and settlements of loading plates. It is pronounced that higher level of loading or lower frequency can affect remarkably the mechanical performance of buried pipes. Increasing the level of cyclic loading or lowering frequency of loads can result in the increase of radial deformations of pipes, settlements of loading plates and strains of geogrids. The strains of reinforcement decrease with the increase of distance away from the center of loading plates, and those of geogrids in the center tend to increase firstly and then decrease with the increase of cycles of loads. Furthermore, based on the numerical simulation method, the mechanical properties of pipes under different buried depths of pipelines, H, width of loading plates, B, and pipe diameter, D, are presented. The increasing buried depth or decreasing width of loading plates may reduce the radial deformations of pipes. The reinforcement effect is weakened for the pipes with smaller diameters, leading to the increase of deformations of pipes. However, the reinforcement plays a significant role in reducing the deformations of pipes with greater diameters.