Study of non-uniform bedding support under continuous PVC water distribution pipes

Current design standards for buried pipe installations assume that loading and bedding conditions along pipes are uniform, and thus do not take into account the effect of soil variability. However, although careful attention may be paid during pipe installation, there is still a possibility that a pipeline may experience non-uniform loading or bedding conditions during its lifetime, which may lead to pipe failure. Thus, these conditions should be addressed to understand the implications of construction practice and problems that may be detected after construction. In this paper, a parametric study employing three-dimensional finite element analysis is used to examine a continuous PVC water pipe. The objective is to understand the effect of non-uniform bedding support on the stability of buried PVC pressure pipes, and the longitudinal soil-pipe interaction. The numerical analyses are performed using ABAQUS. The results of the finite element analyses demonstrate that pipes with discontinuous bedding experience stresses higher than those with uniform ground support (37-69% higher for medium dense sand, and 45-95% higher for dense sand bedding), and that it is better to achieve uniform soil support under the pipe invert than to achieve non-uniform support in high stiffness (highly compacted) bedding (results that support conventional wisdom where a layer of uncompacted bedding is used under the invert in preference to well compacted bedding that is not level). The analysis also indicates that it is more important to achieve that uniform support under the invert than dense soil backfill under the haunches.