Finite Element Analysis of Deeply Buried Flexible Pipes

Residue underdrains in tailings storage facilities are commonly buried under high fills. Flexible plastic pipes are normally used, the material being either PVC or HDPE. The performance of flexible pipes under large heights of tailings is relatively unknown. Guidelines for the design of buried flexible pipelines are presented in Australian Standard 2566.1. However, these are mainly for shallow burial of pipes. The main limitation of existing design methods is that the effect of arching is ignored. Many pipe designers use the prism load routinely even when considerable arching occurs. This often leads to conservative designs which are not cost-effective. A new bauxite residue disposal area to be developed at Worsley in Western Australia was used as a case study. The residue underdrains will be buried under 70 m of tailings and therefore subjected to very high overburden pressures. Due to the limitations of existing design methods, finite element analysis (FEA) was used to model the pipes. FEA can simulate the complex interaction between the pipe and soil more accurately than other methods. Several factors which influence the structural performance of flexible pipes were examined and the results are presented in this paper. The advantages of using FEA over conventional design methods are discussed.