Bearing capacity mechanisms for pipes buried in sand
Jinbiao Wu, George Kouretzis, Laxmi Prasad Suwal
Abstract
This paper presents results of scaled physical model tests performed to measure the reaction developing on a rigid pipe buried in dry sand when the pipe is subjected to vertical downwards movement relative to its surrounding soil. The aim of this experimental study is to evaluate the efficacy of methods used to determine the properties of vertical bearing springs, an integral part of beam-on-nonlinear Winkler spring models used for the analysis of buried pipelines subjected to permanent ground displacements. We show that bearing capacity formulas used in practice to estimate the ultimate reaction developing on buried pipes may provide reasonably accurate estimates, provided that they are used together with sand friction angle values that account for the fact that granular materials do not obey an associative flow rule, and with bearing capacity factors compatible with the mode of sand failure observed in the tests. We also provide evidence suggesting that laying pipes in loose sand backfills does not have a beneficial effect on the reaction developing on the pipe, compared to medium dense sand, and we recommend against using loose sand material properties for the estimation of the properties of vertical bearing springs.