A new design method for buried pipes installed in sloping-sided ditches

Abstract

Static and dynamic centrifuge model tests, conducted to investigate mechanical behavior of buried pipes installed in sloping-sided ditches, revealed that the safety of the pipe is critical under vehicle loading applied in the static tests rather than seismic loading applied in the dynamic tests. The static tests were analyzed by using FEM, in which the soil and pipe were assumed to be linear elastic. Small frictional resistance was allowed at the interface between the pipe and the soil by introducing joint elements. Separation, slip failure, and frictional resistance were also allowed at ditch walls by introducing similar joint elements. The analysis generated results that conformed well to the test results, while the current design standards tend to underestimate the safety of the pipes. Thus, design charts for predicting the vertical deflections and the maximum bending moments of the pipes that are buried in sloping-sided ditches with different inclinations of the ditch walls were constructed by using the FEM. A thorough examination showed that the charts can be applied reasonably to any pipe (regardless of different weights, dimensions and materials), any backfill soil (regardless of different soil types, elastic coefficients and weights), and any cover height, leading to the conclusion that the charts can be used instead of the problematical current design methods.