Behavior of Buried Flexible Pipe under High Fills and Design Implications

The existing design guidelines for buried flexible pipes are limited to depth up to 10 m. The increasing use of difficult terrains for infrastructure, landfills, and residential and industrial developments has prompted installation of drainage pipelines under 20–30 m high fills. This paper presents the behavior of an instrumented flexible pipe buried under a 47.1 m deep fill. For filling above 20 m, the measured vertical stress above the pipe exhibited a concave distribution, corresponding to 90 and 110% of the average vertical pressure at the center and edges of the pipe, respectively. The measured results suggest that a triangular lateral pressure distribution can lead to overly conservative and uneconomical results for high fills while Spanglerʹs analysis is unconservative. Based on the measured results, a revised vertical and lateral earth pressure diagram was proposed for the design of flexible pipe under high fills >20 m. This paper proposes closed-form analyses for estimating the moments and displacements of the pipe subjected to high fill earth pressures. These closed-form solutions agree well with the measured pipe displacements and strains.