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 $10\mathrm{m}$ . The increasing use of difficult terrains for infrastructure, landfills, and residential and industrial developments has prompted installation of drainage pipelines under $20–30\mathrm{m}$ high fills. This paper presents the behavior of an instrumented flexible pipe buried under a $47.1\mathrm{m}$ deep fill. For filling above $20\mathrm{m}$ , 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 Spangler’s 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 $>20\mathrm{m}$ . 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.