Stress Reduction by Ultra-Lightweight Geofoam for High Fill Culvert: Numerical Analysis

Abstract

The study of earth pressure distribution on buried structures has a great practical importance in constructing highway embankments above pipes and culverts. Based on Spangler's research, the supporting strength of a conduit depends primarily on three factors: 1. the inherent strength of the conduit; 2. the distribution of the vertical load and bottom reaction; and, 3. the magnitude and distribution of lateral earth pressures which act against the sides of the structure. Considering high fills above them and high earth pressures they may experience, rigid culverts are usually used underneath highway embankments. To reduce high vertical earth pressures acting on buried structure, ultra-lightweight Geofoam was placed above a culvert in the field, in Russell County, KY. Before construction began, numerical analysis using FLAC 4.00 (Fast Lagrangian Analysis of Continua) had been performed to predict stresses on the culvert. Results of the analysis show that Geofoam has a great effect in reducing vertical stresses above and below the culvert. There were areas of high stress concentrations at the top and bottom of the concrete culvert if no Geofoam was placed above the culvert. After placing Geofoam above the culvert, the concentrated stress at the top can be reduced to 28 percent of the stress without Geofoam. The high stress at the bottom of culvert can be reduced to 42 percent of the stress without Geofoam. Stresses on the two sidewalls of the culvert were observed to have no significant change in values with and without Geofoam.