Experimental and numerical analyses of buried box culverts in trenches using geofoam

In embankment construction, earth pressure on buried culverts is reduced either by placing them in a trench in the ground or by inserting a soft zone in the fill over the culvert to create an ‘induced trench’. Although the performance of both methods has been studied in the literature, there are limited findings for applying the two methods in combination. A study was therefore carried out on the earth pressure exerted on box culverts buried in a trench with a soft zone included above. Laboratory tests and numerical analyses were conducted to study the performance of the proposed combined method. A surcharge load was applied to the backfill, and earth pressure around the buried box culvert was measured. After validation of the test results by a numerical method, parametric studies were performed to investigate the effect of the expanded polystyrene geofoam properties and the culvert dimensions. The results showed that culvert installation using the proposed method significantly decreased the earth pressure applied to the walls of the buried box culvert, especially when compared to the trench-only method. Using a width 1.5 times greater than the culvert width and a low-stiffness geofoam, earth pressure transferred to the buried culvert can be significantly decreased.