The Use of Foamed Glass Aggregate (FGA) as a Lightweight Fill Above Culverts

Transportation infrastructure—including buried utilities, drainage systems, and culverts—is frequently subjected to significant external stresses arising from existing conditions and new construction, especially in urban environments where deformation and failures can lead to significant operational and safety consequences. Lightweight fills offer a viable strategy to mitigate these stresses by reducing imposed loads. This study investigates the use of lightweight fills, specifically Foamed Glass Aggregate (FGA), as a sustainable solution to support California Senate Bill 1 (SB1) efforts to repair and maintain culverts, as well as for new construction applications. A numerical investigation was conducted to evaluate the performance of culverts backfilled with FGA compared to conventional fills. Models were developed for reinforced concrete box culverts and corrugated steel pipe culverts, and parametric analyses were performed across a range of configurations. Results indicate that FGA significantly reduces soil stresses, structural demand, deformation, and settlement compared to conventional fills. This study also developed design and construction guidance and proposed updates to Caltrans manuals to facilitate implementation in practice. The findings demonstrate that FGA is an effective, sustainable alternative for improving culvert performance in California and beyond, helping agencies better address aging infrastructure and increasing construction demands.