Static and Seismic Performance of Culverts with Lightweight Backfills

California’s highway system includes hundreds of thousands of culverts and drainage facilities, many of which are aging and may be vulnerable to earthquake-related damage. Replacing these structures can be costly and disruptive, creating a need for practical approaches that improve their resilience while extending their service life. Lightweight fills weigh substantially less than conventional earth fills and therefore have the potential to reduce the forces imposed on buried culverts; however, their benefits under earthquake loading have not been systematically quantified. This project will investigate whether, and to what extent, lightweight fills placed above and adjacent to culverts can reduce demands on these structures under both normal and earthquake loading compared with conventional earth fills. The research will identify representative culvert types and configurations in California, experimentally characterize selected lightweight fill materials, and develop computer models calibrated using available field or laboratory measurements. These models will then be used to evaluate the performance of representative culverts under a range of conditions and California-relevant earthquake motions. The results will be used to identify where lightweight fills provide the greatest benefit and to develop practical recommendations for their use in culvert rehabilitation and design. Ultimately, the research will provide Caltrans with information and guidance to support safer, more resilient, and cost-effective management of culverts within California’s highway system.