Seismic Retrofit of Bridge Foundations: Piles, Ground Improvement and Buttress Berms

January 7, 2026

Many aging bridges across western North America are seismically vulnerable, particularly those built before modern seismic codes. Full replacement is often cost-prohibitive, making seismic retrofitting a more practical solution to enhance structural resilience. This paper synthesizes foundation retrofit methods used in British Columbia, Canada, based on the authors’ experience with major bridge projects. Three main retrofit approaches are discussed: (1) foundation strengthening with new piles, (2) ground improvement, and (3) buttress berms. Structural (direct) retrofits involve installing piles adjacent to existing foundations and connecting them at the pile cap to transfer seismic loads to more competent soils or bedrock. Geotechnical (indirect) retrofits aim to strengthen or densify foundation soils to mitigate the effects of liquefaction and strain softening. Techniques include timber compaction piles, vibro-replacement, compaction grouting, deep soil mixing, and rammed aggregate piers. Hybrid strategies combining structural and geotechnical methods are frequently employed due to varying site conditions and construction constraints. Case studies from four Fraser River crossings—the Agassiz- Rosedale, Mission, a Railway, and Knight Street bridges—demonstrate how tailored retrofit strategies addressed challenges such as liquefiable soils, constrained work zones, environmental sensitivity, and active traffic.

Thavaraj, T., Greinacher, K, 2025 " Seismic Retrofit of Bridge Foundations: Piles, Ground Improvement and Buttress Berms,” in Proceedings of the GeoManitoba 2025 Conference, 21-24 September 2025, Winnipeg, Manitoba: (CGS and CPA)