Soil-structure interaction behind integral bridge abutments

Integral bridges are preferred on infrastructure schemes as they have lower maintenance costs than a conventional jointed bridge. A key aspect of integral bridge design is the assessment of long-term passive resistance that develops in the abutment backfill due to seasonal movements of the superstructure. This resistance is currently defined by an intermediate earth pressure coefficient termed K*, and is typically evaluated using the limit equilibrium (LE) approach prescribed in BSI PD-6694-1:2011+A1:2020. This paper adopts the alternative numerical design approach and investigates the development of K* behind full-height abutments using soil-structure interaction (SSI) modelling in Plaxis-2D software. The study demonstrates that mobilised passive resistance is primarily a function of backfill and structural stiffnesses, and that the current LE approach does not capture the backfill resistance profile correctly. The effectiveness of the SSI method was verified by comparison to the LE method. The current study provides an SSI methodology that is an efficient design approach, and which is suitable for a wide variety of integral bridge arrangements beyond the current LE method applicability.