Investigation into soil ratcheting behind integral bridges using centrifuge modelling

Abstract

U.K. integral bridges are commonly designed according to PD 6694-1, with guidance on backfill ratcheting based on experimental data that is limited by: testing at a small-scale low stress state, a lack of abutment foundation and soil below, and a limited range of soil-structure configurations. As integral bridge use increases, there is a need for further understanding of the strain ratcheting mechanism which can lead to smarter designs that minimise material usage and lifetime maintenance. This research presents the suitability of modern centrifuge techniques to simulate ratcheting of the soil behind an integral bridge abutment over a design life of thermal loading. A high accuracy actuation system was developed and used in centrifuge testing, with test data provided to demonstrate its capabilities. This is followed by a comparison of surface settlements, deck axial forces and abutment bending moment distributions recorded for various soil-structure combinations, highlighting the sensitivity of soil ratcheting. The paper concludes that centrifuge modelling can successfully simulate backfill strain ratcheting behind integral abutments over a range of soil-structure configurations. Furthermore, results suggest that global rotations and base sliding are significant to the overall response, clarifying the importance of modelling at an appropriate stress state with a foundation and the soil below.