Application of engineered compressible inclusions to mitigating soil-structure interaction issues in integral bridge abutments

Abstract

The thermally induced cyclic loading on integral bridge abutments causes soil deformation and lateral stress ratcheting behind the abutment wall due to the expansion and contraction of the bridge deck. The forward and backward movements of the abutment in response to the expansion/contraction of the bridge deck lead to the formation of settlement trough and surface heaving, frequently creating a bump at the bridge approach and increasing the lateral earth pressure behind the abutment. Measures to reduce the bump at the bridge approach, including several treatment methods, such as compaction of selected backfill materials, grout injection, installation of approach slab, and using a layer of compressible inclusion material behind the abutment were proposed. However, these guidelines still lack sufficient design details and there are limited experimental findings to validate design assumptions. In this paper, the use of engineered compressible materials to alleviate the lateral earth pressure ratcheting and settlement at the bridge approach is investigated. The comparative study is presented for the soil-inclusion, material-structure and soil-structure interactions for an integral bridge under three different backfill conditions, i.e. (a) sand, (b) sand and EPS geofoam, and (c) sand and Infinergy®. The study was conducted in a special large-scale test chamber with a semi-scale abutment to gain better insights into the soil-structure interaction (SSI). The kinematics and rearrangement of the soil during the cyclic loading have been investigated to identify the mitigating effects of compressible inclusions. The comparative study indicates that both compressible inclusions perform comparatively well, however, Infinergy® is a better alternative than the medium-density EPS geofoam, as it works more effectively to reduce the backfill settlement and heaving as well as soil ratcheting effects under cyclic translational movement.

Keywords

• Integral bridge
• Cyclic loading
• Stress ratcheting
• Settlement bump
• Earth pressure distribution
• Soil-structure interaction (SSI)