Case Study Comparing Embodied Carbon Emissions in Two Road-Over-Rail Bridge Foundation Designs

This paper examines and compares the embodied carbon emissions in the earthworks and foundation design for two road- over-rail integral bridges as part of a project in Western Australia. The first bridge is supported on gravity footings and constructed using bottom-up methods, the second on load-bearing contiguous piles and constructed using top-down methods. The abutments support a cut profile of sand and limestone up to 10 m high.

A Life Cycle Assessment (LCA) for embodied carbon emissions was carried out for each bridge using the framework of PAS 2080. Construction-stage design information was used in the assessment, representing a bottom-up LCA approach to retrospectively identify carbon hotspots to inform future designs.

The assessment incorporated geotechnical site investigations; temporary works; bulk excavation for gravity footings and other minor excavations; and the raw materials for construction of the two foundation types. Transportation of materials to site, construction processes and final deconstruction and disposal of the structures were also considered. The bridge superstructure was outside the scope of the assessment.

The results are presented in total tonne CO2e per bridge and tonne CO2e per bridge deck area to allow direct comparison of the embodied carbon emissions of the two bridge foundation systems. The carbon hotspots in each design are identified, and the authors discuss how the results can be communicated to clients and contractors to be weighed alongside the various other drivers that influence construction method and design.

The paper closes with the authors’ assessment of opportunities across the design process where geotechnical designers have most influence on embodied carbon over the design life of these bridge types.