An investigation into development of Smart Integral Bridge and Abutment Designs

Lead Research Organisation: University of Cambridge
Department Name: Engineering

Abstract

The use of integral bridges with a combined bridge deck and abutment walls has been in use for many decades. However their current design is largely based on PD6694 guidelines, which involves a significant amount of empiricism and uncertainty. This is largely due to the unknown stress state and the stress-strain behaviour of the backfill soil behind the abutment walls. The designs can get more conservative with an increase in the span of the bridges. It is also worth noting that older bridges that have bearings can cease up and act like an integral bridge during later years of their service, applying similar loads on the abutment walls and the soil backfill behind these. There is a well-recognised need to reduce the carbon footprint of bridges while delivering a sustainable and resilient highway infrastructure that is robust under climate change. This proposal is aimed at investigating the integral bridge and abutment design with the ultimate aim of improving the design, reduce maintenance and increase the inspection intervals with suitable deployment of smart instrumentation during the construction of these bridges. With this view, the research proposal is divided into three interdependent phases.
Phase I: Deployment of smart instrumentation during bridge construction: In this phase the stakeholders such as the bridge owners, designers, contractors, Highways England, the academics and the research staff are brought together to design the deployment of smart instrumentation that can help with monitoring of thermal expansion of decks, bending moments and shear forces on the deck-abutment wall joints, earth pressures behind the abutment wall, strains mobilised in the backfill soil etc. The selected bridges with this smart instrumentation will be monitored over a long period of 5 to 10 years and will involve many thermal cycles.
Phase II: Development of physical and numerical modelling: Simplified physical models of the integral bridges and the backfill that are highly instrumented will be developed and tested in the large 10m diameter beam centrifuge at Cambridge. Soil strains in the backfill will be recorded directly using high
resolution imaging and use of the geo-PIV software. It is planned that about 5 to 6 centrifuge models will be tested varying the backfill soils, use of geo-foam blocks behind the abutment wall etc. The cost of the centrifuge testing is estimated at about £6k per test. The centrifuge data will be compared to field data, flowing from Phase I of the project at appropriate intervals. In addition, numerical modelling using the finite element method will be carried out and these models will be calibrated against the centrifuge test data. Also the results from the calibrated FE analyses will be compared to field monitoring data flowing from Phase I.
Phase III: Development of design guidelines: In this phase the validity of the current design guidelines is verified. With the view of minimising the carbon footprint and producing a resilient bridge structure that can cope with climate change concerns, the guidelines will be updated for use in future integral bridge design. It is also anticipated that use of more carefully chosen backfill materials with use of geofoams or geo-grids, the designs can be further optimised to minimise the abutment wall movement inducing large strains in the backfill. The possibility of using an optimal thickness of these geo-synthetic material sections to reduce soil strains and any subsequent soil deformation will be investigated.

Publications

10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S02302X/1 01/10/2019 31/03/2028
2439660 Studentship EP/S02302X/1 01/10/2020 30/09/2024 Douglas Morley