Report 290 Innovative structural backfills to integral bridge abutments

Publication Year

1997

Document Status

Current

Abstract

Investigations have confirmed that most bridge deck expansion joints leak and contribute more than any other factor to deck and substructure corrosion from de-icing salts. For this reason joint-free integral bridges, with the abutments structurally connected to a continuous deck, are more durable and cheaper to maintain. However, thermal strains in an integral deck cause cyclic loading on the soil behind the abutments which may result in the development of passive soil pressures. Traditionally, thorough compaction of high quality granular backfill has been used behind bridge abutments to avoid problems associated with settlement of the backfill and carriageway. In an integral bridge situation however, better quality backfill accentuates the risk of high passive pressures developing. Integral bridge design has therefore to either accommodate or avoid the high forces and moments in the structure that may be generated by the abutment moving into the backfill. One method of avoiding the development of high lateral pressures on the abutment is to use a low stiffness but compressible elastic cushioning layer. This, in turn, would allow a more economical design for the construction of new integral bridges. In addition the method may also provide an economical conversion of existing conventional bridges into integral structures as part of the need to reduce long-term maintenance costs. This report has identified the loading requirements which will need to be met when using a stress absorbing layer behind an integral bridge abutment. Various compressible materials, for example polymeric and geocomposite materials, which may be suitable for use as innovative structural backfill behind integral bridge abutments have been investigated.

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