The behaviour of soil behind full-height integral abutments

Abstract

Compared with conventional bridges, integral bridges have no bearings or joints between the decks and abutments, thus they can significantly reduce maintenance requirements and costs over the bridge life-time.  The use of integral bridges has been encouraged over the past decade in the UK.  However, because of the integral connection between thee superstructure and the abutments, the integral abutments are forced to move with the deck length change caused by daily and annual variations in the effective bridge temperature.  As a consequence, the soil behind the abutment is subjected to temperature-induced cyclic loading from the abutment, and uncertainties have arisen about the ultimate magnitude of the lateral earth pressure behind integral abutments.

To predict the lateral earth pressure behind integral abutments, a thorough understanding of the soil behaviour is essential.  This research investigated the behaviour of a representative soil element at mid retained height under temperature-induced cyclic loading behind two typical types of full-height integral abutments.  One is an embodied abutment constructed in in situ clayey ground, and the other is a frame abutment backfilled with granular material.  An automated triaxial cyclic loading system has been developed.  Undistributed Atherfield I Clay, Leighton Buzzard B sand and glass ballotini specimens have been subjected to the stress paths and levels of cyclic straining that a typical integral bridge abutment might impose on its retained soil.  The results show that for stiff clay no lateral stress increase was observed, and the stress-strain behaviour and stiffness behaviour were not influenced by cycling.  However, the coarse sand specimens experienced systematic increases in lateral stress for almost all cyclic strain levels, eventually reaching states of stress close to both active and passive.  The underlying mechanisms of stress increase are explored, and it is concluded that particle shape is an important factor in determining the response of soil to this special type of loading.  The implications for integral abutment design have been discussed.

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