A study on the effects of abutment cyclic movements on the approach of integral abutment bridges

Abutments in integral bridges experience rotational cyclic movements as a result of the temperature induced changes in the longitudinal dimension of the bridge deck. Cyclic movements of abutments against and away from the retained backfill result in densification and volume contraction of the soil adjacent to the abutment wall. Consequently, the retained soil will experience settlement in the vicinity of the bridge approach in addition to an increase in the lateral earth pressure exerted on the abutment. The settlement of bridge approaches causes rideability and safety issues for bridge users while the escalated earth pressure may result in structural damage to the bridge abutment in the long term. This paper used the finite element method to investigate an integral abutment wall subjected to cyclic perturbations using the ABAQUS software. Two primary modelling cases were investigated. In Case 1, a finite element model was developed and verified against centrifuge test results of an integral bridge abutment before using it to study various factors influencing the response of the approach backfill subjected to cyclic rotational movement of the abutment. In Case 2, the finite element model was modified to incorporate the use of expanded polystyrene (EPS) geofoam in the approach backfill and it was once again verified against results from a laboratory experimental study. The modified finite element model was applied to study potential solutions using EPS geofoam to mitigate the soil settlement and to prevent the stress ratcheting at the interface between the backfill and the abutment. Results from the finite element study without and with EPS geofoam (Case 1 and Case 2 respectively) in the approach backfill subjected to cyclic rotational movement of the bridge abutment are discussed.