CENTRIFUGE AND ANALYTICAL STUDIES OF FULL HEIGHT BRIDGE ABUTMENT ON PILED FOUNDATION SUBJECTED TO LATERAL LOADING

The objective of this report is to review the current design calculation procedures described in the previous TRL Contractor Report 196 for the design of full-height pile bridge abutments. This review has been based on two subsequent centrifuge model tests, which modelled an 8m full-height piled bridge abutment constructed on a 6m deep soft clay layer overlying a stiff sand substratum. The construction of an embankment adjacent to a full-height piled bridge abutment influences lateral loading on the piles in a number of ways. Firstly, lateral pressure applied to the abutment wall due to placement of the fill will result in a net lateral load which must be resisted by the pile group. Such a mechanism of loading would be considered in any routine design. Secondly, the embankment will act as a surcharge, causing the underlying soft soil to deform laterally, and load the piles directly as it moves past them. Such loading was the subject of the TRL Contractor Report 196. Finally, as the soft clay deforms laterally underneath the embankment, shear stress transfer will occur at the soil-embankment interface. Although such action tends to reduce the lateral soil movement, it does so at the expense of increasing the lateral earth pressure in the lower regions of the embankment. This increase in lateral loading is ultimately transmitted to the pile group as an increase in lateral earth pressure in the fill acting on the abutment wall. The current design calculation procedures using SIMPLE are insufficient to predict this complex soil-structure interaction problem, particularly for shear stress transfer at the soil-embankment interface, effects of pile group rotation and consolidation of the soft soil layer. A revised semi-empirical design calculation procedure is tentatively suggested for the design of piled full-height bridge abutments which have similar structural and foundation characteristics to the centrifuge model tests considered in this report. The procedure is illustrated by a worked example which back-analyses the two centrifuge tests. (A)

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