GeoCongress 2012

Experimental Assessment of the Passive Resistance of a Bridge Abutment System with Various Backfill Heights


Two full scale lateral load tests were performed on abutment backwall systems 4.57 m wide, 2.8m tall, and 0.91m thick using silty sand backfill with 1.68m and 2.4m heights. The backfill material type and compaction (median of 96% modified Proctor relative compaction) satisfied California bridge design standards. The loading system operates under displacement control and provides horizontal wall displacement with minimal vertical displacement. Wingwalls are furnished with PVC sheets to minimize side friction, providing for 2D plane strain conditions during the experiments. Testing was performed under quasi-static lateral loading up to displacements equal to 10% of the wall height, with unloading and reloading at several displacement levels. In the 1.68 m and 2.4 m tests, peak resistances occurred at horizontal displacements of 0.03H and 0.06H and produced peak passive earth pressure coefficients of 16 and 24, respectively. Following testing, trenching of the backfill material revealed log-spiral shaped principal failure surfaces in both tests along with relatively minor shear surfaces at shallower depths. Results from various analytical models are compared with the experimental results.