To investigate the passive force-displacement relationships provided by a transitional zoned backfill consisting of cement treated aggregate (CTA) and compacted gravel, a series of full-scale lateral abutment load tests were performed. The transitional zoned backfill was designed to minimize differential settlement adjacent to bridge abutments for the California High Speed Rail project. Tests were performed with a 2-D or plane strain backfill geometry to simulate a wide abutment. To investigate the effect of skew angle on the passive force, lateral abutment load tests were also performed with a simulated abutment with skew angles of 30º and 45º. The peak passive force developed was about 2.5 times higher than that predicted with the California HSR design method for granular backfill material with a comparable backwall height and width. The displacement required to develop the peak passive force decreased with skew angle and was somewhat less than for conventional granular backfills. Peak passive force developed with displacements of 3 to 1.8% of the wall height, H in comparison to 3 to 5% of H for conventional granular backfills.The skew angle had less effect on the peak passive force for the transitional backfill than for conventional granular backfills. For example, the passive force reduction factor, Rskew, was only 0.83 and 0.51 for the 30º and 45º skew abutments in comparison to 0.51 and 0.37 for conventional granular backfills. Field measurements suggest that the CTA backfill largely moves with the abutment and does not experience significant heave while shear failure and heaving largely occurs in the granular backfill behind the CTA backfill zone.



College and Department

Ira A. Fulton College of Engineering and Technology; Civil and Environmental Engineering

Date Submitted


Document Type





bridge abutment, bridge embankment, cement treatment, full-scale testing, high-speed rail, passive strength, plate-load test, skew, skew reduction factor, transitional zone