Large-Flume Observations of Scour at Bridge Abutments with Weak Compacted-Soil Embankment Approaches

Compacted-soil embankment approaches to bridge abutments commonly fail during abutment scour. This paper presents flume observations on scour at bridge abutments with embankment approaches formed of weak, or weakened, compacted soil. The failure modes described in this paper add to modes reported by prior studies and are at one extreme of a range of failure modes insofar that abutment failure is attributable to erosion and washout of a relatively weak or weakened approach rather than the scour of the floodplain near the abutment toe. A prominent observation was that the local flow field around an abutment column, where it adjoined the approach, plays a significant role in eroding the embankment. One experiment with a riprap-protected, spill-through abutment led to the result of scour perched up in the partially eroded compacted-soil approach around an abutment column. The embankment approaches tested were larger than those used in flumes presented heretofore.