Abutment Failure During Bridge Waterway Scour

This paper presents preliminary laboratory flume and field observations addressing the basic question-How do bridge abutments actually fail during abutment scour? The observations show that hydraulic and geotechnical processes interactively expose embankment and riverbank material to sequences of hydraulic erosion and geotechnical toppling failure at the abutment waterline, as well as scour of the channel bed or floodplain. Present design and monitoring practicesfor abutments do not address the combination of hydraulic and geotechnical processes that lead to both abutment erosion and failure modes. Also, present design practice for riprap protection of abutments may be inadequate. Consequently, existing abutments remain prone to erosion and failure during abutment scour. Moreover, some countermeasures likely are of limited effectiveness because they address only one of the two failure modes.