Port Terminal Anchored Bulkhead Failure: A Forensic Case Study

A 360-ft (110-m) long steel sheet pile anchored bulkhead at a waterfront terminal in Charleston, South Carolina, underwent a sudden failure in 2012. The anchored bulkhead was originally constructed in the 1970s by the US Navy and featured, approximately, a total structure height of 72-ft (22-m) and 61-ft (19-m) long sheet piles. The failure zone extended inland from the waterfront upwards of 190-ft (58-m), and included the bulkhead and concrete relieving platform, landward stormwater drainage culverts and boxes, backfill, aggregate stockpiles, and heavy equipment. Fortunately, despite the large failure zone, there were no casualties as the terminal was in between shifts at the time of the collapse. Insurance claims and subrogation litigation ensued as a result of the failure. The author was retained by insurance interests for the terminal owner to conduct the failure analysis. The analysis included site reconnaissance soon after the failure, review of original design documents, and numerical analysis of several soil-structure profiles. The purpose of the analysis was to determine the most likely mode of failure and to identify pertinent factors of the failure. The mode of failure was determined to be a global structure-slope stability failure from excessive surcharge loads due to aggregate stockpiles behind the bulkhead. An alternative hypothesis was offered by an adverse party that sheet pile toe failure occurred due to dredging in excess of the design depth. This alternative hypothesis was excluded by numerical analysis in correlation with the known field conditions. This paper will review several challenges with investigating such a failure and will discuss several models and variables the investigators considered for the subject analysis.