Failure Case Study of Offshore Battered Drilled Shafts Due to Seabed Rock Scouring

The influence of lateral loads in the offshore environment, such as tides and waves, reduces the stability of the piles under construction and during operation. Scour of the seabed caused by the flow around bridge piers also has a strong influence on the stability and the integrity of offshore structures. In this paper, a comprehensive case study on the offshore bridge piers is highlighted. Special attention was given to the investigation of the collapse of three bridge piers during construction caused by extreme lateral load and seabed scour. To obtain detailed information, an intensive study was carried out to analyze the effect of scour on the stability of battered piles during construction, as well as under in-use conditions. An empirical analysis using HEC-18 (hydraulic engineering circular no. 18, FHWA, 2012) for estimating rock scour was performed along with the results from a multi sonar field test, to accurately estimate the scour depth of the seabed. Through empirical analysis, field test, and numerical analysis, it is shown that the seabed rock scour combined with the relatively short embedded length of piles had critical influence on the stability of these offshore pile foundations.