Numerical Analysis of the Cofferdam Partial Collapse that Occurred during its Construction

Building the bridge pier foundation for the Bratislava motorway bypass in Slovakia required the construction of a cofferdam in the Danube River. During construction, a local failure occurred, and its cause had to be investigated. In addition to significant cracks on the inner surface of the cofferdam, one of the struts tore away from the sheet pile wall. In this case, the construction process was not carried out in accordance with the project documentation. The project considered creating a stone backfill from the outside of the cofferdam before filling it with soil. However, the stone backfill was constructed only after the cofferdam had been filled to approximately 50% of its height, and its thickness was also insufficient. As a result, the deformations and bending moments in the sheet piles increased significantly, as did the axial forces in the tension bars and struts. Numerical modeling was used to analyze the cofferdam failure. The numerical analysis showed that the ultimate limit state requirements were not satisfied, even for the original design. An alternative solution was proposed by simply modifying the geometry of the stone backfill, demonstrating that all ultimate limit state requirements could be satisfied.