Cellular cofferdams are increasingly being used as permanent retaining walls, navigation or breakwater structures. When used as breakwaters, the metal fatigue can become a possible mode of failure for cellular structures due to the cyclic unbalanced lateral loads imposed by the wave action;This study was initiated as an investigation of the cell failures of the Calumet Harbor Breakwater structure in the South Chicago Harbor. The primary objective was the assessment of the interlock force fluctuations in the sheetpiles induced by the wave action on the structure;It has been well established that the conventional design methods for cellular structures have substantial shortcomings. These methods are usually overconservative and incapable of predicting deformations. In the past 15 years finite element method has been applied to analyze the cellular structures. The method provides the means to deal with soil-structure interaction problem, loading and geometric irregularities, as well as behavioral complexities of the materials. Past finite element work consisted of two-dimensional model versions. Each of these models require certain assumptions and simplifications regarding loads and geometry and can provide only specific information. Three-dimensional modelling can eliminate these drawbacks at the cost of complex and tedious modelling work and considerable increases in computation time and memory requirements;The Calumet Harbor Breakwater structure was analyzed using two-dimensional vertical slide and three-dimensional finite element models in parallel to evaluate the performances on a comparative basis. The analysis consisted of three main sequential stages: (1) simulation of the construction, (2) simulation of the permanent cumulative wave load effects on the structural condition of the breakwater, (3) wave load analysis;The analysis results showed that the model predictions regarding the interlock forces, displacements and lateral pressures were consistent in the construction simulation stage. However, the differences became more predominant under the increased loading in the second and third stages. In the second stage, the analysis results confirmed that the permanent effects of the wave loads alter the structural state of the breakwater considerably. Regarding the wave load analysis, three-dimensional model predictions resulted in a better agreement with the field recorded data.