In this paper, an investigation into the causes of measured deformations of a quay wall in the Port of Rotterdam is described. Measurements show that horizontal displacements of the combi wall in seaward direction, increasing nonlinearly in time. This trend was the reason for an investigation into all possible causes of the horizontal displacements on top of the quay wall. The main part of the investigation was elaborated by considering the different influences for a representative cross section by simulating the real soil behaviour with analytical and numerical methods. Examples of effects that have been analysed are time dependent soil behaviour, anchor wall capacity, the influence of expected values in stead of a design philosophy, the influence of the position and magnitude of a surcharge load and accumulating effects of cyclic loading.