During the construction of a station of the north south line in Amsterdam a leak in the diaphragm wall lead to severe damage to adjacent buildings. The leak consisted of a clay deposit caught near the joint. Until the excavation reached the level of the deposit, the deposit acted as a seal. After the excavation it started to leak and eventually failed. The following investigation let to no clear explanation of the presence of the deposit. Yet it revealed a lack of a clear understanding of the mechanisms. This prompted an investigation in to these mechanisms. This report deals with the aspect of the flow patterns of the concrete. To investigate the flow pattern of concrete a numerical model has been used. A two dimensional model was created. In the model a constant stream of concrete was introduced in a layer of concrete submerged in a bentonite suspension. With this model a series of simulations are made. The first series is made with a varying yield stress of the bentonite suspension and the concrete. A second series is made with varying yield stress and the density of the bentonite suspension. Finally two simulations were made with varying spacing of the reinforcement bars.