The flow of bentonite and grout around a TBM influences the settlement trough that is created during TBM tunneling. Not taking into account this flow, leads to a calculated settlement trough that is too deep. Two calculation methods have been developed: a 1-D analytical model taking into account the basic aspects of this flow and assuming flow in only one direction and a 3-D numerical model, which also assumes flow in one direction, but considers the calculated width and spatial distribution of the steering gap using a hybrid Finite Element—Finite Difference model. The paper describes briefly both models (making reference to more elaborate descriptions) and compares the results of both models. It will be discussed what are the limits of the analytical model and where the numerical model has to be used.