A Shear-Slip Mesh Update - Immersed Boundary Finite Element model for computational simulations of material transport in EPB tunnel boring machines

Earth Pressure Balance (EPB) machines are widely used in mechanized tunneling operations in soft soils in a variety of soil conditions. In contrast to slurry shield machines, the pressure distribution at the tunnel face is not well defined. This paper proposes a computational model for the numerical simulation of the material transport inside the pressure chamber of EPB machines. The governing equations of the soil flow are discretized by using the Finite Element (FE) method and the Fractional Step (FS) scheme. A pressure-dependent viscoplastic fluid is adopted to model the behavior of the soil paste, which is assumed to be a compressible homogeneous mixture. The flow behavior along the boundaries of the chamber wall and the cutterhead rotators is described by the Navier slip law. The moving boundaries associated with the rotators and the mixing arms inside the pressure chamber are imposed in the numerical model by means of the Shear-Slip Mesh Update (SSMU) method. The description of the rotating screw in the conveyor system is enabled by using the Immersed Boundary (IB) method. The combination of the two methods enables to exploit the advantages and to mutually compensate for the disadvantages associated with each of the two methods. The numerical components in the model are presented and verified by several numerical benchmark examples. The setup for the chamber model is presented in detail. Selected results from the simulation of a pressure chamber of a tunnel boring machine are shown and some important observations and remarks are discussed.