Coupled Computational Simulation of Excavation and Soil Transport in Earth-Pressure Balance Shield Tunneling Machines Using a Viscous Two-Phase Fluid Model for Soil-Foam Mixtures
The excavation process ofearth-pressure balance (EPB) shield machines involves the cutting of the ground at the tunnel face and the transport of the soil paste in the excavation chamber. For the numerical simulation of these two processes, a computational strategy, characterized by the coupling of two partial models using the discrete element method (DEM) and the finite element method (FEM) has been developed (Wessels et al., 2013). Excavation is simulated using DEM, with the fracture process being represented by the release of interaction forces between the particles. The transport of the excavated soil mixed with the soil conditioning foam, yielding a pasty soil-foam mixture within the pressure chamber, is simulated by means of a two-phase fluid model in Eulerian description. The two momentum and mixture mass equations are discretized in time by the characteristic-based split method (CBS) (Zienkiewicz et al., 2005). The phase volume fraction equations are solved using upwind weighting functions according to the improved Mizukami-Hughes method (Knobloch, 2006). The proposed model is applied to a coupled analysis of the excavation and transport-mixing flow inside a simplified pressure chamber with foam injections. The mixing process, due to the rotation in the chamber, is preliminarily investigated by the mixing flow in a 2D cavity test case.
Keywords: DEM, Discrete Element Method, Simulation, FEM, Tunneling, Soil-Foam Mixtures, Viscous, Fluid Model