The flow of muck and cuttings in the face, cutterhead, cutting chamber, and screw conveyor determines the pressure profile of the excavated soil as well as its impact on the wear of the related components in a soft ground tunneling machine. This paper discusses the use of Computational Fluid Dynamic (CFD) to simulate the flow characteristic of the conditioned soil in the screw conveyor of Earth Pressure Balance (EPB) tunnel boring machine. In this simulation, conditioned soil assumed to behavior as a Bingham plastic fluid. Back analysis method in conjunction with CFD modeling is used to calculate the rheological properties of soil from a set of known screw conveyor torque read outs from a machine operating in Seattle, WA. The error of the torque values between the simulation results and actual field data is in the range of 0.1-6.2%. This illustrate that the CFD method can simulate the soil movement in the screw conveyor of EPB machines. The results also indicates that the same approach can be used to optimize the machine design to minimize torque and wear as well as optimizing machine operating parameters during the tunneling operation to improve productivity and have a better control of the face pressure. (C) 2015 Elsevier Ltd. All rights reserved.