A new method to quantify rheology of conditioned soil for application in EPB TBM tunneling

The muck in the excavation chamber and the screw conveyor of Earth Pressure Balance (EPB) TBM, which comprises soil and rock fragments, is often conditioned to adjust its properties for more efficient operation of the machine. The target properties of the conditioned soil include low permeability, high compressibility, proper yield stress and viscosity, and low abrasivity, which are controlled to allow for maintaining face pressure, and facilitate reduced torque and wear of machine components. Among the critical properties, soil rheology plays a major role in offering desired characteristics in the conditioned soil. Measurement and characterization of the rheology of conditioned soil allows for optimizing the conditioning parameters and modeling of the muck flow through the machine. This paper offers a brief review of available testing methods to characterize muck property, with focus on comparison of various soil rheology measurement systems. The main emphasis will be on muck behavior and its impact on operation of soft ground EPB machines. A new device for evaluation of soil rheology under specific settings of the conditioned soil in soft ground tunneling is introduced and the preliminary results of the proposed testing method are discussed. The initial process of optimizing the configuration of the device for higher accuracy and sensitivity to rheological properties of conditioned soil through computational models are explained. The results of numerical modeling using CFD simulation software to identify the preferred configuration of the new soil rheology measurement device will be discussed and the feasibility of using the proposed system for quantification of the soil rheology for tunneling applications is examined.