Evaluating rheology of conditioned soil using commercially available surfactants (foam) for simulation of material flow through EPB machine

Abstract

The number of soft-ground Tunnel Boring Machine (TBM) with an active support pressure has increased significantly around the globe in the past few decades due to the advances in their capabilities and remarkable achievements. Over 90% of these machines are Earth Pressure Balance (EPB) TBMs. The muck in the excavation chamber and the screw conveyor of an EPB machine is often conditioned to modify its properties for improving the operation of the machine, i.e., reduction of the cutterhead and screw conveyor torque, regulation of the face pressure, and efficient mucking. To achieve these goals, the common targeted properties of the conditioned muck include low permeability, high compressibility, low abrasiveness, low stickiness, and proper balance between flow capability and viscosity. Among the various critical properties, soil rheology offers a comprehensive perspective on the desired features of the conditioned muck. This paper reviews the existing soil rheology measurement systems ranging from small-scale rheometers to large-scale screw conveyor models, including review of a macro-scale rheology measurement system recently developed at Colorado School of Mines (CSM). The new optimal propeller geometry suggested by Computational Fluid Dynamics (CFD) simulation was incorporated into the measurement system. Rheological parameters of soil with different soil conditioning and machine operational settings were investigated with the optimized measurement system. The study shows the interdependency between soil conditioning settings and rheological parameters in the modified soil. The measured rheological parameters of conditioned soil can be used in the simulation of muck flow within the excavation chamber and the screw conveyor of an EPB machine by CFD simulation.