Coupled DEM-FDM numerical model for EPB shield tunnelling simulation with foam conditioning

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It is widely recognized that an appropriate application of soil conditioning significantly improves the tunnelling performance of earth pressure balance (EPB) shield tunnel boring machines (TBMs). This study presents a numerical approach that simulates an EPB shield tunnelling, considering the injection of foam into the soil. To enhance computational efficiency and reduce the number of particles simulated in the ground formation, the numerical study coupled the discrete element method (DEM) and the finite difference method (FDM). The properties of in-situ soil and foam-conditioned soil were incorporated into the DEM domain by determining the contact parameters of particles using two calibration models: the triaxial compression test and the pressurized vane shear test models. With the established model, tunnelling analyses were conducted under specific TBM operation conditions, such as the penetration rate, and rotational speed of the cutter head and the screw conveyor. The effect of foam injection on EPB shield TBM operation was evaluated by adjusting the contact parameters of DEM elements. The numerical simulations revealed that foam conditioning reduced the torque, thrust force, and forces on cutting tools. These simulations provided valuable insights into the applicability of the numerical approach in assessing foam conditioning for EPB shield TBMs.