Slurry Shield Tunnel Boring Machines (SS-TBM) are soil machines widely employed for underground excavation in urban environments, where excavation at shallow depths in soft, unconsolidated and water bearing-soil, poses major challenges related to face stability and ground settlement. These machines use a bentonite-based slurry to maintain counter pressure, prevent groundwater inflow, and ensure the stability of the excavation face. However, the rheological properties of bentonite slurries can be significantly affected by mechanical degradation during excavation, which may lead to viscosity reduction, problems in pressure transmission and filter cake formation, potentially leading to face instability or slurry losses. This research investigates the rheological behavior of eight different bentonites, used to prepare slurries at varying concentrations, subjected to controlled mechanical stress in order to simulate, at laboratory scale, the stresses experienced by bentonite during SS-TBM excavation.