When boring a tunnel with a tunnel boring machine (TBM) through stiff clays, clay tends to stick to the cutting wheel, to the inside of the excavation chamber and in the slurry transportation line. Several solutions are available to prevent the adherence of clay, but these are not always satisfactory. An alternative solution may be the use of electro-osmosis. By applying an electric charge to the steel parts of a TBM, water can be transported through the clay by electro-osmosis to the interface between the clay and the steel. This creates a film of water at the clay-steel interface and therefore reduces the adherence. Because of this film, the hydraulic force of the slurry can easily remove the clay. To investigate the effect of electro-osmosis on clay adherence, laboratory tests were performed on four different clay soils using two test methods, the tilted plate and the direct shear box. It is shown that both tests can be used to reveal the sensitivity of a clay soil to a reduction in the adherence by electro-osmosis. Apart from a so-called threshold potential below which little reduction in adherence is observed, the shear box test allows the determination of the shear stress drop due to electro-osmosis. Finally, a feasibility study is carried out in order to investigate the applicability of electro-osmosis to reduce the adherence inside a TBM. This depends on three factors: properties of the excavated clay soil, practical limitations or negative side effects and the energy consumption.@en