Electrochemical control of loess adhesion on shield cutting tools

The adhesion of sticky soils to shield cutting tools presents a persistent challenge in urban tunneling, contributing to elevated safety risks and delays in excavation progress. Loess from northwest China demonstrates transitional behavior between clays and poorly graded sands, and, following weathering, releases both cations and anions. The prevalence of alkaline environments in this region further alters the electrochemical properties of loess. This study systematically investigated the electrochemical control of loess adhesion on shield cutting tools through plate sliding, plate pullout, and electroosmotic flow experiments. Results showed that cations with high electrovalency reduced the Debye length, squeezed the diffuse double layer, and decreased the absolute value of electrokinetic potential (below 25 mV). While anions generally reduced both normal and tangential adhesions, the presence of SO4 2- and Na? after ionization unexpectedly increased adhesion by diminishing electrostatic repulsion. Acidic pH conditions similarly reduced the Debye length and absolute value of electrokinetic potential, promoting the formation of a viscous water film and enhancing adhesion at the soil–metal interface. Compared to pure loess, the contact angle decreased by 15 degrees, indicating increased fluid viscosity and reduced capillary tension, which provides evidence for this claim. Electroosmosis was found to be effective in reducing adhesion, except when MgCl2 and AlCl3 additives were present. In these cases, the high electrovalency of the cations reversed surface charges, inducing ‘reversed’ electroosmotic flow and resulting in adhesion values exceeding those observed before treatment. These insights advance the understanding of electrochemical control of loess adhesion on shield cutting tools and further inform the development of effective strategies to mitigate safety risks and delays in tunneling operations.