Comprehensive loess soil adhesion properties assessment: Insights from laboratory tests and atomic scale analyses

During tunnel excavation, 'clogging', induced by sticky material, often occurs at the cutting face through to separation and transport for disposal, causing unplanned downtimes and additional project costs. However, past studies have mainly focused on the clayey soils' clogging properties, and there is a pressing need of studying the clogging potential of mixtures containing the majority of silt soil while tunnelling in North-West China. In this study, the effect of the proportion of particles in different sizes on the adhesion, fluidity, and consistency of the additivesilt mixtures was investigated. The effect of sand and clay addition on the adhesion force and fluidity was explored. Sand has a good viscosity reduction effect on low plastic silt, and adding sand will significantly reduce adhesion and increase fluidity. The addition of clayey clays (kaolinite and bentonite) to silt has a certain adherence reduction effect. The former reduces the risk of clogging due to the more content of non-expansion of kaolinite, while the latter is due to the fact that a large fraction of bentonite increases the liquid-plastic limit of the soil mixture and increases the water film thickness, resulting in the reduction of adhesion ratio. The variation of the soil consistency against the additive fraction was opposite to the variation of the maximum adhesion ratio. The findings highlight the role of additives in reducing the adhesion forces and the importance of cutting off the provision of additional water in preventing the sticky material transformation.