Investigation of adhesion of loess to shield’s cutting tools considering sand and clay additives

•The adhesion to cutting tools is evaluated considering sand and clay as additives.•The adhesion is evaluated through a combination of mixing and fluidity tests.•The inherent mechanism is explored by atomic force microscopy analysis.•The intermolecular force dominates the adhesion applied to the sand-loess mixture.•The capillary tension controls the adhesion applied to the clay-loess mixture. Soils, especially those containing a significant fraction of clay, adhering to shields’ cutting tools or clumping to each other could not only cause a low advance rate in tunnel construction but also difficulty in transporting tunnelling spoils for disposal. Although more than 80% silt is regarded as the major fraction, 10% clay also included in loess which is extensively spread over northwest China may aggravate the said issue. In addition to the mixing and fluidity tests, the atomic force microscopy (AFM) analysis was applied to explore the inherent mechanism that affected their adhesion properties when sand, kaolinite, and montmorillonite were introduced as additives. Results showed that the sand additive reduced not only the potential to trigger clay clogging but also the difficulty in transporting spoils for disposal. By contrast, the kaolinite additive increases the potential to trigger clay clogging and also aggravates the difficulty in transporting spoils for disposal. Despite that, the adhesion force was higher in the sand-loess mixture, most likely due to the non-swelling nature of kaolinite minerals. Therefore, the water rings cannot be developed impeding the formation of capillary phenomenon. The adhesion of the sand-loess mixture is controlled by the intermolecular force and rapidly disappears when submerged. Further, the montmorillonite additive increases further the potential to trigger clay clogging but causes great difficulty in transporting spoils for disposal. Results from the AFM test also indicated that the surface topography showed a small change, with the maximum adhesion force being 52.5 nN. The more the water rings developed, the more significant the capillary phenomenon, and the greater the adhesion force.