Influence of Salt Solutions on the Undrained Shear Strength and the Clogging of Smectite-Quartz Mixtures

Abstract

During mechanical tunnel driving, the excavated material often leads to several problems. For example, the sticking of clay in a tunnel boring machine can occur at various surfaces: at the cutting wheel, in the mixing chamber, and in the transport system. Unfortunately, it is presently very difficult to quantify the adhesion by using laboratory tests. Additionally, methods used to address the clogging are still based on empirical attempts without acting on the mineralogical properties of the clays. Atterberg limit determinations and undrained shear tests were performed in order to observe the variation of these simple mechanical properties for smectite-quartz powder mixtures with water and different electrolytes (e.g., NaCl and CaCl 2 ). Additionally, the clogging potential of pure smectite-quartz powder mixtures with water, NaCl, and CaCl 2 was quantified by the so-called cone pull-out test. NaCl and CaCl 2 solutions reduce the clogging of smectite-quartz mixtures in the laboratory due to a decrease in the liquid limit and plasticity index. This work will help researchers to gain a better understanding of the mechanisms that influence clogging during mechanical tunnel driving in clayey soil sediments, as the effects of different electrolytes on the variation of soil sediment properties.