ABSTRACT
Clogging in tunnel boring machines, particularly in clayey soil layers, is a prevalent problem that could result in decreasing excavation efficiency and elevated project costs. Since clogging is a result of soil adhesion, a comprehensive understanding of this phenomenon is crucial in efforts to mitigate its occurrence. This paper presents the results of pull-out tests for the adhesion characteristics of natural and artificial clayey soils to consider the impact of compositional factors, including clay fraction and mineralogy. The results demonstrate that increasing clay fraction results in a linear increase in adhesion stress, owing to the larger real contact area at the interface between the soil particles and metal, and the results of which were explained theoretically from the mechanism for soil adhesion. The inclusion of montmorillonite led to a significant increase in soil adhesion, due to its distinctive microstructural properties. A revised semi-empirical diagram is proposed, which enables qualitative evaluation of compositional factors on clogging potential. The maximum adhesion stresses measured in the studied samples fall within the region of strong clogging in the semi-empirical diagram, thereby suggesting the feasibility of using adhesion stress as an indicator for clogging assessment.
