A strength-based clogging risk assessment strategy for mechanized tunneling

The adhesion strength of muck is a crucial factor influencing Earth Pressure Balance (EPB) shield clogging, but this perspective overlooks the role of muck’s shear strength. Therefore, it is crucial to comprehensively evaluate the risk of shield clogging based on muck strength. Adhesion strength and triaxial tests were conducted on the moderately weathered mudstone muck using a rotary shear apparatus and a soil-shape-controlled triaxial device. This work explores the relationship between tangential adhesion strength (referred to as adhesion strength) and shear strength of moderately weathered mudstone muck. The adhesion strength and the shear strength exhibited similar variation patterns. As the consistency index increased, the adhesion strength of the muck gradually rose. The interfacial friction angle increased, while the interfacial adhesion force initially rose before declining. The adhesion and shear strengths of muck can be assessed by integrating the effects of stratigraphic stress. When the adhesion strength surpasses the shear strength, the shield faces a risk of muck adhesion. Building on this insight, a strength-based clogging risk assessment strategy for mechanized tunneling was proposed. Field tests demonstrated that the risk assessment strategy effectively evaluated the potential for shield clogging both before and after dispersant treatment, thereby ensuring the safety and efficiency of shield tunneling. Moreover, recognizing the influence of temperature, consolidation, and critical shear strength on the potential for shield clogging, the authors will continue to focus on these factors in future work.