Soil conditioning technology is commonly applied to prevent mud caking and soil clogging in earth pressure balance (EPB) shield tunneling and to ensure continuous and efficient construction in highly viscous clay and weathered mudstone strata. In the note, the properties of soil conditioning agents and their interactions are investigated through a series of experimental tests and field construction applications in Changchun Metro Line 2, China. Tangential adhesion tests are carried out to learn the adhesion strength and the torque change relationship between the soil and the metal disk, by which the soil conditioning effect is evaluated. The results indicate that there is a certain interaction between the commercial foam agent and the customized anticlay agent and that the foam agent solution’s concentration and anticlay agent amount play an important role in determining the foam expansion ratio (FER) and the half-life time (HT). When the foam agent solution’s concentration is low, the anticlay agent can increase the FER and decrease the HT. When the foam agent solution’s concentration exceeds 4%, an opposite pattern is observed. It is also found that the composite application of an anticlay agent and a foam agent can significantly decrease the torque and adhesion strength of the weathered mudstone. Torque and adhesion strength can reflect the adhesion of chemically conditioned soil better than the consistency index, which has a good effect on the evaluation of unconditioned soil. Finally, field implementation indicates that mud caking and soil clogging were avoided by the application of the two conditioning agents in the EPB shield tunneling construction of Changchun Metro Line 2, China, and the thrust and torque of the shield were reduced.

When a slurry shield tunnel boring machine (TBM) encounters sticky ground during tunneling, mud cakes often occur on the cutter head due to the high stickiness of soil. The mud cakes caused several negative issues, such as high torque demand, advancement rate reduction, and additional costs. Existing studies have largely focused on Earth pressure balance TBMs; research on formation and mitigation measures of mud cakes in slurry shield TBMs is limited. Therefore, this study proposes the addition of dispersant to the slurry to prevent mud cakes during the tunneling of slurry shield TBMs by reducing stickiness of excavated clay. The basic properties of slurry were measured experimentally, and the effectiveness of dispersant in reducing the potential for mud cakes was investigated through mixing tests and viscosity experiments. A statistical analysis of the data was performed to determine relationships between slurry properties and material behaviors. The results showed that the slurry with dispersant had a lower viscosity and formed filter cakes more quickly, thereby meeting the performance requirements of a supporting fluid for slurry shield TBMs. Further, dispersant effectively reduced the empirical stickiness ratio and suspension viscosity. Therefore, a slurry with an appropriate dispersant content could effectively reduce the potential for mud cake formation.

Tunnel Boring Machines (TBMs) are integral to modern underground engineering construction, offering enhanced safety and efficiency. However, TBMs often face challenges in complex geological conditions, such as composite strata, resulting in reduced advancement speed and increased cutter wear. This study investigates the rock-breaking characteristics of TBM disc cutters in composite strata through numerical simulations using the Particle Flow Code (PFC) 5.0 software. Focusing on the Jinan Metro Line 6, the research analyzes cutter forces, rock crack propagation, and the impact of cutter edge shapes on rock-breaking efficiency. The discrete element method (DEM) is employed to simulate microscopic behaviors of rocks, providing insights into crack formation, expansion, and failure. This study’s findings reveal that cutter design and operational parameters can significantly influence cutter lifespan and efficiency. By modifying cutter spacing and penetration depth, enhancing rock-breaking efficiency, and grouting softer layers, TBMs can maintain effective excavation in composite strata. The study establishes a comprehensive understanding of the interplay between TBM cutters and complex geological conditions, offering actionable strategies to enhance TBM performance and mitigate cutter damage.