Criteria for Clogging Potential in Coarse-Grained Strata during Shield Tunneling

Engineering practice has shown that shield machines may become clogged in coarse-grained strata. The criteria for determining the clogging potential in coarse-grained strata were proposed. With the surface area ratio of fine to coarse particles in a soil specimen being > 30:1, the interfacial shear adhesion showed a trend of increasing first and then decreasing with an elevation in water content. However, the interfacial shear adhesion remained negligible for the soil specimen with a surface area ratio of fine to coarse particles < 25:1. Interfacial shear adhesion could be adopted for characterizing the risk of shield clogging. Thus, a critical surface area ratio of 25:1 was suggested to evaluate the possibility of clogging in coarse-grained soils. The particle gradation had no effect on the critical surface area ratio with clogging potential. The bound water between the fine particles was released after the injection of the dispersant, resulting in a reduction in the interfacial shear adhesion. The clogging potential of the soil also decreased, while the critical surface area ratio of fine to coarse particles increased.