State-of-the-art review on pressure infiltration behavior of bentonite slurry into saturated sand for TBM tunneling

Abstract The pressure infiltration behavior of bentonite slurry (a mixture of water and bentonite) in front of a slurry tunnel boring machine (TBM) determines the effectiveness of tunnel face support when tunneling through saturated sand. This paper provides a comprehensive review of relevant studies, encompassing the rheology of bentonite slurry, laboratory experiments, numerical simulations for modeling slurry infiltration in sand, and an exploration of the membrane behavior of filter cake. The review found that variations in test conditions for bentonite slurry are the primary contributing factor leading to discrepancies in rheological measurement results. Conventional column-based slurry infiltration tests often impose a high hydraulic gradient on the soil sample, making the observations from these tests incomparable to real tunnel scenarios where the hydraulic gradient is much lower. Two primary slurry infiltration types were identified: one involving an external filter cake alongside an infiltration zone, and the other featuring solely an infiltration zone. The filter cake effectively stops further infiltration of bentonite and serves as a media for transferring the slurry pressure to the soil skeleton. Owing to the viscoplastic properties of bentonite slurry, a decrease in flow velocity fosters an increase in rheological resistance, thereby aiding in the stabilization of the excavation process. The inclusion of fine sand, seawater, and liquids with acidic or heavy metal properties could notably undermine both the characteristics of bentonite slurry and the sealing capacity of the filter cake. Hence, it becomes crucial to effectively control the workability of bentonite slurry throughout the process of slurry TBM tunneling.