Competition between rheological degradation and particle clogging in bentonite slurry penetration under seawater intrusion

Seawater intrusion can significantly alter bentonite slurry behavior and affect filter cake formation in slurry shield tunneling. This study investigates the competition between rheological degradation and particle clogging during slurry penetration into saturated sand under saline conditions. Bentonite slurries with salinities of 0%–3.5% were prepared using artificial seawater, and rheological measurements, penetration tests, post-test specimen observations, and SEM analyses were conducted. Increasing salinity markedly reduced slurry rheological resistance while promoting particle aggregation. In fine sand, stable filter cakes formed under all salinity conditions because the small pore throats allowed effective particle retention. However, the filter cakes became more porous under saline conditions, as confirmed by SEM and binarized images. In medium sand, stable filter cake formation was observed at salinities up to 1.0%, whereas failure occurred at 1.5% and above, indicating that particle clogging was insufficient to compensate for the loss of rheological resistance in larger pore channels. These results show that filter cake formation under seawater intrusion is governed by the competition between rheological degradation and particle clogging, providing insight into slurry support degradation in coastal and subsea tunneling.