Filter cake behaviors in sandy strata: From macro-parameters to pore structure

The slurry infiltration process plays a critical role in slurry shield tunneling, especially in sandy strata. This research investigates the pressure infiltration behaviors of bentonite slurry using a series of slurry infiltration column tests with emphasis on the impacts of pore structures of sand strata on the morphology and mechanical properties of the filter cakes. Average porosities ranging from 0.37 to 0.44 of sand columns were obtained using four types of sand materials. By changing the slurry concentration and infiltration pressure, five types of filter cakes were identified and corresponding pressure infiltration behaviors were characterized. The influences of slurry concentration, infiltration pressure and packing state of sand column on the filter cake performance were analyzed using the permeability of composite soil-cake ( k c ), pressure transmission efficiency ( P t ) and formation time ( t c ). The findings highlighted the controlling role of pore structure of sand strata on the filter cake properties. Linear relationships were established between log 10 k c and representative pore diameter of the sand strata ( d p ) at slurry concentrations of 12%, 16%, and 20% with R 2 = 0.83, 0.81, 0.90, respectively. Furthermore, a critical pore size was found to determine the pressure infiltration characteristics of the filter cake.