Low permeable soil is important for stabilising the tunnel face during mechanized tunnelling
in sandy soils under water level. Foam is one of the most common conditioning agents to
achieve low permeability of the excavated soil. This study investigates the effect of hydraulic
gradient on the permeability characteristics of foam-conditioned sand in various conditioning
states, according to a series of experimental permeability tests under different hydraulic
gradients. With an increase in the hydraulic gradient, the duration of the initial stable stage of …