Permeability characteristics of coarse-grained soil conditioned with foam for EPB shield tunnelling

Abstract

Foam is often used to reduce the permeability coefficient of coarse-grained soil to avoid water spewing during earth pressure balance (EPB) shield tunnelling. A series of permeability tests were carried out on foam-conditioned soil. The test results show that with an increase in d10, the initial permeability coefficient of the conditioned soil increased greatly, however, it only changed slightly with increases in Cc and Cu. In addition, permeability coefficient was much lower than that of the unconditioned soil, even though the slow growth period had been entered for a long time. The results also indicate that d10 greatly affected the permeability characteristics of conditioned soil. By contrast, Cc and Cu had less effects. In addition, it is not reasonable to consider that the permeability coefficient of the conditioned soil will reach or be close to that of unconditioned soil when most, or all, of foam in the foam-conditioned soil dissipates.