A process of boring a tunnel using an earth-
pressure balance shield boring tunnelling
machine having a
cutting head, an excavation chamber for soil removed by boring and conveying means for removal of said soil from the excavation chamber; wherein there is injected into a stratum being bored at the
cutting head a foamed
aqueous solution, characterised in that (a) the
aqueous solution contains two essential components which are (i) a sulphate- or sulphonate-containing anionic surfactant, and (ii) beta -
naphthalene sulphonate-
formaldehyde condensate; and in that (b) there is applied to the soil removed by boring in at least one of the excavation chamber and the conveyor a second
aqueous solution containing essentially a high molecular weight
polyethylene oxide and optionally a sulphate- or sulphonate-containing anionic surfactant. The process allows easy removal of soil from the
cutting head to the excavation chamber and from the excavation chamber out of the
machine. It is particularly effective for sticky soils with high proportions of clay and a
high water content.