Tunnel boring with foamed composition

Abstract

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, characterized in that (a) the aqueous solution contains two essential components which are (i) a sulphate- or sulphonate-containing anionic susfactant, and (ii) β-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 high water content.

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