Reduction of the clogging potential of clays: new chemical applications and novel quantification approaches

Earth pressure balance machines are increasingly being used for tunnelling in difficult soils and ground conditions. In clayey soils, clogging of the working tools is among the main hazards. Attempts to reduce this risk by adding anti-clogging chemicals do not always produce the desired effect. In this paper, the limited efficiency of the existing conditioning chemicals is quantified and explained, and an enhanced interaction mechanism is proposed. This mechanism is based on sealing the clay aggregates against the penetration of water; it requires the addition of polyamine chemicals, as a newly patented application. These chemicals have been shown to dramatically reduce the clogging potential of different clay pastes over a broad range of water contents, using novel approaches for quantifying the clogging behaviour of clays in general. These methods also establish important correlations between empirical stickiness and more fundamental soil parameters, and in particular the ratio between adhesion and strength. Together with microscopic investigations and adsorption measurements, this provides insight into the working mechanism of the new chemicals at the particle level; it also highlights the differences between this mechanism and that of commercially used foams and polymers.