Investigation of microfine cement both rheological properties and permeation in soils

Permeation grouting, i.e. injections at low pressure, of microfine cements is frequently adopted in tunnelling and underground structures to either increase the mechanical properties or reduce the hydraulic conductivity of soils. From an applicative point of view, the time dependent permeation process, crucial to assess the spatial contour of the final content of the injected microfine cement, is highly affected not only by operational parameters, geometry of injection sources and particulate phase nature of the grout under exam, but also by its timedependent rheological properties. This latter aspect is not deeply investigated in literature, especially in the ranges of shear rates, times and water-cement ratios commonly adopted during permeation grouting treatments. To this aim, in this paper, a comprehensive investigation has been performed, combining laboratory experiments with theoretical approaches. The time-dependent rheological properties of microfine cements characterized by different water-cement ratios have been first quantified by means of rheometric tests and described with a Bingham's law. The microfine cement permeation in granular media has then been experimentally investigated and so the employment of a Darcy's law modified to incorporate the temporal evolution of Binghamian grout rheologies has been validated for microfine cement flows.