Nanosilica Grout Permeation in Sand: Experimental Investigation and Modeling

Low-pressure injection of nanosilica aqueous suspensions is often adopted to either waterproof or increase the liquefaction resistance of granular soils. The basic principle behind this ground improvement technique consists in filling the soil pores with a low-viscosity fluid that changes its consistency with time, first into a gel, then into a solid. From an application point of view, the simulation of the time-dependent permeation process is crucial to relate the in situ distance covered by the grout to the operational parameters. A comprehensive investigation was performed, combining laboratory experiments with theoretical approaches, to characterize the phenomenon and then derive predictive relations useful for designing treatment executions. The time-dependent rheological properties of different nanosilica aqueous suspensions were first quantified by means of rheometric tests, then described with Bingham's law. Grout permeation in granular media was then simulated by suitably modifying Darcy's law to incorporate the temporal evolution of Binghamian grout rheology. After validating the modified Darcy's law employment for nanosilica grout flows with respect to laboratory experimental data, simplified analytical equations, capable of predicting the temporal evolution of the distance covered in situ by the grout and the flow rate-injection pressure relation, are provided.