Permeation grouting of an upstream tailing dam: a feasibility study

The presence of potentially liquefiable deposits in tailing dams represents a serious hazard, as is now increasingly clear that liquefaction triggering may occur in unanticipated ways. For legacy dams in which this hazard is already present, intervention alternatives are sought to mitigate the associated risks of liquefaction failure. One interesting possibility is to use targeted ground improvements of tailings within the structural zone of the dams, so that they become nonliquefiable. Liquefaction remediation technologies that are relatively gentle would be preferable, as the possibility of triggering liquefaction during the ground improvement operation itself cannot be lightly discarded. Permeation grouting is a classical soil improvement technology that has been renovated with the apparition of new permeating agents, such as colloidal silica suspensions (CS). Permeation grouting of CS consists in low-pressure injections leading to CS treated soils characterized by a significantly reduced liquefaction potential. CS grout has a complex rheology that is best described by a Bingham model whose parameters change in time. This paper presents design tools that incorporate this complexity and allow both a safer and more realistic design of permeation treatments. As an application example, we study a case based on the Merriespruit tailing dam, which failed by static liquefaction. It is concluded that CS permeation could realistically offer a potential solution to reduce instability risk of some tailing storage facilities (TSF).