Grouting of cohesionless soils by means of colloidal nanosilica

Colloidal nanosilica is an innovative grouting material, currently used in tunnelling applications for grouting fine cohesionless soils when environmental limits prevent the application of other solutions. Despite a large number of applications, knowledge of operational parameters for grouting such as gelling time and dynamic viscosity is very limited. Furthermore, the influence of the type of nanosilica (in terms of SiO2 concentration) and accelerators on the achievable mechanical performance of injected soils has never been investigated. In this work, a laboratory test campaign based on two commercial colloidal nanosilica and two accelerators was conducted. Once the operational parameters had been investigated, four different soils have been grouted and, after curing, mechanically tested. The results, in terms of gelling time and viscosity order of magnitude, are crucial for the correct functioning of a grouting. Furthermore, the results of the uniaxial compression tests, the indirect tensile tests and the direct shear tests have shed light on the potential of colloidal nanosilica and on the differences between the chemicals.