Application of colloidal silica in tunnelling

In the construction of tunnels in low-bearing and water-saturated rock masses, grouting is often used as a ground improvement technique. Improvement of rock mass properties prior to excavation is of great importance for excavation stability, reduction of convergence of the excavated contour, shortening of construction time. Various materials are used for grouting purposes: cement-based materials, bentonite emulsions, colloidal silica, and others. In case of water-saturated environments, colloidal silica is most commonly used. The first part of the paper is dealing with the basic characteristics of the material of colloidal silica, with an analysis of its application. The second part of the paper presents an example of the application of colloidal silica in the construction of a railway tunnel in water-saturated rock masses.