Prediction of groutability from grout properties and hydrogeological data

Sealing tunnels and caverns in fractured crystalline rocks has been considered notoriously unpredictable and possible to manage only through experience and intuitive knowledge. Words such as “witchcraft” and “black art” have been used ironically in Sweden to describe the state of the art. In this paper, initially grout penetration and grout take in parallell planar fractures are discussed. General expressions for these entities are also derived for fractures with varying width. In this paper, the grout take of a system of inhomogeneous channels in a fracture plane is studied further and the grout takes of such systems are modelled numerically. Grout takes are calculated for increased variability of the fracture aperture and the influence of this is assessed. In normal Swedish grouting procedures, the grouting boreholes are tested by water pressure tests (WPT). The hydrogeological information from these tests can be transferred to grouting apertures, and thus yield design information for grouting operations. Finally, the applicability of the findings is evaluated using field data from grouting of the access tunnel of the Äspö Hard Rock Laboratory, Sweden. The conclusion is that field methods for prediction and design of grouting operations can successfully be based on the theory.