Numerical modeling of grout spread and leakage into a tunnel in hard rock – a case study

SYNOPSIS During tunnel construction in fractured rock, a detailed hydrogeological description of the rock is of importance for successful grouting design and estimating leakage. A common simplification has been to assume the fractures as independent parallel plates; a 2D stacked model. However, analytical inflow predictions based on this model have not been sufficiently accurate. The aim of this work is to study whether a more realistic 3D fracture model, viewing the fracture system as a network of connected fractures, could better explain the sealing effects of grout compared to the 2D model. Inflow into a tunnel and grout penetration have been studied in a three-fracture network model, using the numerical groundwater flow code DarcyTools, version 3.1. Ideas developed from this study were then applied to a real case tunnel. Deviations from the analytical prediction of inflow into the grouted tunnel can be understood, in part at least, by taking the connectivity of the rock volume into account. The results further enhance the importance of firm geological and hydrogeological characterization of the rock mass that needs to be sealed with grout to reach a tolerable inflow of groundwater