Parameters regulating groundwater inflows into hard rock tunnels—a statistical study of the Bolmen tunnel in Southern Sweden

Abstract

Inflow of groundwater into tunnels has always been a major technical and environmental problem for underground constructions. Predictions of groundwater inflow using analytical and numerical tools have often failed due to generalization and simplification of important parameters, especially in heterogeneous media such as crystalline rocks. In order to identify those parameters that regulate inflows, a systematic statistical analysis has been carried out at a tunnel constructed in the hard crystalline rocks of southern Sweden. The parameters included topographically, technically and geologically important variables in the hard crystalline rocks as well as in the overburden. The study revealed that many factors related to the rock quality, as well as to the overburden—such as the number of fractures, the thickness of the overburden, the soil type and the amount of pregrouting—regulated the leakage. It seems that a clear difference exists between the parameters that regulate the major and the minor leakage. The minor leakage is associated more with the drainage of the rock mass, while the major leakage is clearly associated with different parameters in the overburden. Unless the overburden and the rock mass are considered as an interrelated system, predictions of groundwater inflows are likely to fail.