Semmering Base Tunnel – Excavation of the emergency station in complex ground conditions

Abstract

At the construction lot SBT 2.1 ”Tunnel Fröschnitzgraben“ of the Semmering Base Tunnel (SBT) in Austria caverns with a cross section up to 300 m2 are excavated in a depth of approximately 400 m, which are the central part of the emergency station. The site arrangement results in a complex situation of large cross sections within a small area. Additionally, complex ground conditions exist, because the degree of fracturing of the rock mass differs frequently and the rock mass strength is occasionally very low. Especially at the intersection of the caverns displacements increase over a long period of time. The observed system behavior is described and analyzed based on the geotechnical design taking the encountered ground conditions into account. Sequences of rock mass sections with different stiffness and strength are of high geomechanical significance due to stress concentrations in the competent areas. This had particular impact on the observed system behavior. With regard to the stability of the overall system influences of various drives and the excavation of large cross sections in several steps must be considered. Moreover, an influence of the excavation size on the extension of the area with displacement increases or stress redistributions must be taken into account.

Bolting with pumpable reactive resins – More than fixation of steel dowels in rock

“…As the excavations progressed, ongoing deformation in the cavern and cracks in the concrete shell were observed ( Figure 3) [7]. Several remedial actions were executed, such as repairing the concrete cracks and additional bolting.…”