Tunneling in Swelling Rock - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 755

If the disturbed rock zone crosses the tight zone, which is formed at the anhydrite sur-
face, water can permeate in the area of the tunnel. In addition, water may flow in lon-
gitudinal direction through the disturbed rock zone. The latter effect can be prevented
by sealing structures that are located near the transition zones from the leached wa-
ter-bearing rock to the unleached Gypsum Keuper (Fig. 23.1). If the tunnel section
in between the sealing structures has a sufficient distance to the anhydrite surface and
remains dry, it can be designed for a relatively small swelling pressure. At the “wet” side
of the sealing structures located in unleached Gypsum Keuper swelling pressure can
occur and an increased thickness of the internal lining may become necessary (Fig.
23.1, Wittke 2012a).
Figure 23.2 Anhydrite surface above the tunnel roof, FE-mesh and boundary conditions
Figure 23.4 shows a possible concept of such a sealing structure, which consists of two
sealing rings for reasons of redundancy. In a first step of construction, the disturbed
rock zone must be smoothly removed and then filled with reinforced concrete. The con-
crete serves as abutment for grouting of synthetic resin which allows the sealing of
very small fissures. After grouting the sealing rings are completed. Finally, the internal
lining is installed and connected to the sealing rings by means of waterstops. Between
both sealing rings a circumferential drainage for the purpose of inspection should be
arranged to show whether or not further grouting is required.