The Semmering Base Tunnel (SBT), with a total length of 27.3 km, is one of the leading construction projects of the Baltic-Adriatic Railway Network. The tunnel connects the two federal provinces of Lower Austria and Styria and cuts through the eastern part of the Alps. The construction lot SBT 1.1-Tunnel Gloggnitz is characterized by a complex geological- and hydro-geological architecture containing alternating competent geological structures, major fault zones, and corresponding geological transition zones. There are three main water-bearing formations at the construction lot SBT 1.1: (a) Karst-prone blocky limestone with an initial water pressure of 10 bar. The discontinuities form a highly permeable interconnected joint network with a significant storage coefficient of the groundwater table. (b) Massive to blocky dolomite with an initial water pressure of 25 bar. The systematic discontinuities and disturbed zones of subsidiary structures with karst form a permeable, interconnected joint network. (c) The transition zone of the limestone to base structure marks the most challenging area for consolidation- and sealing grouting. Weak fault rocks characterize transition zones with intense fracturing. However, as subjected to high groundwater pressure of 10 bar, these zones are associated with the potential of flowing ground conditions. Based on the overall project requirements, specific drilling- and grouting methods and materials for pre-excavation grouting have been established and successfully implemented in the construction process. The innovations include a Standpipe-Packer substituting a conventional steel standpipe, a specifically cased drilling system with grouting inserts to prevent erosion within the borehole and allow for defined grouting. In addition, this Grouting-Pipe system replaces standard tube-à-manchettes and controls the flushing while drilling with preventers. Finally, a combined cement-polyurethane grout mix (Hybrid Grout) was implemented to stabilize the grout. The implementation of these measures will be discussed in detail, and their benefits to the construction process will be highlighted.
Grouting into an open borehole is a process that has been well described academically. Numerous grouting techniques and grouting criteria are available for various applications and combinations of rock mass/ground. Tube á manchette (TAM) or sleeve port grouting systems have until now mostly been used in specialized civil engineering work in soft ground. In order to be able to carry out grouting successfully in faulted rocks, cased drilling is necessary in order to maintain the stability of the borehole for the insertion of the sleeve pipe. Under these premises, fundamental considerations for successful TAM grouting in faulted rocks are presented. The rheological properties of the grout used, the form and size of the injection opening and the strength and thickness of the sheathing compound significantly influence the penetration into the surrounding rock mass. Increased effective pressure is necessary in order to break through the sheathing compound and also to overcome friction losses during the grouting process. The necessity of high effective pressure and the emergence of the grout at the sleeve ports can, in contrast to an open borehole, increase the risk of jacking the ground in the course of grouting and this has to be carefully taken into account and investigated in advance. The interaction of effective grouting pressures and friction losses of the grouting system and their effect on the grouting process in faulted rock are described through the formulation of a general grouting criteria for TAM grouting.
Base tunnels usually require temporary intermediate construction accesses in order to be able to carry out the tunnelling work in a timely, economical and logistical reasonable scope. Intermediate construction accesses in the form of shafts lead to particular logistical challenges in supplying the tunnel headings. At contract SBT 1.1‐Tunnel Gloggnitz as the eastern section of the Semmering Base Tunnel, the shafts of the intermediate construction access Göstritz cannot be sunk from the surface for topographical reasons but are instead developed by an access tunnel. This fact requires the construction of complex underground structures and logistical interfaces to supply the four tunnel headings, beginning from the building site facilities, via the access tunnel, through the shafts to the tunnel face. In addition to the ongoing supply of all kinds of support measures, the excavated material is mucked by means of fully automatic belt and shaft conveyor systems. To ensure the permanent safety of the crew on‐site, the highest demands and resilience are placed on the transport systems through the two 250 m deep shafts, the ventilation and the mountain water drainage systems of up to 500 l/s. The article describes the experience and ongoing optimization of the logistics concept as well as innovative new developments that are applied in this special tunnel project.
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