The article presents experiences gained during construction of the approximately 3 km long urban Lainzer Tunnel (LT31), driven with side-wall galleries under shallow overburden. The structure's safety is assessed mainly on the basis of 3D deformation analyses, comparison of predicted and observed system behaviour, evaluation of shotcrete stress, and online monitoring of surface settlements. Displacements of the tunnel face, correlating with pre-face surface settlements, are monitored by an innovative, fully automatic face monitoring system (OBM). A correlation between volume loss (surface) and volume increase (face) could be established. A test field comparing fibreglass anchors (GRP) with IBO face bolts revealed -contrary to expectations -no appreciable reduction of surface settlement due to GRP anchors. However, temporary inverts constructed in the side wall galleries in combination with IBO face bolts support turned out to be effective in reducing horizontal convergence and resulting settlements of the ground surface in a sensitive residential area.
This report gives an overview of the ventilation scheme for both tubes of the Tauern Tunnel with particular attention to the rebuilding of the multi-storey ventilation cavern. The cavern was designed and constructed in the 1970s -along with most of the ventilation system -and provides the ventilation for the central sections of both tubes with a ventilation shaft about 600 mm deep. While the original scheme intended sheet metal ducts partly suspended from the cavern vault, all the extract air ducts now had to be constructed of reinforced concrete as part of the construction of the second tube on account of the requirement for fire resistance. This also included the replacement of existing suspended sheet metal ducts.The design work was a particular challenge because the structural design and detailing also had to consider the complicated existing structure and the aerodynamic (flow resistance) and logistical (maintenance of traffic and continuous operation of ventilation) aspects.
With the introduction of Eurocodes, non‐linear methods are now explicitly permitted for the determination of internal forces. Although the application of Eurocode 7 has not been intended for tunnel construction, it is applied in practice. Tunnel linings are treated as retaining structures in the sense of Eurocode 7. The choice of the Design Approach to be applied is specified in the National Annex (NA) of each country. The application of a standard to a field which was not intended for the purpose naturally leaves room for diverse interpretation. A working group was established by the Austrian Society for Geomechanics (ÖGG) to develop a consistent design strategy for tunnelling. Recommendations based on comparative calculations have been developed for the design of sprayed concrete linings. This article summarises the findings of the investigations carried out.
The article describes the fundamental geotechnical model assumptions in the design phase of the Semmering Base Tunnel. Two selected case studies show the verification of the geotechnical model during tunnel construction. The verification process is essentially based on geotechnical monitoring in combination with specific back analyses. It is shown that particularly in complex geotechnical conditions, such as deep tunnels in weak rock mass, the designer can only assess a range of expected behaviour. Most information about system behaviour and thus about the geotechnical model conceptions can only be gained during construction. An improved understanding of the geotechnical model provides the potential to identify and minimize geotechnical risks earlier and to adapt excavation and support measures to the actual conditions.
The Semmering Base Tunnel with a total length of approx. 27 km is being driven through a complex system of fault zones. During the investigation period, technically demanding site investigations were carried out to obtain information on geological and hydrological conditions including the determination of the strength and stiffness of the faulted zones. The results formed the basis for the geotechnical design, performed according to the Guideline for the Geotechnical Design of Underground Structures with Conventional Excavation published by the Austrian Society for Geomechanics. According to the regulations, the system behaviour must already be tested against the designed support measures during the design stage. In this case the behaviour was assessed using a complex 3D Finite Element model. The expected and therefore predicted system behaviour represents the baseline for the observational method.
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