KORALM TUNNEL - RISK ASSESSMENTS AS AN AID IN THE DEVELOPMENT OF ALIGNMENT SELECTION, COST ESTIMATES AND INVESTIGATION WORKS
GERHARD HARER Project manager ÖBB – Austrian Federal Railways Austria
ABSTRACT
The most prominent tunnel along the new Koralm railway line between Graz and Klagenfurt in Austria will be the Koralm tunnel, which will underpass the Koralpe, a mountain range between the provinces of Carinthia and Styria. This double tube tunnel will have a length of approximately 32.9 km, making it to one of longest traffic tunnel projects in the Europe.
Austrian Federal Railways were authorised by the Austrian government in 1995 to undertake the planning and the design of the Koralm railway including the Koralm tunnel. Meanwhile route selection and the relevant legal procedures, especially environmental impact assessment, were concluded successfully. As a basis for the detailed and tender design for the Koralmtunnel resuming investigation works are carried out. For that purpose the construction of a system of investigation shafts and tunnels with an estimated length of 10 km, as schematically shown in figure 1, was started in 2003. Meanwhile the construction works for the Koralm tunnel have started.
Figure 1. Investigation tunnel concept for the Koralm tunnel.
The conclusion of the construction works and thus the start-up of the new railway traffic along the line between Graz and Klagenfurt is intended for the year 2018.
Geological outline
The mountain range which will be crossed by the Koralm tunnel consists of a polymetamorphic crystalline basement. Predominant lithology consists of mylonitic gneisses and micaschists, with occasional marbles, amphibolites and eclogites. The crystalline basement is bounded by master faults which have generated tertiary basins on both sides of the mountain range. The sediments of both Tertiary basins encountered by the tunnel are mainly fine-grained, clastic deposits of fluviatile and marine origin (see Fig. 2).
The recent morphological features of the Koralm massif were formed by Tertiary to Quaternary brittle faulting, weathering and erosion. Residual soils, generated by deep reaching in situ weathering and periglacial debris, cover the bedrock.
Figure 2. Geological overview of the Koralm tunnel.
Application of risk assessments
Route selection
Spatial geological information was transformed from the three-dimensional geological model to a horizontal plane at tunnel level by using the GIS, which represents a generalised model of the ground conditions as a set of map layers and their relationships.
To estimate construction time and costs for different routes a GIS-based system was developed providing a tool with which the civil engineer was able to select different routes. So decisions were not mainly based on qualitative assessments but also supported by tangible figures.
The way of defining or refining an alignment by introducing spatial information at the tunnel level appeared to be very suitable. It allowed a tunnel alignment to be defined by its major factors – tunnelling conditions expressed in cost and time with the coherently risks – and not only by civil engineering or qualitative criteria.
Risk induced assessment for cost estimates
One major task in the course of the design process is the preparation of cost estimates. The above stated GIS-supported geological and geotechnical data also provide important input data for a risk-basing cost estimation.
Considering a great number of risks and uncertainties, variation in cost could be determined in a realistic way to evaluate the risk associated with financing the project (see figure 5).
Investigation measures
A further task where risk assessment procedures in this project were used, dealt with the effects of investigation tunnels. It had to be verified that the costs of the investigation tunnels were justified by less cost due to risk reduction for the main tunnel.
The above described tools were applied most suitable for the realistic definition of geotechnical influenced input parameter as a basis for risk assessments in the course of alignment selection, cost estimates and the definition of investigation measures.