With the Koralm Railway Line, the cities Graz and Klagenfurt are to be connected by a new,
124 km long, high-perfor-
Along this 24 km long section, numerous bridges,
a subsurface route (total length 5.2 km) and a lengthy underpass below the
A9 Pyhrn Motorway (built with open cut method) are planned. Furthermore, the Hengsberg Tunnel with a total length of 1.7 km
is situated along this project. 1.0 km of the tunnel is being built using the mining technique. For the remaining section
cut-and-cover methods are used. On the one hand, a bottom-up method with bored pile walls as side support, and on the other
hand a top-down method (also between protecting bored piles) have been implemented.
BGG Consult has been attending to this project section in the field of geotechnics, hydrogeology and geology since the
feasibility evaluation phase. Initially, expert's reports have been compiled in the route selection process. For the
environmental impact assessment, the fundamental facts were integrated in the expert's report on ground water / mountain
water (including geology). Subsequently, the application documents for the construc-
tion permission and the expert's reports
for the tenders were prepared. All conclusions have been based on the results of extended subsoil explorations.
During construction, geo-
technical and hydrogeological consulting is provided by BGG Consult. This includes the optimisation
of foundations, building pits and dewatering concepts as well as the supervision and monitoring of the extensive earth works.
At the southern side of the Hengsberg Tunnel, cover layer material and highly weathered "Miocene" respectively exist across
the tunnel section over a length of 600 m. In addition to that, slope deformations have been detected above the tunnel
alignment. Due to this adverse subsoil situation and in order to avoid extended temporary cuts, a cut-and-cover tunnel between
two bored pile walls has been selected - in coordination with the tunnel designer - as the appropriate construction method,
already in the early stages of the project. Over a length of 400 m, an arch section (see picture) is being carried out. In the
remaining 200 m of the open cut, a rectangular section with excavation under the tunnel roof has been designed. The ground water
exchange is accomplished by filter layers placed below the structure.
The example of this project illustrates that it is possible to handle also difficult subsoil conditions without cost increase
and time delay, if the subsoil situation is assessed - based on an accurate exploration - adequately and early enough.