In the context of constructing the eastern tube of the Karavanke road tunnel, extensive geological, geotechnical, and hydrogeological investigations have been conducted since December 2015. The investigations were carried out both from the surface—at the portal area and above the planned tunnel alignment—as well as from exploratory niches within the existing tunnel tube. It has been known since the original tunnel construction that the geological conditions in this area are highly challenging.
The geophysical investigations were aimed at assessing:
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lithological and mechanical conditions in the future portal zone,
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lithological, structural, and mechanical conditions in the zone of shallow overburden (particularly the properties of near-surface unconsolidated sediments),
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seismic characteristics of the carbonate and Permo-Carboniferous formations, including dynamic elastic moduli and Poisson’s ratios relevant to the alignment of the eastern tube.
One of the main challenges was the execution of borehole seismic tests in sub-horizontal boreholes drilled from the exploratory niches. To perform these measurements, we developed a custom-designed measuring probe, which represents an innovation in the field of borehole seismic investigation.
The measurement data obtained were of high quality, and the results of the geophysical surveys provide reliable, in-situ quantitative input for geological–geomechanical analyses and for the design of the tunnel structure.