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Geo Informatics 1-2008
article ay tunnel figure 2. engineering geological map and section engineering geological and geotechnical survey the first stage of the work consisted of engineering geological mapping of the area and an inspection of the existing tunnel. all exposures of rock and soil were investigated in a two-week campaign by staff from itc/w+b and the ukrainian railway company uz. each exposure was characterised according to type of rock or soil, discontinuity patterns, compressive and shear strength properties, and all other features that are relevant when designing a new or enlarged tunnel. based on this survey, a detailed (1:10,000 scale) engineering geological map and cross sections were made. also the locations were selected for the latest news? visit www.geoinformatics.com subsequent site investigations for the second stage of the project. this second stage consisted of an underground campaign of four boreholes drilled to a maximum depth of 250 m and an electrical resistivity survey. the cores of the boreholes were described in detail, and pumping tests in the boreholes established groundwater levels and the permeability of the rocks. laboratory tests were carried out on selected samples from the boreholes. results the rocks in the tunnel area consist of socalled flysch deposits, which are strongly deformed and folded and include some important faults (see figure 2). flysch deposits are repeating sequences of material, starting with coarse sandstone, becoming finer sandstone and then siltstone, and ending with shale. one sequence has an approximate thickness of 1 to 20 m. this repeating sequence is expected to be a major problem in designing a new tunnel (photo 2 and figure 3). the sandstones are strong and highly permeable, while the shale is weak and impermeable. hence, a tunnel will have to go through water-bearing permeable sandstones, with a water head up to the surface to a maximum of 250 m. the weak shale will squeeze when excavated, allowing the release of stress on the sandstone and making it possible that january/february 2008 45
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