In situ stress measurement using hydraulic fracturing for shallow tunnel in Korea

In situ stress measurements using the hydraulic fracturing technique have been conducted in Korea during the preliminary design site investigation for the Taejon subway tunnel. In situ stresses were measured in 3 shallow boreholes along the axis of a planned tunnel. The magnitude of the maximum horizontal principal stress was in the range of 2.1 similar to 2.7MPa between 25 and 50 meters deep below the surface. Its orientation was in the range of 80 degrees similar to 100 degrees clockwise from the true north, and the direction of the proposed tunnel axis was nearly 65 degrees. Rock mass conditions along the proposed tunnel alignment were characterized with closely spaced jointing and slightly to moderately weathered granitic rock. Numerical analysis using the finite difference code was performed considering the measured in situ stress field.