Geological and geotechnical evaluation of Baskale Tunnel (entrance and exit portal section)

The Baskale Tunnel (Van-Guzeldere) is built narrow strait where great difficulties are experienced and hard topography conditions. In this study, geological units in the Baskale Tunnel route have been examined in terms of engineering geology. Baskale Tunnel is situated in the Kırkgecit formation consisting of conglomerate-sandstone-mudstone-limestone intercalations. In order to determine the engineering properties of the geological units along the tunnel line, laboratory tests were carried out to identify the engineering properties of the units such as uniaxial compressive strength, point load strength index, elasticity modulus, poisson ratio, density on the core samples obtained from the borings made at the entrance and exit parts of the tunnel. Field studies and laboratory analyzes indicated that conglomerate-sandstone-mudstone-limestone units are weak rock characteristics. In order to evaluate the rock mass characteristics of the units and the support system for the tunnel, RMR, Q, GSI and NATM rock classifications were determined by utilizing from borehole, field study and laboratory test results. Numerical modeling was performed under different seismic loads using the finite element program "Phase² 8.0 and the validity of the support systems for the tunnel is discussed for both the entrance and exit portal sections . In addition, the results obtained from the numerical analyzes were compared with the displacement measured from tunnel.