Engineering geological appraisal and preliminary support design for the Salarha Tunnel, Northeast Turkey

The purpose of this study is to determine the engineering geological properties of the rock masses and to recommend a convenient support design for the Salarha Tunnel located in northeast Turkey. The detailed geotechnical studies were performed in three phases as surface, subsurface and laboratory studies to assess the rock masses that mainly consist of sedimentary and volcanic rocks. Empirical, analytical and numerical methods were combined for safe tunnel design. The RMR, Q and NATM systems were used as empirical methods to define the rock masses and to determine the preliminary support design. The convergence-confinement analytical method was utilized. The performance of the suggested empirical support design, extent of the plastic zones and deformations were analyzed by means of the finite element method (FEM)-based 2D and 3D numerical modeling. According to analytical and numerical analyses results, the empirical support design was sufficient to prevent stability problems developing around the rock masses surrounding the tunnel. The interpretations of results demonstrate that the 3D numerical method seems to fit even better with the respective outcomes from the analytical method. Thus, it is suggested that the empirical, analytical and numerical methods should be combined for a more reliable support design.