Engineering geological investigations and the preliminary support design for the proposed Ordu Peripheral Highway Tunnel, Ordu, Turkey

Abstract This paper presents engineering geological investigations and the tunnel support design for the Boztepe tunnel of the Ordu Peripheral Highway located in northeast Turkey. In order to characterize the rock masses in Boztepe Tunnel which mainly consist of flysch (mostly alternation of sandstone, marl and siltstone) and pyroclastics (agglomerate and tuff), engineering geological investigations have been carried out in three stages as surface, subsurface and laboratory investigations. Rock mass classification systems (Geomechanics Classification System, RMR; Norwegian Geotechnical Institution Q -system and Geological Strength Index, GSI) have been utilized through information obtained from engineering geological investigations. Sixteen boreholes with a total length of 1497 m have been drilled to assist and verify rock mass classifications. Approximately seventy five rock samples have been obtained for rock mechanics tests. The information provided from all the engineering geological investigation stages has been handled in the characterization of the rock masses at the tunnel elevation. In an attempt to check the validity of empirical tunnel supports of the various rock mass classification systems, stress analysis around the tunnel opening has been executed by the 2D finite element analysis program, Phase 2 where rock mass data obtained through the rock mass classification systems have been utilized as input data. In these analyses, the empirically proposed support systems have been found to be successful to prevent further deformations around the tunnel openings.