This paper presents an application of the rock mass classification systems, namely, Geomechanics Classification System (RMR), Geological Strength Index (GSI) and the newly adapted A-RMR for the characterization of the rock masses surrounding the portals of the Ordu Peripheral Highway Tunnel. In order to characterize the rock masses, 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 along the tunnel route. Sixteen boreholes with a total length of 1497 m have been drilled along the tunnel route to assist and verify rock mass classifications. Approximately, seventy five rock core samples have been obtained for rock mechanics tests. The shear strength and geomechanical properties of the rock masses were assigned as a result of a synthesis of the results of laboratory testing, GSI, RMR and the newly adapted A-RMR methods. The information provided from all investigations has been gathered and handled for the characterization of the rock masses governing the portal slope stability of open-cut excavations of the tunnel. Kinematical and limit equilibrium analyses of the tunnel portals have been employed for portal slope stability considerations.


Being settled like an entrance gate of the Black Sea Region of Turkey, Ordu is a city of great beauty of the nature. Ordu owns the longest shoreline with the top quality beach sand of the surrounding region. The proposed Ordu Peripheral Highway has been planned to deviate at KM: 21+000 from the Bolaman – Ordu Highway and join the existing Ordu – Giresun highway at KM: 40+114 (Figure 1). This proposed inland road encompasses various structures such as, double tubed tunnel sections, open-cuts, bridges, viaducts and junctions. The only major geotechnical concern in this paper, however, is the tunnel portal stability analyses through empirical rock mass classification systems. In this framework, among the two existing double tubed tunnels, the Boztepe (T-1) tunnel will be studied in detail.


The project area regarding its geological characteristics can be included in the central part of the Black Sea Region. While the eastern portion of the Black Sea Belt is mostly represented by volcanic rocks, the western part is dominated by sedimentary rocks. In this frame, the project area accommodates volcanic rocks together with contemporaneous sedimentary rocks (Terlemez and Yõlmaz, 1980).

(Figure in full paper)

Upper Cretaceous aged Mesudiye formation is the oldest lithostratigraphic unit near the project area and its lower bound can not be observed. The inferred thickness of this formation is about 1000 m. Both tunnel alignments will be mostly cut by the Mesudiye formation which is comprised of agglomerate, basic lava flow, limestone, tuffite, mudstone, siltstone and sandstone. The description of this formation was first made by Terlemez and Yõlmaz (1980).

Another formation to be driven by the initial portion of the Boztepe tunnel is Akveren formation which may be correlated to the Fatsa formation of Terlemez and Yõlmaz (1980).

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