Abstract
The Ovit Mountain Tunnel (OMT) is an highway tunnel under construction at Mount Ovit between Ikizdere (Rize) and Ispir (Erzurum) in NE Turkey. It will be the country's longest tunnel about 14700 m long in twin tubes. This paper compares and assesses tunnel excavation by Tunnel Boring Machine (TBM) excavation or drill and blast method for the OMT. Rock mass and material characteristics were evaluated to identify the excavation method. The rock mass classification of the tunnel grounds was performed by utilizing the Rock Mass Rating (RMR), Q system and New Austrian Tunnelling Method (NATM) which was followed by a geotechnical investigation along the tunnel. Twelve boreholes with a total length of 1116.5 m were drilled to assist and verify rock mass classifications. Seventy five rock samples were obtained for mechanical test. TBM method was selected at preliminary design stage of the OMT. But now, the OMT is driven by drill and blast method, using hydraulic excavators and the support is based on the principles of the NATM. The selection of this tunnelling excavation method was decided by morphological site conditions, geological, geotechnical site conditions, time and economic criteria.
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