Nefise Akçelik Tunnel

The Nefise Akçelik Tunnel is located within the boundaries of Ordu Province as part of the Black Sea Coastal Road Project, between the districts of Perşembe and Bolaman. The tunnel consists of two tubes, each with dual lanes, and at a total length of 3776 metres, it is one of Türkiye’s longest dual-tube road tunnels. Both tubes were constructed to ensure uninterrupted and safe traffic flow. The design depth at the tunnel portals is 33 metres, while along the alignment it varies between 75 and 375 metres.

^{Nefise Akçelik Tunnel (}oyakcimento⁾

The tunnel is named after Nefise Akçelik, one of Türkiye’s first female civil engineers, who pioneered tunneling projects under the General Directorate of Highways. The naming honors her contributions and legacy. Akçelik actively participated in the planning, design, and execution of tunnel projects and served as an inspiration to the industry through her leadership in engineering.

The area where the tunnel was constructed features a geomorphology shaped by high tectonic activity, deep valleys, and steep topography. Engineering risks include fault and fracture systems formed by recent tectonics, extensive weathering zones, and groundwater seepage. The tunnel was excavated through medium to weak volcanic rocks (basalt, tuff, and agglomerate). Particularly high deformation risks were identified in the sections between Km 10+683 and Km 10+800 on the left tube and between Km 10+693 and Km 10+742 on the right tube.

^{Aerial view of the Nefise Akçelik Tunnel (}UAV⁾

Tunnel excavation was carried out in accordance with the New Austrian Tunnelling Method (NATM). Problematic zones were classified as A2, B1, B2, and B3, and support systems were designed accordingly. The following support systems were employed:

• Shotcrete (typically reinforced with Q180/180 mesh)
• Short rock bolts (4 to 6 metres in length)
• Steel sets (used sparingly; I120 profile for B3 zones)
• Inner lining: unreinforced, 40 cm thick, cold-jointed reinforced concrete structure

As a result of insufficient support elements, lateral deformations of up to 14 cm were measured on the tunnel walls.

USTA (Expert System for Tunnel Analysis), developed by Istanbul Technical University (ITU), is a software capable of analyzing data collected during tunnel construction in digital format, monitoring displacement trends, velocities, and accelerations. Developed using Visual Basic 6.0, USTA operates with Microsoft Access databases and generates reports in Excel and Word formats.

Applied to the Nefise Akçelik Tunnel, USTA provided the following warnings based on displacement data recorded at point Km 10+714.50:

• "Stresses are concentrated on the left shoulder; spalling may occur."
• "Due to discontinuities, advance forepoling should be used and excavation steps should be shortened."
• "Deformations are expected due to fault zones; a reinforcement plan should be developed."
• "Groundwater may have an effect; the drainage system should be improved."

The program also calculated in-situ geomechanical parameters for use in tunnel support design, including an internal friction angle of φ = 30° and a cohesion value of c = 2.23 MPa. These values showed strong agreement with results obtained through the finite element method.

The Nefise Akçelik Tunnel holds a unique place in Türkiye’s tunneling history, not only because it was successfully completed under challenging ground conditions using applicable engineering solutions, but also because it was among the first projects supported by domestically developed expert system software. It also stands as an important symbol highlighting the contributions of female engineers to the sector.