An example of examining the effect of tunnels on each other in large diameter double tube tunnels excavated in weak soils with 3D numerical analysis, Evaluation of Bolu Tunnel support systems

Bolu Tunnel is located on the Ankara-Istanbul Highway projects which work started in 1993 and was opened to traffic in 2007. It was built as a 3-lane double tunnel. The tunnel lengths of the right tunnel are 2788 m and the left tunnel is 2954 m respectively. During the construction of the Bolu Tunnel, it was exposed to 2 earthquakes, and the Elmalık section of the tunnel, located at the entrance of Ankara, collapsed after the 12 November 1999 Düzce Earthquake. After this collapse, the tunnel route was changed. The Bolu Tunnel geologically passes through the tectonic block between the North Anatolian Fault Line mainline and the Düzce Fault. While the Istanbul side of the tunnel (Asarsuyu entrance) is located within the metacrystalline basement rocks, the Ankara side (Elmalık entrance) is located within the sedimentary rocks. These two units of the tunnel are cut by the Bakacak fault. At the entrance of Elmalık, where the biggest problems occurred during the excavation phase of the tunnel is located Elmalık fault.In this sectipn deformations of up to 1.2 m.. In addition, during the fault crossing of the Elmalık right tunnel, a collapse occurred in 1996, and in the 12 November 1999 Düzce Earthquake, the Elmalık left tunnel was completely closed. The problems experienced and the support systems developed in the Bolu Tunnels, which were designed with the New Austrian Tunneling Method, contain very valuable information in terms of tunneling. Within the scope of this study, Bolu Tunnel support systems were examined in 3D with the Flac3d program, the effect of the two tunnels on each other, the deformation changes in the top heading, bench and invert excavations were revealed.