A TBM Application in Shallow and Weak Ground Conditions (Ankara-Izmir High-Speed Railway Construction Project, Türkiye) Available to Purchase

Tunneling in weak ground and shallow conditions is an extremely difficult task for tunnel engineers. However, depending on the increase in demand for high-speed railways, it requires the construction of many tunnels. The weak rock mass forms the route of the T1 tunnel constructed within the scope of the Ankara-İzmir High-Speed Railway Project. The main purposes of the study are to compare the performances of NATM and TBM in a large diameter railway tunnel, and to present a successful TBM application. The length of the T1 Tunnel is 3047 m and, the tunnel is the longest tunnel of the Ankara-İzmir High-Speed Railway Construction Project. The inner diameter of the tunnel is 12.5 m. The tunnel allows high-speed train passage through a single tube, as well as an escape tunnel. With this feature, it is Türkiye's first single-tube tunnel containing both a railway and an escape tunnel. In addition, the T1 tunnel is the railway tunnel with the largest diameter in Türkiye, constructed with TBM. In the first stage, the T1 tunnel was designed in accordance with NATM principles. The estimated advance rate with NATM was estimated 2.4 m/day while that of with TBM is 10 m/days. Considering time limitation, use of TBM was decided for constructing the tunnel. The overburden along the tunnel varies between 3.7 m – 80.0 m. The lithological units along the tunnel route are gneiss, mudstone, and sandy mudstone. The rock masses along the route are highly weathered and weak character. Consequently, the T1 tunnel was constructed with TBM, successfully. Although the average advance rate was measured as approximately 16 m/day, hence the TBM outperformed. The main reasons for the high performance of the TBM are well-known geological and geotechnical conditions of the tunnel route, and the selection of a suitable TBM.