2nd International Conference on Tunnel Boring Machines in Difficult Grounds (TBM DIGs Istanbul), İstanbul, Turkey, 16 November 2016, pp.288-291
Uskudar–Umraniye–Cekmekoy Metro Project (UUCMP) is the second metro line of Istanbul in the Anatolian side which has 17 km twin-tube-main-route tunnels, 16 metro stations, and a 2.8 km long connection tunnel between the depot area and the main metro line. The New Austrian, Tunneling Method (NATM) and the earth pressure balanced tunnel boring machines (EPB-TBM) are used to build these metro tunnels. The main metro line tunnels are planned to be built by TBMs. Metro station platform tunnels, switch tunnels and the depot area connection tunnel are planned to be built by NATM because of the different cross section of these tunnels. At the beginning of the metro Project, the depot connection tunnel which has 74 m2 cross section is planned to be done by NATM. However, extra soil borings showed that soil conditions requires the umbrella arch method (UAM) for at least half of the depot connection tunnel line. Therefore, it is investigated that if this single tunnel can be built as two (twin) tunnels by TBMs which will have 2 * 34 m2 cross section. It is calculated that building the depot connection tunnel by TBMs as twin tunnels is more economical and faster than building a single big tunnel. At the end of the construction of the depot connection tunnels with TBMs, it is observed that by changing the depot connection tunnels from NATM to TBM, the construction cost decreased from 29.186.670 € to 20.608.000 € and the construction duration decreased from 844 days to 495 days for tunneling except the duration for the supply of TBMs. As a result, it can be said that in Uskudar–Umraniye–Cekmekoy Metro Project (UUCMP) by changing the tunneling methodology from NATM to TBM depending on the soil conditions, the depot connection tunnels are completed with 29 % less cost and approximately one year earlier.