Numerical Modeling of NATM Tunnels Pre-Supported with Umbrella Arch Method: Comparison with Field Measurements

Pre-support systems are required in New Austrian Tunneling Method (NATM) construction in weak soils, shallow overburden conditions, in areas of settlement-sensitive structures. Umbrella arch method (UAM) is one of these pre-support systems that generate an artificial improved roof, before the excavation. In this study, a section of the Çekmeköy-Sancaktepe-Sultanbeyli Metro Line (with twin tunnels) constructed with NATM and UAM support system is modeled and analyzed using finite element method. The tunnel section was modeled using three approaches (i.e., plate, dummy plate, and individual pipe), and the results were compared with the field measurements. The results of the numerical analysis agreed with the field measurements. The dummy plate approach resulted in more accurate settlement predictions compared to other approaches. The results also indicate that the tunnels were far enough, such that the surface settlement profile did not indicate a clear impact due to the sequence of construction of the twin tunnels.