A shield tunneling method for enlarging the diameter of existing tunnels: Experimental investigations

As for the construction of a metro line, excavated stations usually serve as departure and receiving shafts of the shield tunneling machines, used for drilling of station-to-station tunnels. However, the shield tunneling machines may reach the stations before their excavation. In order to avoid stopping of tunneling to wait for the completion of the station, a Shield Twice Tunneling Method (STTM) is developed and applied to a real engineering example. It permits the station-to-station tunneling machines to pass through the stations first. Subsequently, larger -diameter shield tunneling machines are driven from one end of the station to the other one. The resulting tunnels serve as side-platform stations. A model test, simulating the tunneling process of the larger-diameter shield tunneling machines, was carried out. It was designed according to the concept of equivalent specific energy. The experimental results corroborate the rationality of the selected tunneling machine and of its equipment with cutters. In addition, suitable tunneling parameters are provided. The average values of the thrust forces and the torsional moments are predicted, based on the results of the model test. They agree with the monitored results on site. This demonstrates the usefulness of the model test. Application of the STTM to a real engineering project shows that the entire construction period was reduced by 45%.