ABSTRACT
In recent years, the rapid growth in urban development has resulted in an increased demand for the construction of tunnels for electric and communication cables, and transportation systems. For obvious practical reasons such as accessibility, serviceability and economy, these tunnels are constructed by shield machines of large diameter and at shallow depths. The Groene Hart Tunnel, constructed in 2005 in Netherlands, was carried out by a slurry-shield machine with an outside diameter of 14.87 m. The M-30 Tunnel in Madrid excavated by EPB shield machine, 15.2 m in diameter, was until recently the biggest shield tunnel completed in the world. In September 2006, two massive 15.43 m diameter slurry shield machines began work on Shanghai Yangtze River Tunnel. With the increase of the shield tunnel diameter, the excavated volume is increased dramatically and the probability of excavation in complicated stratum with different types of soil layers increases greatly too. The stability of the soil itself decreases at the same time. Thus, in recent years, more and more attention was paid to the face stability of large shield-driven tunnels.
