The under-river tunnel project of Yuan River in Changde is a twin-tube tunnel in the Chinese inland city of Changde. The tunnel connects two sides of the Yuan River, and with its two-way and four-lane, it will promote harmonious development of regions along the river. The tunnel excavation was completed in July 2019. 3360 meters of the twin-tube tunnel (each of 1680 meters long) with an outer diameter of 11.3 meters and an excavation diameter of 11.71 meters were driven by a CRCHI independently developed slurry pressure balance shield machine (SPB), which is the first set super large-diameter SPB with cutter replacement under normal pressure.
As for the tunnel’s vertical section, the maximum longitudinal gradient is 3.54%, the minimum turning radius is 680 meters, the maximum overburden is 18. 2 meters, the minimum overburden is 11.3 meters, the maximum water-earth pressure in the river is 4.5 bar, and the utmost water-earth pressure is 5.5 bar.