Mechanical behavior of closely spaced tunnels – laboratory model tests and FEM analyses

Pingnian Tunnel is a typical twin-tunnel, which was constructed in accordance with the principles of the New Austrian Tunneling Method in weak rock, being part of Luofu expressway in Yunnan Province. Tunnel width is 12.5 m, and the length is about 360 m. Spacing between two tunnels changes from 18 m (at Luochunkou site) to 25 m (at Funing site).The tunnels are under the inclined ground surface and the two tunnels are not constructed in the same level, and the vertical distance between them is from 3 m to 4 m. The typical cross section is shown in figure 1.