Abstract

Conventional Korean tunnel portals require a lot of overburden. For stability reasons, about 1.5 to 2.0 times the tunnel diameter is needed for the height in order to achieve a sufficient arching effect. Thus, considerable movement of earth and support constructions are required which lead to undesirably large changes of and damage to the environment. With a massively designed pipe roof, tunnels at low overburden can be built. To effectively construct pipe roof as an advanced safeguarding method, the following properties are indispensable: stability, insensitivity to settling and drilling accuracy. A new pipe roof method, AT-casing system, has been developed which on the one hand entirely combines the properties mentioned above, and which on the other hand permits the construction of safe, economical and environmentally friendly tunnels at low overburden heights of 3 to 5m.