Method of excavating tunnels

Abstract

A method of excavating tunnels comprises digging an excavation to form a tunnel, gradually pushing a casing inwardly of the excavation as the excavation proceeds, the cross-sectional area of the excavation being larger than the outer cross-sectional area of the casing in order to provide a hollow annular chamber between the same; arranging at least a seal at the inner end of the casing to seal the annular section between said casing and the excavation; arranging a seal at the entrance of the excavation to seal the annular section between the casing and the entrance to the excavation; and injecting under pressure a drilling mud to completely fill the annular space between the casing and the excavation as the excavation front advances, in order to provide a fluid support for the walls of the excavation and to float the casing within the excavation, whereby friction contact between said casing and the excavation is prevented as the casing is pushed inwardly of the excavation. The excavation front is preferably worked within an end chamber to which drilling mud is also injected to avoid leakage of the drilling mud from the annular space between the casing and the excavation and to permit removal of the excavating material suspended in the drilling mud, by pumping out the same.

Dependencies are inferred from the claim text.