Effect of temperature control on a tunnel in permafrost

A key problem for tunneling in permafrost is how to coordinate the excavation and lining installation in a manner that allows good excavation productivity but installs the lining quickly enough to avoid stability problems caused by thawing of the rock around the tunnel. Excavation progress and tunnel stability benefits from a lower temperature of the rock, while construction of the lining benefits from a higher temperature for the development of concrete strength. Using finite element analyses of the temperatures inside a tunnel verified by physical measurements in a tunnel in permafrost, stability conditions related to the thawing depth and suitable for use during construction have been established. These have been found to be useful as a guide for the sequencing of excavation and lining of tunnels in permafrost.