Development of stress conditions around a tunnel excavated in argillaceous rock related to change of saturation conditions

Uehara, Shinichi*; Kobayashi, Akira*; Chijimatsu, Masakazu*; Onishi, Yuzo*; Fujita, Tomoo 

This paper reports the results of calculations about coupled hydro-mechanical process in the domain around excavations at clay rock site at Tournemire, France. We operated the numerical modelling by using a Finite Element Method code named THAMES, on the assumption that swelling pressure is parallel to saturation ratio. The results of modelling indicated that saturation ratio changes seasonally at the domain within several tens cm from tunnel wall. This extension is similar to that of damage zone observed in the tunnel at Tournemire site in 1881, which supports the idea that the saturation-desaturation cycles has decreased the rock strength and caused damage zone extension. The modelling results also suggested that the consideration of swelling pressure could affect evolution of stress state abruptly.