Methane gas released from groundwater inhibits infiltration of the atmosphere
—Elucidation of a mechanism whereby bedrock near galleries remains in the reduced state even after excavation—
When excavating galleries deep underground, cracks appear inside the bedrock near the gallery. It has generally been thought that an oxidative environment is formed near galleries due to infiltration of the atmosphere through such cracks.
However, when an investigation was conducted of groundwater, gas, and rock near galleries at the underground facility of the Horonobe Underground Research Center, no signs were evident of an oxidative environment even in regions where cracks develop near the gallery, unlike in sedimentary rock areas outside Japan.
The reason for this was shown to be that gases such as methane dissolved in groundwater are released, fill the cracks around the bedrock, and flow into the gallery from inside the bedrock, thereby inhibiting infiltration of the atmosphere into the bedrock.
This research marks the first time in the world that a geological disposal research facility has elucidated an oxidation-inhibiting mechanism, taking into account the effects of released gas, with regard to the redox state near underground galleries.
By integrating and interpreting the results of investigating water quality, gas composition, and mineral composition near a gallery, it is possible to comprehensively evaluate the redox state near the gallery. The results of this research are an important finding for predicting and evaluating changes that will occur after closing a disposal site, as part of safety evaluation of geological disposal.