Evaluation of shaft excavation technology based on construction results up to a depth of 500m at Mizunami Underground Research Laboratory

Sato, Toshinori  ; Mikake, Shinichiro ; Noda, Masaru*; Kobayashi, Shinji*

The Japan Atomic Energy Agency conducts studies and research associated with the excavation of underground research facility at the Mizunami Underground Research Laboratory in Mizunami City, Gifu Prefecture. The research laboratory is an underground facility consisting of two shafts and some drifts and excavation has currently extended to a depth of 500 m. This report contains the evaluation results of measures to control the welling of water and measures to prevent ground collapse based on construction records up to now. For measures to control the welling of water, we carried out pre-grouting from umbrella-shaped grouthing holes placed at the bottom of the shaft and observed improvements in given permeability. For measures to prevent ground collapse, we conducted safe shaft sinking along faults by combining reinforecement works using rock bolts and fore-poling works using silica-resin grouting. Both measures were conducted using a shaft sinking drill carriage "Shaft Jumbo" that made it possible to efficiently incorporate short step shaft sinking cycles.