An Empirical approach to disposal tunnel design and sealing in Neogene sedimentary rocks

早野 明  ; 青柳 和平  ; 村上 裕晃  ; 木村 駿  

Hayano, Akira; Aoyagi, Kazuhei; Murakami, Hiroaki; Kimura, Shun

An empirical approach is being implemented at the Horonobe Underground Research Laboratory in Neogene sedimentary rocks to integrate technologies for optimizing the layout of disposal tunnels and pits. Key evaluation items include tunnel and pit mechanical stability and spacing, both influenced by the excavation damaged zone. Water inflow is also evaluated to ensure the constructability of excavation and buffer placement. Prediction methods for geological and hydrogeological conditions have been developed, and in situ investigations are underway in the 500 m Niches Nos. 8 and 9. Sealing measures such as tunnel backfilling and hydraulic plug installation are essential for closure and should be transferable to other rock types. Accordingly, an in situ construction test is being prepared in the 350 m Niche No. 6, supported by site investigations and laboratory and feasibility tests of construction methods and materials. A full scale construction experiment is scheduled for the second half of 2026.