Relationship between rock mass properties and damage of a concrete lining during shaft sinking in the Horonobe Underground Research Laboratory Project

Tsusaka, Kimikazu; Inagaki, Daisuke; Nago, Makito*; Kamemura, Katsumi*; Matsubara, Makoto*; Shigehiro, Michiko*

Japan Atomic Energy Agency (JAEA) has been constructing three shafts to a depth of 500 m in the Horonobe Underground Research Laboratory Project. In this study, in consideration of support patterns installed, a relationship between the rock mass properties and mechanical response to excavation was investigated in detail during the construction of the East Access Shaft below a depth of 250 m. Since the shaft has intersected several faults with the size greater than the shaft diameter, some amounts of rock spalling have occurred and cracks have severely developed in a concrete lining in highly fractured zones. The results of pre-excavation grouting were compared with the results of fracture mapping in the shaft wall obtained during the shaft sinking. Applicability of several support patterns installed to control massive spalling during the shaft sinking was also analysed using the results of geometry profiling of shaft wall using a three-dimensional laser scanner and convergence measurements. As a result, based the empirical relationships among the characteristics of rocks, dimension of spalling, damage of a concrete lining and support patterns, a flow chart for selection of span of a concrete lining was proposed to control its severe damage prior to shaft excavation.