Geomechanical model for sedimentary soft rock based on surface-based investigations

Sugita, Yutaka ; Sanada, Hiroyuki; Matsui, Hiroya 

Japan Atomic Energy Agency (JAEA) has been conducting the underground research laboratory (URL) projects in Neogene diatomaceous rock at Horonobe-cho, Hokkaido, Japan. This paper summarizes development in surface-based investigations of a geomechanical conceptual model and estimation of physical and mechanical parameters for prediction of mechanical behavior of the rock mass in response to excavation of the facility. From the results of the surface investigations on rock mechanics, it is clarified that rock mass is divided into three zones, and that rock mass memorizes the mechanical properties depend on the original geological conditions at the sedimentary period, though present geological structure is complex due to folding and faulting. Hence the three-dimensional distribution of rock properties can be estimated and developed taking the geological structures (stratigraphy, displacement due to folding and faulting) into account.