Formation mechanism of extension fractures induced by excavation of a gallery in soft sedimentary rock, Horonobe area, Northern Japan

This paper focuses on the formation mechanism of fractures induced by excavation of a gallery in soft sedimentary rocks in the Horonobe area of Japan. Detailed fracture mapping of the gallery indicates that the fractures consist of both pre-existing shear fractures and excavation damaged zone (EDZ) fractures. EDZ fractures correspond to weak planes associated with bedding planes or transgranular cracks. The EDZ fractures terminate against pre-existing shear fractures. Therefore, even for excavations in soft sedimentary rocks, formation of the EDZ fractures are controlled by pre-existing fractures and earlier weak planes.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Fractures can be divided into pre-existing shear fractures and EDZ fractures. ► EDZ fractures correspond to weak planes such as bedding planes or transgranular cracks. ► Even for excavations in soft rocks, formation of the EDZ fractures is controlled by weak planes.