The pipe-jacking method which use the tunnelling machine have often been adopted in the construction for the pipe of gas and sewage. The performance of a tunneling machine in rock mass is usually evaluated based on the intact rock strength and the rock mass property including the crack. However, the performance is affected by not only its compressive strength but also the comprehensive characteristics including the type and properties of rock-forming minerals. In this study, mechanical properties of rock-forming minerals contained in some granite were evaluated by depth sensing indentation test (DSI test). The relationship between these properties and difficultly of excavation was also discussed. As a result, the intact rock strength of the granite in which the excavation trouble occurred was smaller than that of other granites, and the mechanical properties of feldspar grains contained in the granite were remarkably different from those of other granites. These test results suggest that the mechanical characteristic of minerals greatly influence the performance of excavation with a tunnelling machine, and DSI test is useful to clarify these properties.
