Laboratory Investigation on the Permeability Variation of Fractured Inada Granite by Multiple Transient Axial Stress Disturbances

A persistent increase in the permeability of rock mass caused by transient stress disturbances could explain the variation in groundwater level caused by earthquakes in the far-fields, increase in petroleum production due to artificial vibrations, induction of small earthquakes by seismic waves in intermediate and far-fields, etc. However, the effect of transient stress disturbances on rock permeability has not yet been fully clarified. In this study, the permeability of triaxially fractured Inada granite under multiple transient disturbances in axial stress was measured to clarify the effects of the transient stress disturbances on the fractured rock permeability. In the experiments, the permeability of fractured Inada granite decreased with time. However, the permeability increased with each series of axial stress disturbances whose amplitude was 3 MPa or larger. The degree of increase in permeability increased with the axial stress disturbance amplitudes. The increased permeability decreased with time and the duration in which the permeability decreased to its value before the disturbances was longer for larger axial stress disturbance amplitudes. The increase in permeability could be employed to enhance oil and gas productions, prevent large earthquakes, reroute underground water flow, etc.