[SSS17-P14] Dynamic water permeability change of simulated fault induced by moderate velocity friction
Keywords:permeability, friction coefficient, fault
In this study, Belfast dolerite and Aji granite were used as test specimens. For each experiment, two 20-mm-long hollow cylindrical specimens with 40 mm and 16.5 mm outer and inner diameters, respectively, were used. To measure the permeability, radial flow from the inner wall to the outer wall of the specimen was induced by applying a differential pre pressure between inner and outer walls. 0.1 to 0.8 MPa of constant pore pressure was applied from the inner wall, and water flowing out from the outer wall was released to the atmosphere. I applied constant normal stress of 2 MPa and constant rotation speed from 0.1 to 100 rpm (0.001 to 0.1 m/s) for a slip displacement of 1 to 10 m.
The result shows that permeability (flow rate) increased suddenly at the onset of sliding by a factor of more than two, and the rate of increase was nearly proportional to permeability before sliding. After sliding, permeability was decreased gradually with time, and had almost stabilized within few minutes. To compare the permeability before and after sliding, higher velocity friction (>0.03 m/s) results in the increase of permeability, and slower velocity friction induced the permeability reduction. This transition appears to be related to velocity dependent friction behavior, as velocity weakening was observed at above 0.03 m/s of slip velocity. Permeability reduction and velocity weakening behavior at slower velocity regime is probably explained by gouge compaction and gouge friction. On the other hand, high velocity friction will produce thermal pressurization, flash heating, and thermal cracking, therefore, the transition process of water permeability for high velocity friction would be more complicated than slow velocity friction.