An Experimental System to Evaluate Dynamic Double-Direct Slip Process of Stressed Fault

Earthquake is one of the most devastating natural hazards, causing severe consequences worldwide. The direct shear tests provided practical approaches to reveal the shear instability and failure of faults. The undesired friction between the normal loading platen and the specimen edge in the direct shear testing system has a nonnegligible influence on accurately observing the shear rupture process and the slip mechanism of faults or rock discontinuities. Consequently, the instability and failure process of geomaterial discontinuities has been widely evaluated using the double-direct shear tests under static loading. Meanwhile, the dynamic shear rupture and slip process on the fault under in-situ stresses is crucially responsible for investigating the rupture speeds, rupture propagation, and rupture mechanism of the discontinuities. However, the existing double-direct shear methodology and system are not valid for conducting dynamic double-direct shear experiments under high loading rate conditions. Thus, to evaluate the dynamic slip process of discontinuities, a novel dynamic double-direct shear experimental methodology was proposed in this study. The Hopkinson bar is used to exert dynamic shear force on the discontinuities, and the biaxial static loading system is designed to apply normal stress on the discontinuities. The 2D displacement field of the double-fault structure under dynamic loading conditions is quantified to reveal the dynamic slip process of faults. The results indicate that both the dynamic loading rate and the normal stress have considerable effects on the peak shear stress of faults. The displacement of the upper discontinuity is almost identical to that of the bottom discontinuity during the dynamic shear process, demonstrating that this testing system can observe the dynamic shear rupture without the undesired friction. The slip displacements of these two discontinuities are rate-dependent, and the normal stresses effect on the displacement field of these two faults is revealed. Therefore, the proposed dynamic double-direct shear experimental methodology can quantitatively observe the dynamic shear and slip process of faults. This system can be extended to investigate other dynamic responses of faults under complex stress states.