Earthquake is caused by the varying crustal stresses and it is a product of rock fracturing and/or slippage of major discontinuities such as faults and fracture zones. Therefore, the shear response of rock discontinuities has a direct relevance to the mechanism of earthquakes and their source characteristics as well as their effect on rock engineering structures. In this study, despite some difficulties, the author would propose a general procedure to simulate shear loads in direct shear tests of discontinuities and interfaces due to ground motions caused by earthquakes. Furthermore, dynamic direct shear testing devices are very few worldwide and the utilization of shaking tables for dynamic direct shear testing of rock discontinuities and interfaces as an alternative is proposed. This procedure is applied to the direct shear tests of several artificial and natural rock discontinuities and interfaces. The experimental results are presented and the outcomes of this study are discussed in the field of rock dynamics.
Rock dynamics has become one of the most important topics in the field of rock mechanics and rock engineering (e.g., Aydan, 2017; Zhou and Zhao, 2011; Iwata et al. 2016, 2017, 2018). Varying crustal stresses cause earthquakes and rock fracturing and/or slippage of major discontinuities such as faults and fracture zones occur. Therefore, the shear response of rock discontinuities is of great importance in regard with the mechanism of earthquakes and their source characteristics as well as their effect on rock engineering structures.
Dynamic direct shear testing is a relatively new field of experimental research and there are no well-established procedures yet. However, the shear loading procedures must be based on the strong motion records taken during earthquakes. If the shear loading on rock discontinuities due to actual earthquakes is to be considered, the displacement response must be used as the frequencies of accelerations are extremely difficult to simulate in available equipments. However, as shown by Aydan and Ohta (2011) or Aydan et al. (2011), the displacements are in the order of meters, no shear testing device available in the world can impose such displacement records on the samples. Furthermore, there is an issue of wave propagation through rock mass during the shaking induced by earthquakes, which should be carefully considered in this respect.