In hard rock, many rock discontinuities such as bedding plane, joint, fissure et al. are distributed, and influence the strength and deformability of rock mass. In Japan, after the 2011 off the Pacific coast of Tohoku Earthquake, a new method of dynamic analysis for discontinuous rock mass has been proposed. The dynamic strength and deformability of rock discontinuity which used as the input parameters are very important in this analysis.
The authors have developed a new dynamic load-testing machine, for the purpose of investigating the response to the earthquake motion of rock discontinuities. This test machine is a direct shear test machine of the shear-box type, and makes it possible to perform load-testing of cyclic shear stress ±50kN and positive normal stress ±50kN. Both dynamic direct shear tests and the dynamic normal deformation tests are also possible. The control system makes it possible to change the parameters such as cyclic numbers of loading, stress amplitude, frequency of loading wave and type of loading wave.
This paper reports on the dynamic shear deformability and strength of rock discontinuities under dynamic direct shear testing. We performed 2 types of dynamic direct shear tests on rock discontinuities. One is the Multi-stage amplitude dynamic direct shear test, as carried out usually on intact core specimens. The other was Increase amplitude dynamic direct shear test that we had previously proposed. The Increase amplitude dynamic direct shear test involves progressively increases loading of the cyclic shear stress amplitude.
Test specimens were natural rock discontinuities sampled from bored-cores and artificial discontinuities made by mortar. From these tests results, the dynamic shear strength exceeds the static shear strength for rough natural rock discontinuity. However, the clear difference is not recognized among both for flat natural rock discontinuity.
