A New Dynamic Direct Shear Testing Device on Rock Joints

Appendix

To elaborate the key technique of “cyclic loading”, an example of cyclic shear test results of the granite joint with the specimen length of 1000 mm (along shear direction), the width of 250 mm and the height of 300 mm under the CNL condition is shown in Fig. 7. The granite joint has the regular sawtooth shape with five identical and isosceles saw teeth, and each one possesses the undulated angle of 13°, the height of 23.09 mm as well as the length of 200 mm, as depicted in Fig. 7a. Fig. 7b–d illustrate the load-displacement-time relations of the cyclic shear test results of the granite joint. From Fig. 7b, c, it can be found that there are three cyclic shear processes, where the shear rate and the normal load remain constant at values of 1 mm/s and 25 kN, respectively, which reveals the reliability of the “cyclic loading” technique. In Fig. 7b, c, it shows that the shear loading amplitude and the frequency are 30 mm and 0.0083 Hz, respectively. It indicates that the shear resistance (the peak shear load) in both the forward positive and backward positive shear processes decreases slightly from the first cycle to the third cycle, as depicted in Fig. 7b, d.

To give a detailed description of the key technique of “CNS loading”, an example of shear test results of the granite joint with the specimen length of 200 mm (along shear direction), the width of 100 mm and the height of 150 mm under the CNS condition is depicted in Fig. 8. The granite joint has the tilted flat and straight shape with the inclination angle of 14°, as shown in Fig. 8a. Fig. 8b–d illustrate the load-displacement relations of the shear test results of the granite joint under the CNS condition. According to Fig. 8b, c, it can be found that in CNS tests with the k_n of 0, i.e., CNL tests, the normal load retains constant at the value of 10 kN with the increase of the normal displacement and the shear displacement. In comparison with the k_n of 1.56 kN/mm and 3 kN/mm of CNS tests, the normal load and the normal displacement are well proportioned with the normal displacement increasing at different shear rate values of 0.1 mm/s and 1 mm/s, which reflects the reliability of the “CNS loading” technique. It indicates that the joint shows an elastic-plastic behavior in CNL tests, while the shear load increases gradually with the shear displacement increasing in CNS tests (k_n = 1.56 kN/mm and k_n = 3 kN/mm), as depicted in Fig. 8d.