During the construction of tunnels in the central and western regions of China, diorite is frequently affected by vibration, blasting and water which will lead to the questions of the quality and operational safety of project. However, there are few studies on the dynamic characteristics of diorite under the action of dry-wet cycles. Therefore, this paper selected the gray-green altered diorite from Ning shan County, Shaanxi Province, China, mainly composed of plagioclase, and used the Slit Hopkinson pressure bar (SHPB) to study the effect of dry-wet cycle on the dynamic characteristics of Diorite. The test results show that the strength decay rate of the peak strength of diorite is the maximum under 1-3 dry-wet cycles, then decreases gradually. The dynamic elastic modulus of diorite dropped by 35.02% after three dry-wet cycles, accounting for 98.45% of the total attenuation. Compared the test result of three dry-wet cycles, the decrease volumes of the stress growth rate of diorite are the largest after six dry-wet cycles. Because of the actions of the dry-wet cycles, the growth rate of the rapid growth stage of the reflected energy-time history curve reduces and the growth rate of the rapid growth stage of the transmitted energy-time history curve improves. Under the action of the dry-wet cycles, the dissipation energy ratio gradually decreases, and the decrease of energy consumption density follows a negative exponential function relationship. Under the action of multiple dry-wet cycles, the tension and compression stress frequently change between the particles of rock, resulting in a significant increase of micro-cracks and an obvious degradation effect on the dynamical properties of diorite. KeywordsDry-wet cycle • Hopkinson pressure bar test • Dynamic uniaxial compressive strength • Dynamic elastic modulus • Stress growth rate • Energy analysis * Jiangbo Xu

In order to explore the fracture mechanism of jointed Phyllite, the TAJW-2000 rock mechanics test system is used to carry out uniaxial compression tests on different joint inclination Phyllites. The influence of joint inclination of Phyllite failure mode is discussed, and the progressive failure process of Phyllite is studied. The test results show that the uniaxial compressive strength anisotropy of jointed Phyllite is remarkable. As the inclination increases, it exhibits a U-shaped change; When 30° ≤ α ≤ 75°, the tensile and shear failures along the joint inclination mainly occurs. the joint inclination controls the failure surface form of the Phyllite; The crack initial stress level of the joint Phyllite is 0.30–0.59σf, the crack failure stress level is 0.44–0.86σf. When α = 90°, the σcd value is the largest, and σcd with α = 90° can be used as the maximum reliable value of uniaxial compressive strength of Phyllite. Using the theory of fracture mechanics, it is analyzed that under uniaxial compression of the rock, the crack does not break along the original crack direction, but extends along the direction at a certain angle to the original crack. The joint effect coefficient is proposed to show the influence of the joint inclination on the uniaxial compressive strength of the phyllite. Both the test and simulation results show that when the joint inclination is 60°, the joint effect coefficient is the largest. The compressive strength is the smallest. Numerical simulation analyses the crack evolution law of phyllite under different joint inclination under uniaxial compression, which verifies that there are different failure modes of joint phyllite under uniaxial compression.

The acoustic wave test was carried out by selecting the joints of the joint surface and the horizontal plane at 0°, 30°, 45°, 60°, 75°, and 90° phyllite samples. According to the corresponding waveform diagram, the starting point is selected, and the dynamic deformation parameters of thousands of rock samples under various angles are calculated. The results show that: The anisotropy characteristics of the dynamic deformation parameters are obvious, and the influence of the variation of the joint surface inclination on the dynamic deformation parameters is achieved by affecting the wave impedance. P-wave impedance and S-wave impedance have different effects on rock dynamic deformation parameters. Generally, P-wave and S-wave impedance should be considered comprehensively for the dynamic deformation parameters of rock samples. Acoustic waves are in the elastic deformation law of the rock sample caused by the propagation in the rock sample is similar to the elastic deformation law caused by the external load acting on the rock sample.