Loading rate dependency is one of the significant time-dependent behaviors of rock and rock discontinuities. To investigate the shear rate– dependent behavior of the shear strength of discontinuities with different joint roughness coefficients (JRCs), direct shear tests with various shear rates were conducted on samples with artificial joint surfaces based on Barton’s standard profile lines. A new test method, called shear test with alternate shear rates, was introduced to verify the direct shear results, and a JRC weakening model was established to explain the mechanism of shear rate dependency of discontinuities and the influence of the JRC on shear rate dependency. Results revealed that the shear strength increased with an increase in shear rate and the shear rate dependency of discontinuities was significantly influenced by surface morphology. Hence, the greater the JRC is, the stronger the shear rate dependency will be. Results also demonstrated that the direct shear test is the process of the JRC resistance weakening and frictional resistance strengthening, and the shear rate dependency was caused by the time-dependent behavior of the crack growth.

An experimental investigation on chloride diffusion in structural concrete under the cyclic impact loading is conducted. Effects of magnitudes and loading times are studied. Relationship between damage coefficients and chloride diffusion coefficients is obtained. The cyclic impact loading causes the initiation of new cracks and the propagation of existing cracks, which brings an obvious promotion for chloride diffusion. There should be a damage threshold. If the magnitude of the external loading is large enough to make the damage exceed the threshold, initiation and propagation of cracks become quite significant and chloride diffusion can be greatly promoted. With the increase of the damage coefficient, the chloride diffusion coefficient increases. The increasing rates decrease with long immersion times. Relationship curves of damage coefficients and chloride diffusion coefficients show a good correlation and can be well described with power functions.