Influence of loading rate on the deformation characteristics of single-fracture rock-like models

The deformation behavior of fractured rock masses is often a key factor causing instability of engineering rock masses and frequent geological disasters. The complex changes in the load acting on engineering rock masses can trigger and alter the mechanical response processes such as deformation and fracture of the rock masses. This study employs physical simulation techniques to replicate the behavior of real rock masses through the use of rock-like models. Specifically, single-fracture rock-like specimens with consistent characteristics are fabricated utilizing river sand, cement, gypsum, and putty powder. Uniaxial compression tests are subsequently conducted on these specimens to examine the impact of loading rate on their deformation behavior. The primary focus lies on the sliding deformation patterns exhibited by the media on either side of the fractures, as well as the fracture behaviors associated with the pre-existing fractures. To monitor the deformation evolution processes both internally and externally within the models, embedded strain rosettes and digital image technology are concurrently employed. This approach facilitates an exploration of the influence of loading rate on the deformation characteristics at the fracture tips and the fracture behaviors observed on the model surface. The results show that: (1) With the increase of loading rate, the failure mode of the model transforms from ductile to brittle, reflecting the differences in the adjustment mode of rock mass bearing structure under different loading rates. (2) The initiation time of strain localization is independent of the rate, and as the loading rate increases, the strain deflection angle of the tension and compression stress zones in the model changes from asynchronous oscillation to synchronous oscillation. (3) At low loading rates, the failure mode of the model is stable. As the loading rate increases, the failure mode becomes more complex, and the surface crack density increases. When the loading rate exceeds a certain threshold, the failure mode of the model changes to "X-shaped" shear failure. (4) There is a significant correlation between the sliding rate of the fracture and the deflection angle of the principal strain at the end, reflecting the coupling effect of rock mass damage and strain field evolution under Griffith's criterion.