The Impact of Shear Rate on the Mechanical Behavior of Rock Joints Under Multiple-Influencing Factors

The shear rate is an important factor that influences the shear mechanical properties of rock joints. In this paper, constant normal load (CNL) direct shear tests at different shear rates (v(s) = 0.2-5.0 mm/min) were performed on rock joint specimens to investigate the shear behavior and failure modes under various joint roughness coefficients (JRC = 6.071-17.212), joint wall compressive strengths (JCS = 9.36-25.86 MPa), and normal stresses (s(n) = 0.936-2.586 MPa). The experimental results indicated that the peak shear strength gradually decreased, the peak shear displacement increased and the residual shear strength decreased with increasing shear rate. The experimental findings suggested that with an increasing JRC and a decreasing JCS and s(n), the peak shear strength and peak shear displacement were greatly influenced by the shear rate. Additionally, shear-off and wear failure modes were observed in this research and were both intensified by increasing shear rates. However, the failure mode tended to change from wear to shear-off as the shear rate increased, and this phenomenon was enhanced when JRC, JCS, and s(n) decreased. A modified new shear strength correlation model that related v(s) and valid values of JRC, JCS, and s(n) was developed to estimate the shear strength of rock joints. The predicted results indicated that the newly proposed model performed better than the existing models.

Automated summary

The shear rate has a significant impact on the shear mechanical properties of rock joints. This study conducted constant normal load direct shear tests on rock joint specimens under different shear rates to investigate their behavior and failure modes. The results showed that higher shear rates led to a decrease in peak shear strength, an increase in peak shear displacement, and a decrease in residual shear strength. The study also observed that increasing joint roughness coefficients and decreasing joint wall compressive strengths and normal stresses intensified the influence of shear rate on peak shear strength and peak shear displacement. Moreover, the research identified shear-off and wear failure modes, both of which were intensified by higher shear rates. However, as the shear rate increased, the dominant failure mode transitioned from wear to shear-off, especially when joint roughness coefficients, joint wall compressive strengths, and normal stresses decreased. Lastly, the study proposed a modified shear strength correlation model that incorporated shear rate and relevant variables to estimate the shear strength of rock joints. The predicted results demonstrated that the newly proposed model outperformed existing models.