The friction strength evolution of rock joints subjected to cyclic dynamic loads is very vital to the safety and stability assessment of rock engineering during earthquakes and rock bursts. In this paper, cyclic shear experiments under different normal stress were carried out for granite joints based on a shaking table apparatus. The frictional behavior under cyclic shear, especially the dynamic evolution of friction strength, was investigated and the effect of normal stress on friction strength weakening was quantified. Based on experimental results, a hysteresis model is used to characterize the dynamic friction behavior of planar joints under cyclic shear. This model relates the evolution of friction strength to the number of cycles of cyclic shear. As the normal stress increases, the strength weakening ratio increases correspondingly, while the critical number of cycles (at which the residual strength is reached) remains essentially unchanged.
The safety of many rock engineering projects is strongly affected by complex geological formations, especially joints and faults. Due to the excitation of seismic waves, the rock joints bear dynamic loads in addition to static loads, which will lead to cyclic fatigue damages (e.g. Liu et al. 2018 and He et al. 2021). Hence, it is crucial to develop a fundamental understanding of the strength evolution behavior of rock discontinuities under dynamic cyclic loading, which can be simulated as cyclic shear along the rock joint (Niktabar et al. 2017).
Many researchers have studied the frictional strength under dynamic cyclic loading conditions. The effect of frequency on the shear strength under dynamic cyclic loading was analysed by Ahola et al. (1996) and Ferrero et al. (2010). They found that the shear strength decreases as the number of cycles increases. Dang et al. (2020) conducted dynamic cyclic experiments on planar joints and revealed that the coefficient of friction changed cyclically with a change in the shear direction. Zhang et al. (2023) experimentally investigated the effect of cyclic shear loading on the frictional properties of a typical granite specimens and proposed a phenomenological model to describe the influence of loading frequency on the frictional strength weakening.
