Intermittent jointed rocks, widely existing in various mining and civil engineering structures, are quite sensitive to dynamic cyclic loading conditions. Understanding the dynamic mechanical properties of jointed rocks is beneficial for the rational design and the long-term stability assessment of rock engineering projects. This study experimentally investigates the dynamic mechanical properties of synthetic jointed rock models under different cyclic conditions, regarding four loading frequencies, four maximum stresses and four amplitudes. Our experimental results reveal the influence of the three cyclic loading parameters on the mechanical properties of jointed rocks, including the fatigue deformation characteristics, the fatigue energy and damage evolution, and the fatigue progressive failure behavior. Under lower loading frequency or higher maximum stress and amplitude, the jointed rock is characterized by higher fatigue deformation moduli and higher dissipated hysteresis energy, leading to higher accumulative damage and lower fatigue life. The accumulative fatigue damage of jointed rocks exhibits an inverted S-shape with a three-stage evolution, i.e., initial, steady and accelerated stage. The fatigue failure modes of jointed rocks are independent of cyclic loading parameters; all tested jointed rocks feature a prominent tensile splitting failure mode. Three different crack coalescence patterns are classified between two adjacent joints. Furthermore, different from the progressive failure under static monotonic loading, the jointed rocks under cyclic compression fail more abruptly without evident preceding signs. The tensile cracks on the front surface of jointed rocks always initiate from the joint tips, and then propagate at a certain angle with the joints towards the direction of maximum compression.


The mechanical characteristics of intermittently jointed rocks play a dominant role in the overall mechanical behavior of many mining and civil engineering structures, such as underground tunnels, bridge abutments and road foundations. Since these rock structures are likely to be subjected to cyclic loading resulting from earthquakes, quarrying and rockbursts, it is thus crucial to characterize the fatigue properties and failure mechanism of intermittently jointed rocks for the rational design and long-term stability analysis of rock structures under different cyclic loading conditions.

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