Fracturing and acoustic emission characteristics of saturated reservoir rocks under constant-amplitude-cyclic loading

To investigate the fracture behavior of slope rock masses under reservoir water fluctuation, several groups of constant-amplitude-cyclic loading tests and acoustic emission (AE) tests were conducted on two types of sandstone rocks, i.e., red sandstone and cyan sandstone, under both dry and saturated conditions. The variation in mechanical parameters, failure pattern and AE characteristics with water saturation and cyclic loading were systematically explored. The laboratory results show that water saturation causes: i) a notable reduction in peak stress (53.98% for red sandstone and 20.70% for cyan sandstone); ii) a considerable increase in failure strain (8.03% for red sandstone and 13.27% for cyan sandstone); iii) an elevated level of AE activity during cyclic loading phase; and iv) a significant enhancement in the occurrence of tensile failure. The statistical analysis of experimental AE waveform data demonstrates a discernible clustering of AE waveforms with low dominant frequency (L-type waveform) and those with high dominant frequency (H-type waveform). Dry rocks under cyclic loading exhibit the prevailing dominance of H-type waveforms, while saturated rocks display a shift towards the predominance of L-type waveforms. Moreover, both water saturation and cyclic loading contribute to the occurrence of L-type waveforms, which are closely associated with tensile failure in rocks. Based on this, cyclic loading is believed to substantially accelerate strength degradation and catastrophic fracture of rocks. Fracturing and AE characteristics investigated in this work likely shed light on accessing the stability of reservoir slopes experiencing recurrent external loads.