Abstract:

To investigate the impact of cyclic loading on the mechanical damage characteristics and seepage evolution of fractured rock mass, the stress-seepage coupling tests were conducted on sandstone samples containing an inclined rough single fracture under conditions of axial and pore pressures low frequency repeatedly loading and unloading. The results indicate that under stress, rock samples exhibit relative slip along pre-existing fractures, with surface protrusions undergoing wear and shear. These protrusions cause a slight stress drop during loading, leading to flow rate fluctuations during compression. For samples with inclined fractures, strength is mainly determined by slip along pre-existing fractures and pore pressure magnitude. During cyclic loading and unloading under axial compression, fractured rock mass undergoes progressive damage and deterioration with increasing cycles. This reduces the samples’ ability to resist deformation. Additionally, samples exhibit a nonlinear decrease in elastic modulus and a nonlinear increase in Poisson’s ratio with increasing cycles. Pore pressure cycling shortens the decay creep stage and reduces strain rates in the stable creep stage. The flow rate dynamically evolves during cyclic loading and unloading. Initially, the flow rate decreases due to fracture closure under stress. Subsequently, it decreases and then increases with cyclic axial stress. The grayscale threshold segmentation method effectively separates connected and contact zones of fractures. It shows that final flow increases exponentially with increases in fractal dimension D and connection ratio Φ.

Key words: fractured rock mass, cyclic loading and unloading, mechanical properties, seepage, morphological characterization