Experimental study on seepage-stress coupling failure characteristics and fracture fractal characteristics of cemented gangue-fly ash backfill with defects

In order to study the seepage-stress coupling failure characteristics and fracture fractal characteristics of cemented gangue-fly ash backfill (CGFB) with defects, the samples of single crack CGFB with different angles were prepared and the triaxial compression test under seepage conditions was carried out. The effects of seepage pressure and crack defects on the seepage-stress coupling failure characteristics of CGFB were analyzed. In addition, the box dimension method was introduced to calculate the fractal dimension, so as to quantitatively characterize the correlation between fracture morphology and mechanical properties. The results show that: 1) the permeability and acoustic emission change periodically with the stress-time curve during the deformation and failure of CGFB. With the increase of seepage pressure, the characteristic permeability of CGFB increases, and the characteristic permeability of CGFB with defects is higher than that of intact CGFB. 2) Under the seepage -stress coupling, there is no obvious corresponding relationship between the fractal dimension of fracture appearance and the compressive strength of CGFB: under the same seepage pressure, the higher the strength of CGFB with different angles, the greater the fractal dimension of fracture appearance; under the same crack angle, the greater the seepage pressure, the lower the strength and the larger the fracture fractal dimension. 3) Under the seepage-stress coupling, the fractal dimension of the failure fracture appearance has a good correlation with the dissipated energy, and the two increase linearly. This relative relationship is only related to the damage and fracture, and has nothing to do with the external conditions such as seepage pressure. The research results provide a theoretical basis for the stability analysis and instability prediction of artificial pillar containing joints, cracks and other geological defects under water-rich conditions in China.