Effects of fracture filling ratio and confining stress on the equivalent effective stress coefficient of rocks containing a single fracture

Because fractures are ubiquitous in rock masses, the states of stress and fracture filling significantly impact the coupled hydromechanical behaviors of fractured rocks. Based on the effective stress principle of porous media, we developed a method to determine the equivalent effective stress coefficient of rocks containing a single fracture, and analyzed the impacts of fracture filling area ratio, confining stress, and pore pressure. Confining stress and pore pressure were applied sequentially onto rock specimens, and two bulk moduli were calculated based on the measured deformation during the loading process of confining stress and pore pressure. The equivalent effective stress coefficient was then determined as the ratio of the two bulk moduli. Our results show that the equivalent effective stress coefficient increases as the filling area ratio or confining stress decreases, or pore pressure increases. The difference in equivalent effective stress coefficient of specimens with two filling area ratios decreases as the confining stress increases. The effective stress coefficient of a single fracture is inherently considered to be the ratio of the nominal fracture surface occupied by water to the total fracture surface area. When the confining stress and filling ratio increases or the pore pressure decreases, the nominal fracture surface occupied by water decreases, resulting in the corresponding reduction of the equivalent effective stress coefficient. These results provide important insights into the coupled hydromechanical behaviors of fractured rocks.