On the effective stress coefficient of single rough rock fractures

The effective stress coefficient is critical to accurately predict the hydromechanical coupling behavior of single water-bearing rock fractures. The physical meaning of the effective stress coefficient in a rough rock fracture is understood as the ratio of the nominal fracture surface occupied by water to the total fracture surface area. To overcome the difficulty of measuring contact ratio changes in rough rock fractures under normal loading and water pressure, a new effective stress coefficient model for single rough water-bearing fractures is proposed in terms of two mechanical parameters, initial normal stiffness and maximum normal closure. By incorporating the new effective stress coefficient model into the Barton-Bandis constitutive model, a hydromechanical coupling model was built and verified by laboratory and in-situ experimental data. The results indicate that the effective stress coefficient is less than 1 for single rough rock fractures and decreases with increasing difference between normal stress and water pressure. When the normal stress is close to or considerably higher than the fracture water pressure, both the newly built model and Terzaghi's model obtain similar normal displacement. However, for moderate normal stress, the normal displacements predicted by the newly built model and Terzaghi's model differ significantly. The implications of the newly built model in subsurface engineering are discussed.

Automated summary

The effective stress coefficient is crucial for predicting hydromechanical coupling behavior in water-bearing rock fractures. A new model based on the ratio of water-covered fracture surface to total area was proposed and successfully integrated into a constitutive model, showing that the coefficient is less than 1 and decreases with increasing stress-water pressure difference. The new model yielded similar results to Terzaghi's model at high stress levels but differed significantly at moderate stress levels, with implications for subsurface engineering.