Mechanical and Permeability Characteristics of Basalt During Unloading Confining Pressure Creep Tests Under Coupled Hydro-Mechanical Conditions

This paper presents an experimental study on the mechanical behavior and permeability evolution of basalt, drilled from the dam foundation of the Baihetan Hydropower Station in China. Two groups of triaxial unloading creep tests under hydro-mechanical coupling conditions were conducted. Based on the experimental results, creep deformation and failure characteristics of basalt were investigated. It was found that the relationship between the confining pressure and steady creep rate could be described satisfactorily by an exponential function. A tensile-shear failure mode was observed for basalt under the action of unloading confining pressure and hydraulic-mechanical coupling. The permeability evolution of basalt in the unloading creep process exhibited phased characteristics: permeability decreased in the initial loading phase and remained stable for a certain range of confining pressure in the steady creep phase. Exponential functions were also used to describe the evolution of permeability and confining pressure. The results of this study can provide a comprehensive understanding for the long-term stability assessment of basalt under coupled hydro-mechanical conditions.