Mechanical behaviors and damage constitutive model of pre-damaged and saturated granites under uniaxial compression.

Excavation disturbance and groundwater actions can lead to initial damage in granites, posing a long-term stability threat to underground structures. Due to the lack of quantification methods for initial damage, it is hard to investigate the mechanical characteristics of granites under the combined effects of the excavation-induced damage and the water-rock weakening damage. In this investigation, granite samples were saturated in water for one year and subjected to different pre-loading to induce various levels of initial damage using Damage Stress Ratio (DSR) method. Uniaxial tests, acoustic wave tests, and microscopic examinations were performed on granites to analyze their mechanical behavior. The key findings are as follows: (1) A novel constitutive model is proposed, capturing the combined influence of pre-loading and water-induced weakening as a damage variable. It accurately describes the stress-strain curves of granites under this combined action, including the void-compaction stage. (2) Granites experience transgranular failure along fish-scale-like joint planes, contributing to their low strength. A one-year saturation period results in a softening coefficient of 0.83 in this specific granite, which emphasizes the performance of water-induced degradation. Furthermore, escalating the initial damage variable results in a reduction in uniaxial compressive strength, axial strain at failure, and the volume expansion point, while instigating a gradual augmentation in lateral strain. (3) A linear direct correlation is observed between strength and P wave velocity in both saturated-for-one-year and dried granites. Additionally, a linear correlation is established between the initial damage variable and the Damage Stress Ratio (DSR). These findings provide valuable insights for the characterization and prediction of their strength and damage properties. [ABSTRACT FROM AUTHOR]