Analysis of failure characteristics and constitutive model development for sandstone with different ligament angles under biaxial loading based on infrared radiation

Abstract

The instability and failure mechanisms of engineering rock masses are significantly influenced by fissures, increasing their uncertainty. Under the action of a lateral constraint load, the bearing characteristics and deformation behavior of rock masses become more complex. To investigate the impact of the ligament angle on failure mechanisms and provide precursor information for rock instability, this study conducted biaxial compression experiments on pre-cracked sandstones with varying ligament angles. Infrared thermal imaging (ITI), acoustic emission (AE), and digital image correlation (DIC) were employed. The results indicate the following: First, pre-cracked sandstone samples with different ligament angles exhibited variations in elastic modulus and strength. However, under lateral load constraints, these variations were minimal, and the failure mode demonstrated ductile characteristics. As the ligament angle increases, the crack coalescence mode transitions from the shear crack coalescence mode to the tension-dominated tensile-shear mixed mode. Second, a predictive infrared radiation-based index, the difference in average infrared radiation temperature (DIRT), was proposed to monitor the evolution of rock damage. The rate of change in the DIRT can be divided into three phases: the “steady phase–accelerated growth phase–rapid growth phase,” corresponding to different stages of damage development during rock loading. Finally, a damage variable was defined on the basis of the DIRT, and a damage constitutive model for rock was established. The model’s computational results closely match the experimental curves, validating the rationality of the defined damage variable.