Experimental analysis and modeling of the mechanical behavior of breccia lava in the dam foundation of the Baihetan Hydropower Project

As a type of pyroclastic rock, the breccia lava in the dam foundation of the Baihetan Hydropower Project is characterized by relatively low density, high natural moisture content and porosity, and lower ultrasonic velocity. When it is used as a bearing rock, its mechanical behavior will be critical for the safety and stability of the world’s second largest hydropower station. Therefore, uniaxial and triaxial compression tests were performed to study the mechanical behavior of the breccia lava and scanning electron microscope (SEM) tests were carried out to reveal the microscopic failure modes of this rock. The experimental results indicated that all critical stresses, including the crack initiation stress (σ_ci), crack damage stress (σ_cd), and peak stress (σ_p), exhibit strong dependence on the confining pressure. Experiential functions were used to describe the evolution of the elastic modulus and Poisson’s ratio with confining pressure. Grain crushing and the growth and frictional sliding of microcracks were determined to cause the failure of the specimens. Based on the experimental results, a coupled elastoplastic damage model was proposed within a thermodynamic framework. In this model, two separate loading functions were employed to describe the damage and plasticity behavior of the breccia lava. A computational integration algorithm with high numerical accuracy and efficiency was developed to deal with the material under three different loading conditions: plasticity, damage, and coupled elastoplastic damage. The model was validated through comparison with the experimental data, and the good agreement between the two datasets confirms that the model can provide a good representation of mechanical behavior, particularly the post-peak behavior of the breccia lava.