Study on the mechanical behavior and energy characteristics of rocks with closed cracks based on combined finite-discrete element method

Abstract

Many serious catastrophes are caused by complex cracks naturally distributed in rock masses. Understanding the mechanical behavior and energy evolution of rocks with closed cracks in different geometrical properties is crucial. This study presents a comprehensive investigation into the influence of crack inclination, length, and location on mechanical behavior, damage characteristics, and energy evolution in rocks. The findings demonstrate that the closed cracks significantly alter the stress–strain. The peak strength and elastic modulus exhibit an asymmetric U-shaped variation with increasing crack angle, decreasing quadratically with increasing crack length, and the crack location also affects the mechanical properties. Furthermore, the inclination angle and location of closed cracks considerably affect the damage characteristics. Cracks near the upper boundary of the specimen are less likely to propagate. Regarding energy evolution, this study presents a novel method using the residual energy index to assess the impact characteristics. The residual energy index initially decreases and then increases with increasing crack inclination. The residual energy index initially decreases and then stabilizes as the crack length increases, with the critical crack length identified as 15 mm. These findings provide a theoretical foundation for understanding dynamic hazards and determining the relevant hydraulic fracturing parameters.