Key Takeaways & Executive Findings
- •• Mechanical parameters of composite jointed rock masses exhibit pronounced anisotropy, with minimum elastic modulus and peak strength at a joint dip angle of 60°. • Increasing joint roughness reduces anisotropy and enhances energy storage capacity, with a strong linear relationship between elastic strain energy and peak deviatoric stress. • Joint dip angle controls the transition of dominant microcrack types from tensile to shear and back to tensile, as revealed by discrete element simulations. • Higher joint roughness suppresses damage localization along joints and increases the proportion of shear microcracks within the matrix by approximately 20%.
Abstract
Joints are widely distributed structural defects in rock masses, and their geometric characteristics play a decisive role in the overall stability of rocks under complex stress conditions. To clarify the influence of joint geometry on the mechanical behavior of jointed rock under such conditions, this study investigated the mechanical properties and failure mechanisms of composite jointed rock specimens with varying joint roughness and joint dip angles. Three typical failure modes under triaxial loading were identified, and a mechanical analysis model incorporating joint roughness and dip angle was established. The failure mechanism was revealed, and a discrete element model was developed to analyze the micro-damage evolution process of the specimens. The results show that the mechanical parameters of the specimens exhibit pronounced anisotropy. Both the elastic modulus and peak strength reach their minimum values at a joint dip angle of 60°. Increasing joint roughness significantly reduces the degree of anisotropy and enhances the energy storage capacity of the specimens. A strong linear relationship is observed between the elastic strain energy and the peak deviatoric stress, confirming the applicability of the linear energy storage law in composite jointed rocks. Discrete element simulations revealed the evolution path and dominant types of microcracks between the joint and matrix. The joint dip angle governs the transition of dominant crack types from tensile to shear and then back to tensile. Increased joint roughness significantly suppresses damage localization along the joint and results in an approximately 20% increase in the proportion of shear microcracks within the matrix. These findings clarify the regulatory role of joint geometrical parameters in the damage evolution process.
1. Introduction
In geotechnical and mining engineering, the stability and bearing capacity of rock masses are key factors in design and construction. Joints, as a common type of defect, are widely distributed within rock masses [1], significantly altering their mechanical properties [2,3] and increasing the likelihood of instability and failure. Composite jointed rock masses are commonly encountered in complex geotechnical engineering scenarios such as deep roadways, cross-lithological tunnels, high and steep slopes, and underground mines, as shown in Fig. 1. During deep excavation, such rock masses are typically subjected to a three-dimensional stress field comprising self-weight stress, horizontal tectonic stress, and mining-induced additional stress [4–6]. Their failure modes are significantly influenced by joint dip angle and joint roughness [7]. Specifically, during loading, rough joint surfaces generate shear friction, which promotes crack initiation at the joint tips; these cracks propagate and coalesce, eventually forming shear bands.
Numerous engineering practices have shown that composite jointed rock masses are prone to localized large deformations during construction, potentially leading to global instability of the rock mass and greatly increasing construction risk [8–10]. Therefore, understanding the failure mechanisms of composite jointed rock masses under triaxial conditions remains a key challenge in related research fields.
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Yao Bai, Zhibo Xu, Haoyu Dou, Nianzeng Liu, Ziyue Zhao, Sihao Qiu, Renliang Shan (2025). Study on mechanical properties and mesoscopic damage mechanism of composite jointed rock masses. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2025.08.018
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Frequently Asked Questions
What are the typical failure modes of composite jointed rock masses under triaxial loading?
The study identified three typical failure modes under triaxial loading, which are influenced by joint dip angle and roughness. These modes include tensile, shear, and mixed tensile-shear failures, with the dominant mode transitioning based on joint geometry.
How does joint dip angle affect the mechanical properties of composite jointed rock masses?
Joint dip angle significantly influences the mechanical properties, with both elastic modulus and peak strength reaching minimum values at a dip angle of 60°. This indicates pronounced anisotropy in the mechanical response.
What is the effect of joint roughness on the energy storage capacity of composite jointed rock masses?
Increasing joint roughness enhances the energy storage capacity of the specimens and reduces the degree of anisotropy. A strong linear relationship exists between elastic strain energy and peak deviatoric stress, confirming the linear energy storage law.
How does joint roughness influence microcrack evolution in composite jointed rock masses?
Higher joint roughness suppresses damage localization along the joint and increases the proportion of shear microcracks within the matrix by approximately 20%. This alters the dominant crack types and the overall damage evolution process.
What methods were used to analyze the mesoscopic damage mechanism?
The study employed discrete element modeling to simulate micro-damage evolution, revealing the evolution path and dominant types of microcracks between the joint and matrix. This approach provided insights into the regulatory role of joint geometrical parameters.
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