Abstract
To better understand the evolution of crack propagation in brittle rock mass, the particle velocity field evolution on both sides of secondary crack in rock-like materials (cement mortar specimens) with pre-existing parallel double flaws under uniaxial compression is analyzed based on the discrete element theory. By bringing in strain rate tensor, a new technique is proposed for quantifying the failure mechanism of cracks to distinguish the types and mechanical behaviors of secondary cracks between pre-existing parallel flaws. The research results show that the types and mechanical behaviors of secondary cracks are distinct at different axial loading stages and can be directly identified and captured through the presented approach. The relative motion trend between particles determines the types and mechanical behaviors of secondary cracks. Based on particles movement on both sides of secondary cracks between cracks, the velocity fields of particles can be divided into four types to further analyze the causes of different types of cracks. In different axial loading stages, the velocity field types of particles on both sides of cracks are continuously evolving. According to the particle velocity field analysis and the proposed novel way, the types of macroscopic cracks are not directly determined by the types of dominated micro-cracks. Under uniaxial compression, the particles between secondary cracks and pre-existing parallel flaws form a confined compressive member. Under the confinement of lateral particles, secondary cracks appear as shear cracks between pre-existing parallel flaws at the beginning stage of crack initiation.
Highlights
Fractured rock mass is one of the most significant construction objects encountered in geotechnical engineering
A large number of experimental works are available on crack propagation and failure mode from pre-cracked brittle rock-like materials under uniaxial compression [6,7,8,9,10]
To further gain insight into the mechanism of secondary crack propagation, we proposed a technique to quantify the failure mechanism of secondary crack at different loading stages by means of adopting strain rate tensor analysis
Summary
Fractured rock mass is one of the most significant construction objects encountered in geotechnical engineering. A large number of experimental works are available on crack propagation and failure mode from pre-cracked brittle rock-like materials under uniaxial compression [6,7,8,9,10]. Based on the moment tensor inversion analysis, Zhang et al [31] found that a large number of tensile micro-cracks appeared in the rock bridge area at the initial loading stage, and an obvious shear band formed due to the relative slip between the particles, indicating that the macroscopic shear fracture is not completely composed of shear micro-cracks. Based on the discrete element theory, we can obtain the strain rate tensor by arranging the measurement circle between pre-existing parallel flaws, and accurately define two variables to quantify the crack failure mechanism, providing a more efficient method to distinguish secondary crack types. R, it is convenient for us to distinguish crack types and reveal essential crack characteristics
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