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Abstract
This study numerically investigates contact forces and the contact network in unconfined and confined compression tests on rock-like bonded granular materials using the particle-based discrete element method (DEM). Statistical analysis of contact force magnitudes and polar distributions under varying confining pressures reveals a significant influence of confining pressure on force evolution. Additionally, contact force distribution is closely related to internal structures and external loads. The relationship between contact force and geometrical features of the contact network is analyzed, along with the three-stage evolution of the relationship between force anisotropy and stress ratio, driven by contact network changes. Tensile force chain lengths follow an exponential distribution. Without confinement, tensile force chains remain stable until crack formation, whereas under confinement, they increase in number and length before decreasing due to the occurrence of cracks. Higher confinement results in shorter, fewer tensile force chains. Finally, the number, orientation and force magnitude of new tensile contacts are analyzed to further elucidate tensile contact evolution in bonded granular materials.
Highlights
discrete element method (DEM) simulations of compression tests under varying confining pressures were conducted to investigate the effects of confinement on internal force transmission and structural evolution in bonded granular materials
The main findings are summarized as follows: Under confined compression, a compression–to–tensile transition develops during loading, accompanied by increased force anisotropy
The magnitude distribution of contact forces is related to contact network geometry and evolves with loading
Summary
Rock stability is a major concern in geological and engineering applications such as tunneling, mining, and reservoir engineering (Wang et al 2000; Hajiabdolmajid and Kaiser 2003; Zhang et al 2014). Since rock consists of bonded mineral grains, its mechanical behavior is governed by microscale interactions. Understanding these interactions is essential for analyzing stress distribution, fracture initiation, and failure mechanisms. In DEM, rock is modeled as an assembly of bonded particles, where interparticle contacts form through overlap. The distribution of contact forces in unbonded granular materials has been well studied (Kruyt and Rothenburg 2004; Majmudar and Behringer 2005). Bond breakage occurs once the strength limit is exceeded, resulting in a rapid redistribution of contact forces and distinct evolutionary characteristics. While some studies have explored this topic, research on contact force evolution in bonded granular materials remains limited and lacks detailed analysis
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