Progressive failure and acoustic emission characteristics of bimodular rock materials under compression: A distinct element study

: Rock materials, as natural composites, inherently exhibit a pronounced tension-compression elastic asymmetry, termed bimodular behavior, where the tensile modulus ( E t ) is substantially lower than the compressive modulus ( E c ). Nevertheless, how this fundamental material attribute influences progressive failure and acoustic emission (AE) of rock under uniaxial compression remains unclear. To address this research gap, we develop an elastic asymmetric model (AM) alongside an elastic symmetric model (SM) within the discrete element framework. Relevant model parameters are calibrated through comparisons with laboratory uniaxial compression and direct tensile tests on Yunnan marble, and the moment tensor method is adopted to quantitatively characterize AE signals. We then systematically examine the effects of tension-compression elastic asymmetry on contact force and stress distributions, displacement field evolution, progressive failure process, and AE characteristics. Compared to the SM, the AM accurately reproduces the core mechanical responses of marble, including more heterogeneous contact force and stress distributions, enhanced lateral deformation, delayed microcrack initiation, directional microcrack propagation, and localized damage zones, accompanied by moderate AE activity and concentrated energy release. In contrast, the SM overestimates E t , which leads to insufficient development of stress, early-stage dispersed microcracking, non-localized damage, and more diffuse and higher-energy AE responses. These findings reveal the mechanism by which the E t / E c asymmetry governs micro-to-macro mechanical behaviors and AE characteristics of rock, emphasizing the critical importance of accounting for bimodular elasticity in geological materials mechanical analysis and providing a theoretical reference for rock burst monitoring and hazard mitigation in deep underground excavations.