Distinct element modelling of stress wave propagation in rock masses considering asymmetrical loading/unloading behavior of filled fracture: Unique compression-hardening and memory effect

Abstract

Dynamic loads like seismic and blasting waves, exhibit characteristics such as variable frequency, amplitude, and multiple cycles. These loads can induce cyclic loading and unloading of fractures in rock masses, progressively altering the mechanical properties of the fractures and affecting the propagation of stress waves. However, existing models are unable to capture the above process. Experimental investigations reveal filled fractures’ unique compression-hardening and memory effects under cyclic loading/unloading, characterized by asymmetric loading/unloading behaviors. To capture this characteristic, we developed a modified Barton-Bandis model in UDEC 7.0 that incorporates asymmetric loading/unloading (BBLU), successfully replicating the cyclic loading and unloading behavior of filled fractures. The simulation results of stress wave propagation in fractured rock masses with asymmetric loading/unloading behavior show that compressive stress waves lead to stiffness hardening of the fractures and suppress the attenuation of stress wave frequency. Notably, compression hardening and memory effects retain the stiffness hardening from previous loading/unloading cycles. Under the influence of multi-cycle waves, this results in cumulative deformation, enhancing the transmission capacity of stress waves. In multi-fractured rock masses, stress waves experience multiple reflections at the fractures, where the memory effect reduces the ability of the fractures to reflect stress waves and compresses the wavelength. This dual mechanism weakens the superposition of multiple reflected waves. These findings bridge theoretical models with real-world fracture mechanics, enhancing prediction of wave-driven damage progression and hazard mitigation in underground engineering-particularly under cyclic disturbances and complex fracture networks. This research redefines structural control evaluations for rock mass dynamics under multiparameter interactions, offering transformative insights for engineering safety optimization.