Failure mechanism and mesoscopic response of limestone with filled joints under triaxial stress

This study addresses the common structural defect of filled joints in limestone and investigates how the inward extension length of such joints affects the mechanical properties of the rock. Specifically, the intrinsic relationship among filled joint length, stress concentration, and crack propagation paths is analyzed to reveal the damage evolution process at the joint tips. The patterns of energy accumulation, release, and dissipation during loading are also examined to clarify how filled-joint length influences the energy storage limit of the rock mass and the risk of sudden failure.

A combined methodology of laboratory conventional triaxial compression tests and PFC3D particle-flow numerical simulations is employed to systematically investigate the influence of filled-joint length and inclination angle on the mechanical properties of limestone. Limestone specimens containing filled joints of varying lengths and inclination angles are prepared, and a series of triaxial compression tests are conducted to obtain their macroscopic mechanical responses, failure modes, and crack evolution patterns. Based on the experimental results, mesoscopic parameters are calibrated to construct the corresponding PFC3D numerical models, and simulations under identical conditions are performed to reveal, from a mesoscopic perspective, the mechanisms of force chain evolution, crack initiation and propagation, and energy transformation. Mutual verification and complementary analysis of the physical test and numerical simulation results elucidate the controlling effect of defect geometric characteristics on the strength, deformation, and failure of limestone.

Laboratory experiments and numerical simulations indicate that the failure mode of limestone is jointly governed by joint length and inclination angle. With increasing joint length, the peak strength and elastic modulus of the specimens generally decrease, indicating a substantial degradation in the load-bearing capacity and deformation resistance of the rock mass as the defect scale expands. During deformation, pronounced displacement concentration zones tend to form around the joints, accompanied by nonuniform stress distribution. Microcracks preferentially initiate at the joint tips and propagate along the joint orientation, causing rock deformation to shift gradually from globally coordinated behavior to localized concentration. The resulting damage evolution paths are strongly influenced by the spatial morphology of the joints. As joint extension increases, the influence range of the DFN III displacement field gradually diminishes, indicating a continuous reduction in the integrity and continuity of the rock mass structure, while the controlling effect of structural planes on rock deformation and failure becomes considerably more pronounced. Concurrently, energy dissipation in the initial stage is enhanced, whereas the capacity for elastic energy storage is reduced, and the balance of energy accumulation, release, and dissipation within the rock mass system is progressively disrupted.

A comprehensive analysis of the influence of filled joints on limestone is conducted from both macroscopic and mesoscopic perspectives, revealing the coupled controlling effects of joint geometric parameters on the mechanical properties of limestone. On this basis, a quantitative response expression describing the deterioration of limestone strength and deformation modulus with variations in joint geometric parameters is established, providing a reliable quantitative basis for evaluating the mechanical behavior of limestone with filled joints. Furthermore, from the mesoscopic perspectives of acoustic emission and crack evolution, the failure mechanism and damage evolution process of limestone with filled joints are systematically analyzed, clarifying the internal correlation between microcrack initiation and propagation and the macroscopic mechanical response. Overall, the findings deepen the understanding of the interaction mechanism between filled joints and limestone and provide theoretical support and practical reference for engineering stability analysis.