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• A plastic Stillinger-Weber potential for soft rocks is proposed. • The plastic fracture behavior of soft rocks is effectively simulated. • The dependence of simulation results on mesh size is effectively mitigated. • Influence factors on the failure behaviors of soft rock tunnels are investigated. Soft rocks present some undesirable behaviors, such as low strength, high plasticity and softening. These traits pose challenges in the design and construction of soft rock tunnels. To address these issues and model plastic fracture behaviors of soft rocks, we proposed a plastic Stillinger-Weber (PSW) potential and integrated it into the discretized virtual internal bond (DVIB) model. The PSW-DVIB model combines the strengths of the plastic DVIB and the SW-DVIB models. It not only effectively reproduces the plastic fracture behavior but also accurately reflects the Poisson's ratio. Moreover, due to the inclusion of fracture energy in the PSW potential, the simulation results are basically mesh size independent. The PSW-DVIB model is then utilized to investigate the failure behaviors of soft rock tunnels. The effects of the coefficient of lateral pressure, in-situ stress, Poisson's ratio and tunnel shape on tunnel failure are investigated. The simulated results indicate that the coefficient of lateral pressure has significant influence on the failure zone distribution of the surrounding rock. With the coefficient of lateral pressure increasing, the failure degree of surrounding rock decreases firstly and then increases. The optimum coefficients of lateral pressure for the stability of circular, arched and square tunnels are about 1.00, 0.75 and 0.75, respectively. When the in-situ stress or Poisson's ratio is larger, the influence of the coefficient of lateral pressure on tunnel failure is more obvious. The influence of the coefficient of lateral pressure on square tunnels are more significant than the arched tunnels, and then the circular tunnels. These findings provide valuable insights for the design and construction of soft rock tunnels. [ABSTRACT FROM AUTHOR]

• The dynamic fracturing behaviors of fissured rock under unloading condition are studied. • The tensile-shear transition of fracture pattern is found when increasing the initial stress level. • The unloading failure of rock with parallel and randomized multiple flaws are analyzed; • The findings can improve the understanding on rock burst. Unloading can cause many geotechnical disasters, e.g., the rock burst. The underlying mechanism of rock failure is the propagation and coalescence of cracks. To get insight into rock unloading failure, the discretized virtual internal bond (DVIB) model in conjunction with element partition method (EPM) is used to simulate the dynamic fracturing process under unloading conditions. At first, the samples with the single flaw are simulated under unloading conditions. It is found that the fracturing pattern exhibits the tensile-shear transition with the initial stress level increasing. When the flaw inclination is closer to 45 degree or the flaw is longer, shear cracks are more likely to occur. Then, the unloading failure process of rock with multiple flaws are simulated. It is found that the inclination of the parallel flaws has remarkable influence on the unloading failure of rock. When the inclination angle is about 45 degree, the rock is easier to fail. For the rock with multiple randomized flaws, the amount of flaws has slight influence on acoustic emission counts. However, the configuration of randomized flaws can significantly affect the fracture process and failure patterns. These findings can improve understanding of rock burst and provide valuable references for the prediction of unloading failure of rock. [ABSTRACT FROM AUTHOR]

• A trilinear damage potential is developed to simulate quasi-brittle fracture simulation. • Both the pre-peak and post-peak damage are captured in this potential. • The mesh size sensitivity is significantly relieved due to the fracture energy conservation. To more accurately simulate the fracture propagation in a quasi-brittle material, a trilinear damage potential is developed, which accounts for both the damage and fracture energy. The bond potential is divided into three stages, namely the linear elastic, the pre-peak damage and the post-peak damage stage. Once the bond enters the damage stage, it can be completely unloaded without any residual irreversible deformation. This potential is embedded into the discretized virtual internal bond (DVIB) model to simulate the failure process of quasi-brittle material. The simulation examples suggest that it can capture the damage behavior of material in both the pre-peak and the post-peak stage. The mesh size sensitivity can be significantly relieved due to the embedded fracture energy in the bond potential. How significant the micro bond parameter plays a role is size-dependent. The simulation results suggest that the DVIB with this potential can well simulate the fracturing process of brittle material. It provides an effective lattice method to simulate the failure process of a quasi-brittle material with consideration of damage. [ABSTRACT FROM AUTHOR]