The mechanical behavior of rock under cyclic loading is quite complicated compared to monotonic loading or unloading conditions. The triaxial cyclic loading and unloading testing of rock specimens under 6 confining pressures (σ3) was carried out through the MTS 815 rock mechanics testing system, to explore the strength, deformation, and expansion characteristics of the rock specimens. The stress–strain curves of the rock specimens in the triaxial cyclic loading and unloading testing presented the hysteresis effect. Besides, as σ3 increased, the rock specimen strength increased, while the failure form brittle to ductile. The elasticity modulus (El) increased first and consequently decreased as the cycle index increased, while it increased as σ3 increased. However, the generalized Poisson’s ratio (μl) increased as the cycle index increased, whereas it decreased as the σ3 increased. Based on the Mohr–Coulomb strength criterion and plastic shear strain (γp) as the plastic parameter, the subsequent yield plane model of the loaded rock was characterized by generalized cohesion (c´) and generalized internal friction angle (φ´). Ultimately, the evolution rules of c´, φ´ and Ψ (dilatancy angle), with σ3 and γp were revealed. Moreover, the post-peak dilatancy angle models with regard to the influence of σ3 and γp on the volume dilatancy of the rock specimen were established, which indicated that Ψ increased first and consequently decreased along with the γp increase, whereas it decreased as the σ3 increased.

中文翻译：

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三轴循环加卸载条件下岩石强度及变形特性试验研究

与单调加载或卸载条件相比，循环加载下岩石的力学行为非常复杂。通过MTS 815岩石力学测试系统对岩石试样在6个围压(σ3)下进行三轴循环加卸载试验，探索岩石试样的强度、变形和膨胀特性。三轴循环加载和卸载试验中岩石试样的应力-应变曲线呈现滞后效应。此外，随着σ3的增加，岩石试件强度增加，破坏由脆变韧。弹性模量（El）随着循环指数的增加先增加后减小，而随着σ3的增加而增加。然而，广义泊松比（μl）随着循环指数的增加而增加，而随着 σ3 的增加而减少。基于Mohr-Coulomb强度准则和塑性剪切应变（γp）作为塑性参数，加载岩石的后续屈服面模型具有广义内聚力（c´）和广义内摩擦角（φ´）特征。最终，揭示了 c´、φ´ 和 Ψ（剪胀角）以及 σ3 和 γp 的演化规律。此外，建立了关于σ3和γp对岩石试样体积剪胀影响的峰后剪胀角模型，表明Ψ随着γp的增加先增加后减小，而随着σ3的增加而减小。增加。随后加载岩石的屈服平面模型以广义内聚力 (c´) 和广义内摩擦角 (φ´) 为特征。最终，揭示了 c´、φ´ 和 Ψ（剪胀角）以及 σ3 和 γp 的演化规律。此外，建立了关于σ3和γp对岩石试样体积剪胀影响的峰后剪胀角模型，表明Ψ随着γp的增加先增加后减小，而随着σ3的增加而减小。增加。随后加载岩石的屈服平面模型以广义内聚力 (c´) 和广义内摩擦角 (φ´) 为特征。最终，揭示了 c´、φ´ 和 Ψ（剪胀角）以及 σ3 和 γp 的演化规律。此外，建立了关于σ3和γp对岩石试样体积剪胀影响的峰后剪胀角模型，表明Ψ随着γp的增加先增加后减小，而随着σ3的增加而减小。增加。