A Nonlinear Creep Damage Model of Layered Rock under Unloading Condition

Wang Ruihong; Jiang Yuzhou; Yang Chao; Huang Fei; Wang Yuxuan

摘要

Triaxial unloading creep tests of layered rock specimen of Jinping II hydropower station were carried out using the rock creep testing machine; thus the creep deformation curves under different confining pressures were acquired. The test results showed that, in addition to the obvious unloading creep characteristics of rock specimen, the nonlinear accelerating creep deformation emerged under the last stage confining stress condition, and the whole creep curves presented the typical rock creep three stages. On the other hand, the Burgers creep model constitutive equations under the three-dimensional stress state were also deduced. Based on the creep test data, through identifying the creep parameters using the optimized algorithm, the corresponding parameters of triaxial creep constitutive model were obtained. By comparative analysis of creep parameters, it can be concluded that creep parameters nonlinearly degraded with the decrease of confining pressure gradually. Moreover, when the load is below the long-term strength of rock, the creep parameters are only related to the unloading ratio, while in the case that the load is larger than the long-term strength of rock, the unloading creep parameters are related to both unloading ratio and creep time. According to the creep parameters under the first-stage stress level, and through introducing unloading ratio damage factor to describe the degrading rule of creep parameters on other stress levels, the method of uniformity determining the creep parameters was proposed. It was assumed that the damage degree in rock interior was relative to both unloading ratio and creep time; a nonlinear creep damage model of rock under unloading was proposed, which could better reflect the nonlinear characteristics of rock creep. The results showed that rock nonlinear creep damage model achieved perfectly consistent results with the creep test.

机译：采用岩石蠕变试验机进行了金平II水电站层状岩石标本的三轴卸载蠕变试验;因此，获得了不同狭窄压力下的蠕变变形曲线。测试结果表明，除了岩石标本的明显卸载蠕变特性外，在最后一级限制应力条件下出现的非线性加速蠕变变形，整个蠕变曲线呈现典型的岩石蠕变三个阶段。另一方面，还推导出三维应力状态下的汉堡蠕变模型结构型方程。基于蠕变测试数据，通过使用优化算法识别蠕变参数，获得了三轴蠕变本构模型的相应参数。通过对蠕变参数的比较分析，可以得出结论，蠕变参数随着限制压力的降低而非线性地降低。此外，当负载低于岩石的长期强度时，蠕变参数仅与卸载比有关，而在负载大于岩石的长期强度的情况下，卸载蠕变参数是相关的卸载比率和蠕变时间。根据第一阶段应力水平下的蠕变参数，并通过引入卸载比损伤因子来描述其他应力水平的蠕变参数的降低规则，提出了确定蠕变参数的均匀性方法。假设岩石内部的损伤程度相对于卸载比和蠕变时间;提出了卸载下岩石的非线性蠕变损伤模型，这可以更好地反映岩石蠕变的非线性特征。结果表明，岩石非线性蠕变损伤模型与蠕变试验完全一致的结果。

A Nonlinear Creep Damage Model of Layered Rock under Unloading Condition

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