In the present paper, we investigate how water acts to weaken rock in two complementary ways: mechanically through the generalized effective stress principle, and chemically through time-dependent rock-fluid reactions that allow subcritical crack growth. These processes, together with capillary suction and stress corrosion, were incorporated into a three-dimensional discrete element grain-based model to investigate both the time-independent and the time-dependent mechanical behavior of partially saturated sandstone at the mesoscale. The capillary parameters related to capillary suction and subcritical parameters related to stress corrosion in the model were calibrated to match the deformation behavior of partially saturated sandstone observed in laboratory. Following this calibration, numerical simulations of partially saturated sandstone with different levels of saturation were performed in uniaxial compression. The simulations show that both the peak strength and elastic modulus of the sandstone decrease as a function of increasing saturation and that the relationships between these properties can be expressed by negative exponential functions. The simulations are in good agreement with the experimental results. Second, the long-term brittle deformation of partially saturated sandstone with different levels of saturation under a constant stress level was modeled. The results show that time-to-failure during brittle creep decreases, and the initial strain and the minimum creep strain rate increases, as a function of increasing saturation, as also observed in laboratory. The simulations also highlight the formation of tensile cracks as the main deformation mechanism during brittle creep. Finally, brittle creep in partially saturated sandstone samples with different levels of saturation was studied under different stress levels. These simulations show that the minimum creep strain rate and the time-to-failure as a function of stress can be well described by exponential relations. We conclude that the proposed model permits a deeper understanding of time-independent and time-dependent deformation and failure of partially saturated sandstone at the mesoscale.

在本文中，我们研究了水如何以两种互补的方式削弱岩石：通过广义有效应力原理进行机械作用，以及通过允许亚临界裂纹扩展的时间相关的岩石-流体反应进行化学作用。这些过程与毛细管吸力和应力腐蚀一起被纳入基于三维离散元颗粒的模型，以研究中尺度部分饱和砂岩的时间无关和时间相关的力学行为。对模型中与毛细管吸力相关的毛细管参数和与应力腐蚀相关的亚临界参数进行校准，以匹配变形行为实验室观察到的部分饱和砂岩。在此校准之后，在单轴压缩下对具有不同饱和度的部分饱和砂岩进行了数值模拟。模拟表明，砂岩的峰值强度和弹性模量都随着饱和度的增加而降低，并且这些特性之间的关系可以用负指数函数表示。模拟结果与实验结果非常吻合。其次，模拟了在恒定应力水平下具有不同饱和度的部分饱和砂岩的长期脆性变形。结果表明，脆性蠕变期间的破坏时间减少，初始应变和最小蠕变应变正如在实验室中观察到的那样，速率随着饱和度的增加而增加。模拟还强调了拉伸裂纹的形成是脆性蠕变过程中的主要变形机制。最后，研究了不同饱和度下部分饱和砂岩样品在不同应力水平下的脆性蠕变。这些模拟表明，最小蠕变应变率和作为应力函数的失效时间可以用指数关系很好地描述。我们得出的结论是，所提出的模型可以更深入地了解中尺度部分饱和砂岩的时间无关和时间相关变形和破坏。