The physics of water imbibition into initially unsaturated sandstone is critical to the understanding of displacement processes and fluid transport in the vadose zone. The distribution of water within rock is important due to its significant influence on rock mechanical behavior. Here, therefore, we used nuclear magnetic resonance (NMR) technology to visualize and quantify the dynamics of water infiltration and distribution in initially unsaturated sandstone. The progression of water imbibition in sandstone specimens under the following two conditions were analyzed: (1) specimens soaked in water for different durations and (2) specimens soaked in water for the same duration and then held in this state for different durations. An analytic function was developed to estimate the sandstone moisture profile and to determine the unsaturated flow within the sandstone when the water distribution matched laboratory observations. Finally, a three-dimensional discrete element grain-based model was formulated that incorporates the local parallel-plate method, the unsaturated flow function, and the generalized effective stress principle. We used this model to effectively reproduce the process of water imbibition in the laboratory sandstone specimens. The effect of water imbibition on the mechanical properties of the studied sandstone was also evaluated. These results show that the strength of the core of the sample was reduced as water migrated from its surface to its center, resulting in a decrease in bulk sample strength as standing duration (i.e. water distribution uniformity) increased. The results of this study aid in our understanding of the influence of water imbibition on the mechanical behavior of sandstone, which is important for rock slope stability assessments following rainfall.

将水吸收到最初的非饱和砂岩中的物理过程对于了解渗流区中的驱替过程和流体运移至关重要。岩石中水的分布很重要，因为它对岩石力学行为的影响很大。因此，在这里，我们使用核磁共振（NMR）技术来可视化和量化初始不饱和砂岩中水的渗透和分布动力学。分析了以下两个条件下砂岩标本的吸水进程：（1）标本在水中浸泡了不同的时间，（2）标本在水中浸泡了相同的时间，然后在此状态下保持了不同的时间。当水分布与实验室观测值相匹配时，开发了一种解析函数来估算砂岩的水分分布并确定砂岩内部的非饱和流。最后，结合局部平行板法，非饱和渗流函数和广义有效应力原理，建立了三维离散元晶粒基模型。我们使用此模型有效地再现了实验室砂岩标本中的吸水过程。还评估了吸水对研究砂岩力学性能的影响。这些结果表明，随着水从其表面迁移到中心，样品核心的强度降低，导致整体样品强度随停留时间的延长而降低（即 水分配均匀性）提高。这项研究的结果有助于我们了解吸水对砂岩力学行为的影响，这对于降雨后岩石边坡稳定性评估很重要。