Groundwater-induced deformation of natural rock slopes is typically interpreted to be related to changes in pore pressure. Rock, however, is a porous medium that has been shown to expand on contact with water. Here, we present insights into surface deformation of free-standing 115 × 65 × 35 mm granite prisms with water continuously infiltrating from the upper surface over 16 – 24 hours under ambient laboratory environmental conditions. Digital image correlation analysis indicates a mean extensional strain due to wetting of approximately (4 – 4.7) × 10⁻⁴, equivalent to an internal pressure of 40 – 47 MPa, assuming linear-elastic material behaviour. Nanoscale adsorption theory indicates the contribution from adsorption of water onto free surfaces may be 18.4 MPa, while capillary condensation generates pressure up to 30.9 MPa. It is likely a majority of strains is the result of water entering micro pores with radius less than 5 nm, which account for 1.16% of the porosity. Our relatively simple experimental setup may serve as a useful tool for analyzing moisture-induced deformation in a range of geological materials.

地下水引起的天然岩石边坡变形通常被解释为与孔隙压力的变化有关。然而，岩石是一种多孔介质，已被证明与水接触时会膨胀。在这里，我们展示了在周围实验室环境条件下，在 16-24 小时内水从上表面连续渗透的独立式 115 × 65 × 35 毫米花岗岩棱柱的表面变形。数字图像相关分析表明由于润湿而产生的平均拉伸应变约为 (4 – 4.7) × 10 ^-4, 相当于 40 – 47 MPa 的内部压力，假设线性弹性材料行为。纳米级吸附理论表明，水吸附到自由表面的贡献可能为 18.4 MPa，而毛细冷凝产生的压力高达 30.9 MPa。很可能大部分应变是水进入半径小于 5 nm 的微孔的结果，占孔隙率的 1.16%。我们相对简单的实验装置可以作为分析一系列地质材料中水分引起的变形的有用工具。