Formation and evolution of water menisci in unsaturated granular media
Formation and evolution of water menisci in unsaturated granular media
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DOI：
10.1680/geot.11.p.034
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发表时间：
2012-03
期刊：
影响因子：
5.8
通讯作者：
S. Lourenço;D. Gallipoli;C. Augarde;D. Toll;P. Fisher;A. Congreve
中科院分区：
文献类型：
--
作者：
S. Lourenço;D. Gallipoli;C. Augarde;D. Toll;P. Fisher;A. Congreve
在潮湿的颗粒状材料中，如非饱和土壤，松散的颗粒通过作用于颗粒间接触处的毛细力结合在一起。这些毛细力的大小取决于表面张力和半月板的曲率半径，而半月板的曲率半径又取决于空气/水界面与固体颗粒表面的接触角。半月板通常被认为主要是凹在空气的一面与负水压（相对于大气）。这方面的证据来自毫米尺度的直接观测或理论假设。本文介绍了来自微米尺度颗粒的环境扫描电子显微镜的数据，这些数据与这一假设相矛盾，并首次表明，对于给定的含水量，空气/水界面和颗粒之间的接触角可以产生各种半月板形状，曲率并非都在空气的一侧凹下。研究发现，在具有不同粒径、形状和性质的理想和天然颗粒材料中，水半月板的曲率可以沿着单个半月板的边界变化，或者在微米尺度上从一点到另一点不同，并且还取决于材料的性质和润湿历史。半月板可以有主要的凸形状（对应于压缩毛细压力）和主要的凹形状（对应于拉伸毛细水压）。这些观察结果证实了空气/水界面（通常也被称为“可收缩皮肤”）表面张力在将颗粒聚集在一起方面的重要性。
Loose particles in moist granular materials, such as unsaturated soils, are held together by capillary forces acting at the interparticle contacts. The magnitude of these capillary forces depends on the surface tension and on the radius of curvature of the menisci, which in turn depends on the contact angle of the air/water interface against the surface of the solid particles. Menisci are usually assumed to be predominantly concave on the side of the air with negative water pressure (relative to the atmosphere). Evidence for this comes from direct observations at the millimetre scale or from theoretical assumptions. This note presents data from environmental scanning electron microscopy of particles at the micrometre scale that contradict this assumption and show for the first time that, for a given water content, the contact angle between air/water interfaces and grains can give rise to a variety of meniscus shapes, with curvatures not all concave on the side of air. It was found that the curvature of water menisci, in both idealised and natural granular materials with variable particle sizes, shapes and nature, could vary along the border of a single meniscus or differ from one point to another separated at the micrometre scale, and is also dependent on the nature of materials and wetting history. Menisci can have both predominantly convex shapes (corresponding to compressive capillary pressure) and predominantly concave shapes (corresponding to tensile capillary water pressure). These observations confirm the importance of surface tension in the air/water interfaces (often also referred to as ‘contractile skin') in holding particles together.