Capillary Water in 2-D Drying-Cracking Sub-Grain Scale Soil Models: Dynamics and Instabilities of Haines Jumps

Changes in capillary water morphology in a cluster of three wet long cylindrical grains as reported in Mielniczuk and Hueckel (2022, ) affect capillary forces evolving during drying. The paper focuses on a stable motion of menisci (air/liquid interfaces) and their unstable (Haines) jumps. The meniscus instabilities were shown in the past to be a trigger of soil drying-cracking. The forces considered are Laplace pressure and surface tension resultants deduced from the menisci imaged every 10 s. The Laplace pressure for cylindrical clusters depends on a single curvature of the meniscus. Several known criteria the capillary body instability are examined using the experimental data. An extended Gibbs criterion points to a source of the instability. The instability is lost when the meniscus approaches the throat between the grains and when the balance is lost between the changes of forces of the Laplace pressure and of the surface tension acting at the meniscus. The presence of the surface tension forces in the instability considerations in addition to the Laplace pressure distinguishes Gibbs criterion from other criteria. Gibbs meniscus energy estimate also provides an inertia force arising to maintain the linear momentum balance for the meniscus, and a duration of the jump.