The conventional crumb test (CCT) is a simple and rapid test, originally used for assessing the dispersive tendency of clayey soils through visual observation of a small-scale soil specimen placed in a large volume of water. In this study, the disaggregation process occurring in soil in contact with water was followed in place of the soil dispersion in CCT. In order to describe quantitatively the process, an automated crumb test (ACT) was developed. The test method is based on temporal evolution of the soil specimen geometry during its disaggregation due to water infiltration. A series of tests were conducted on clay-sand mixtures with different initial water and clay contents, in order to show the potential of ACT. Image analysis applied on collected data with two digital cameras, revealed a general behaviour divided into a swelling step followed by a slump step starting as soon as the particles detach. By using temporal and geometric parameters, ACT revealed the ability of soils to absorb more or less water during the swelling step and then to disaggregate/crumble more or less rapidly. Finally, a correlation between the quantitative parameters from ACT and erosion characteristics from hole erosion test (HET) was attempted and discussed.