Expansive soils are one of the problematic soils in the world. The volume change of this soil is depended on its moisture content. A new method to characterize this type of soil is determined from the results of oedometer tests, carried out on expansive and non-expansive soils. The ratio between the compression index (Cc) and the swelling index (Cs) is defined. A threshold swelling pressure (σs) value and zones delimited by a Cc/Cs value are identified to distinguish expansive from non-expansive soil specimens. And for a Cc/Cs >15, the swelling pressure is almost equal to zero.


Expansive soils are found in arid or semi-arid areas. This type of soil often causes serious damage to buildings, especially lightweight buildings. It generally consists of clays, predominantly of the smectite group. With regard to the damage caused by swelling soil, the study of the behaviour of foundations on this type of soil is a topic of great interest, especially for many African countries (Kalantari 2012; Nelson et al. 2015).

Many researchers have been interested in the phenomenon of swelling, to understand how it can occur and to find which methods are appropriate to measure the swelling pressure and to mitigate the swelling phenomenon (Sridharan & Prakash 2016; Aniculaesi & Lungu 2019, Bouassida et al. 2022).

The volume of expansive soils changes depending on its water content. The process of soil swelling occurs gradually and is influenced by the saturation of the soil and also by the clay structure of the soil (Medjnoun et al. 2014). During this process, the clay particles are pushed apart due to the water molecules and other cations carried by the water, leading to an increase in swelling pressure (Elarabi 2010). In general, a soil has a shrink – swell behaviour because it contains a group of clays called smectite group, in particular montmorillonite (Chen 1988).

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