Method A
The seating pressure (at least 1 kPa) is applied to the clay specimen. After the initial deformations at the seating pressure are complete, the specimen is inundated with water in the oedometer cell and is allowed to swell vertically. The time-swell curve typically consists of three regions. An initial swell region, primary swell region, and secondary swell region (Figure 2.1). The minor initial swell is attributed to swelling of the macrostructure, while the major primary swell and minor secondary swell is attributed to microstructural swelling (Rao et al., 2006). The specimen is stepwise loaded after primary swell is complete using a load increment ratio of unity. The loading process is continued till the swollen specimen regains its initial void ratio/height. The external pressure needed to regain the initial void ratio e0, defines the swell pressure of the specimen (Figure 2.2).
The swell potential at the seating pressure relative to the initial void ratio e0 is given as:
(2.1)
where ese is void ratio after stabilized swell at seating pressure and e0 is the initial void ratio of the soil specimen at the seating pressure. This test method measures (a) the percent heave of the specimen at the seating pressure and (b) the swell pressure of the specimen (Figure 2.2).