an engineering geological characterisation of tropical clays - GBV

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7.4.7 Swelling pressure and percentage swelling
Black clays have been shown to exhibit considerable swelling capability, i.e. free swell of
between 100 and 200% when allowed free access to water from a dry state. On the other hand,
red soils exhibit a limited swelling capability when saturated with water (free swell= 15-
20%); and as a result, no swelling pressure determination was performed on these soils.
7.4.7.1 Swelling pressure test
Swelling pressure, SP, of clays is the pressure required to prevent swelling by constraining the
clays to maintain constant volume when saturated with water (Nelson and Miller, 1992).
Swelling pressures of over 1 MN/m² have been registered for some heavily overconsolidated
clays (Head, 1988). In this study, swelling pressures of 49-104 kPa have been determined for
the black clays.
Swelling pressure determination was carried out according to a method devised by Head
(1988), and employed the British Standard oedometer consolidation cell as described in a
previous section (Plate 7.9).
Plate 7.9. Swelling pressure determination of clay soils.