Constitutive modelling of overconsolidated gassy clay

Fine-grained soils with free gas bubbles can be frequently encountered in the seabed or lakebed. Gassy soils can become overconsolidated due to sediment movement or submarine landslides. The presence of free gas bubbles in fine-grained soils can cause large-scale submarine landslides and offshore foundation failures. The gas bubbles can have either beneficial or detrimental effect on the soil strength and stiffness, depending on the stress state and gas volume fraction. A constitutive model accounting for the effect of overconsolidation on dilatancy is presented. The soil is considered as a composite with saturated soil matrix and cavities. The gas cavities are assumed to have a detrimental effect on the plastic modulus and shear strength. Bubble flooding makes the saturated soil matrix partially drained under a globally undrained condition, which has a beneficial effect on the soil stiffness and undrained shear strength. A series of undrained triaxial compression tests have been carried out on gassy Malaysian Kaolin and the data has been used to validate the model. The model can be used for assessing the slope stability and bearing capacity of foundations in gassy clay.