Quasi-saturated clay is assumed to consist of saturated matrix (soil skeleton and water) and occluded gas. Plastic volumetric strain of saturated matrix and gas is used as hardening parameter to reflect the plastic hardening behavior of quasi-saturated clay. The variation of gas solubility coefficient with temperature and salinity in water and the variation of pre-consolidation stress with occluded gas are used as key factors. Based on the theory of critical state mechanics

an elastoplastic model is proposed to reflect the influence of the pressure change of the occluded gas on the mechanical characteristics of quasi-saturated clay. There are 10 material parameters in the proposed model

all of which can be obtained from compression test and triaxial shear test. By comparing against existing experimental data

the results show that the model can well simulate the stress-strain relationship

pore water pressure development and saturation evolution under undrained stress path. The proposed elastoplastic model is simple in form and its parameters can be easily determined

and it provides an important theoretical basis for the design

calculation and disaster control of geotechnical engineering problems in quasi-saturated clay foundations.