Sufficient experimental evidence shows that a soil cannot reach the fully saturated condition during wetting process

even the matric suction decreases to 0 kPa

and small amount of air is trapped in the pores

rendering the soil to be more compressible than expected in the early beginning of compression process. At this state

the behavior of the soil is different from that of its saturated counterpart. On the other hand

existing coupling constitutive models of unsaturated soils would predict that the soil becomes fully saturated

which is inconsistent with experimental results. Considering the air entrapment effect

a constitutive model with coupling capillary hysteresis and plastic deformation is modified. Comparison of the simulated results and experimental data illustrates that the new model can effectively address the effect of air entrapment on the behavior of unsaturated soils.