Gas Effect in Constitutive Modeling of Unsaturated Soils

the existence of gas in unsaturated soils make the properties of unsaturated soils much more complicated than saturated soils. It may change the permeability and affect groundwater recharge, remediation of contaminated soils, irrigation, the instability of soil structure, and so on. The paper explained the gas patterns divided by different researchers and pointed that in either the gas internally continuous situation or the gas completely sealed situation with large gas bubbles, the gas phase will not connect with the outward atmosphere and its pressure will of course change during soil deformation. The coupled deformation of gas phase and the other two phases is elaborated. According the work input of unsaturated soils, it is necessary to take gas pressure as a third stress variable to describe the soil behaviour together with the generalized effective stress and matric suction. By introducing a variable which could represent the plastic gas deformation into soil hardening equation, the gas effect can then be reflected in the constitutive equation of unsaturated soils.