Soil–water–air coupled finite deformation analysis based on a rate-type equation of motion incorporating the SYS Cam-clay model

With the aim of expanding the soil skeleton–water coupled finite deformation analysis code, mounted with the SYS Cam-clay model and capable of accommodating inertia forces to deal seamlessly with soils from the unsaturated to the saturated states, a new soil skeleton–water–air coupled finite deformation analysis method (u–pw–pa–sw formulation), based on the three-phase mixture theory, was proposed. The following are the main observations obtained through computations performed under simple conditions using this new method.(1)A simulation of constant cell pressure undrained (and unexhausted) triaxial tests on dense sand specimens with a degree of saturation of 99.9%, which in reality could be considered as “saturated soil,” was carried out. It was shown that when the back pressure was not sufficiently large, the existence of air caused desaturation to take place due to the effect of volumetric expansion and that no increase in deviator stress was observed. It was confirmed that the results of this simulation agreed with the experimental results.(2)Unlike the conventional method of analysis, in which the degree of saturation is not explicitly made an unknown, the current method of analysis, in which the degree of saturation is explicitly made an unknown (u–pw–pa–sw formulation), was shown to be capable of expressing the increase in the degree of saturation even in the case of insular air saturation when the suction was 0.