Air-coupled effects on triaxial behavior of silty specimens under a constant confining pressure and various exhausted conditions

抄録

Many studies in unsaturated soil mechanics have focused attention on suction difference. It is also necessary to take into account the flow and high compressibility of the pore air. During rainfall, earthquakes, or other conditions under which air cannot be sufficiently exhausted, changes occur in the pore air pressure, causing changes in the pore air volume. There is an increasing need for methods of testing and analysis capable of dealing with cases where the pore air pressure varies from atmospheric pressure. Based on the background, numerical simulation of unsaturated silty triaxial tests under undrained and unexhausted conditions and under undrained at various controlled air pressure levels was carried out using a soil-water-air coupled analysis code taking the triaxial test as an initial value/boundary value problem. The processes of back pressure increase, suction variation, consolidation, and shear were simulated beginning from a “single initial condition” as in the case of the experiments. As a result, in the simulations of the undrained and unexhausted shear tests, it was shown that since the mechanical behavior is significantly affected by the compressibility of air, it is possible, by simply taking into consideration air coupling, to describe the differences in the mechanical behavior corresponding to the differences in the degree of saturation. Through the simulations of the undrained shear tests with air pressure control, it was found to be possible to reproduce soil mechanical behaviors that change from hardening to softening corresponding to the level of volumetric constraint. Softening behavior can be portrayed on the basis of the loss of structure described by the SYS Cam-clay model. In addition, behaviors that could not be explained without the effects of factors other than air coupling such as suction were also shown.