Experimental infiltration of unsaturated loess under air action and simulations of a water-air two-phase flow model on slopes

Loess, which is
widely distributed in China, forms unique geographical areas prone to frequent
geological disasters. The thick vadose zone in these regions is characterized
by the coexistence of solid, liquid, and gas phases, significantly complicating
water infiltration processes. The influence of soil air pressure must be
considered when modeling water infiltration in such areas, rather than relying
solely on single-phase flow models.

In this study,
water and air migration mechanisms are investigated under open and closed
conditions through laboratory experiments and numerical simulations. After
simulating scenarios such as precipitation and irrigation, a comparative
analysis revealed the effects of air–water two-phase flow versus single-phase
flow. The results demonstrate that under closed conditions, the pore air
pressure increases substantially, retarding water infiltration. Air pressure
fluctuations cause variations in the infiltration velocity of the wetting
front. Moreover, the presence of gas connects the water above and below the
wetting front, causing the water flux beneath the wetting front to fluctuate in
response to air pressure changes. Minor air pressure changes due to precipitation
have negligible impacts, whereas irrigation-induced air pressure variations
significantly affect water infiltration and slope stability.<br>