Effect of Air Compression and Counterflow on Shallow Landslides Under Intense Rainfall

Under heavy rainfall, the surface soil is saturated quickly. Rainwater percolates down as a wetting front, displacing air in soil. Rainwater infiltration into the unsaturated zone is potentially affected by air compression ahead of the wetting front. For a large and shallow slope area, air compression ahead of the wetting front will lead to a fluctuant air pressure in excess of atmospheric pressure. In this study, the process of air compression and counterflow ahead of wetting front was simply analyzed. An extended Green Ampt model is introduced considering air compression and counterflow. Based on the model, the infiltration of a shallow slope subjected to an intense rainfall was studied. The limit equilibrium method and the Mohr-Coulomb failure criterion were readily applied to calculate the safety factor of slope. Considering the effects of the air pressure fluctuation produced by air compression and counterflow ahead of the wetting front, a stability analysis model was presented, which can be readily used for estimating the likelihood of a shallow landslide triggered by intense rainfall. It is found that the gauge air pressure ahead of the wetting front, on the one hand, leads to the formation of static water pressure that serves to reduce the normal stress of the interface at wetting front in saturated zone, hence has an adverse effect on the stability of slope, on the other hand, delayed the downward movement of the wetting front, accordingly, decrease the likelihood of landslide.