The influence of sand pore structure on air migration during air injected desaturation process

Air injection desaturation method is a kind of liquefaction mitigation measure to reduce the saturation degree of soil by engineering measures to inject air into the interior of liquefiable soil. In order to study the air transport patterns and gas phase saturation in saturated sand, the visual sheet model test of saturated sand air-injection was carried out. The results show that:(1) According to the characteristics of the morphology of the transport path of the injected air and the time-range change of the air pressure during the air injection process, the air injection process is divided into four stages: Ⅰ breakthrough stage, Ⅱ expansion stage, Ⅲ re-expansion stage, and Ⅳ stabilized overflow stage. The flow state of the gas is controlled by the size of the pore throat and the connectivity of the pore structure and the air injection process shows two typical morphological features: channel flow dominated by inertial forces and chamber flow dominated by viscous and capillary forces. (2) The minimum air injection pressure Pmin in stage I is equal to the sum of hydrostatic pressure u and capillary resistance Pcr. Pcr is negatively correlated with the characteristic particle size deff and positively correlated by Dr. (3) Sr,a in the coarse sand group shows a positive correlation with deff and a negative correlation with Dr. Its desaturation value changes significantly in both II and III stages. In the medium and fine sand groups, Sr,a is negatively correlated with deff and positively correlated with Dr. Their desaturation values are basically concentrated only in stage II. (4) The process of achieving desaturation in the coarse sand group relies mainly on easily expandable connectivity channels, whereas the medium-fine and fine sand groups rely mainly on the accumulation of gases in the region of low flow resistance on the way to the selected flow path.