Desaturation is a new method to improve the liquefaction resistance of foundation by decreasing the saturation degree of saturated sand. Based on the coupling simulation method of water-gas two-phase flow reaction and soil skeleton deformation

a two dimensional numerical model is established to simulate the static liquefaction behavior under monotonic loading conditions. Also numerical simulation of undrained triaxial tests are carried out. By comparing the numerical results with the laboratory test results

it is found that the two-phase flow model shows great accuracy in describing the stress-strain relationship

stress path and pore water pressure growth in the static liquefaction process

which verifies the effectiveness of the two-phase flow simulation method. In addition

the saturation degree of desaturated loose sand during loading process increases until a stable value is reached. While the confining pressure is constant

the saturation degree at the end of loading linearly increases with the initial saturation. At the same time

the air in the sand is compressed under loading

which enables the desaturated sand to develop shear shrinkage with undrained condition. When the initial saturation degree of loose sand is reduced from 100% to 94.5%

pore water pressure coefficient B will decrease by 80%

the greatest pore pressure will decrease by 40%-50%

the undrained shear strength will increase by 2.0-2.5 times

and the residual strength can improve by more than 10 times. Therefore

this is the main mechanism of desaturation method to improve the liquefaction resistance

and the matric suction isn’t the main reason for desaturation method to improve the sand shear strength.