Based on the principle of thermodynamics and the 2D computational model of liquid bridge

the relationship between matric suction and volumetric water content is derived with three unequal diameters of soil particles. The influences of particle size

gradation and the contact angle of soil particles on the soil-water characteristic curve are studied by simplifying soil particles as the constrained particle size

median particle size and effective particle size. The computational results show that the larger the size of the soil particles has the smaller corresponding matric suction under the same volumetric water content. Under the same matric suction

the volumetric water content of the soil particles is lower when the coefficient of non-uniformity ( ) is larger or the soil particle is more uneven. The smaller the contact angle is

the better the hydrophilic property of the soil particles is. The volumetric water content under the same matric suction is also greater when the contact angle is smaller. The air-enter value of the soil-water characteristic curve decreases with the decrease of the contact angle.