Theoretical soil—water characteristic curve for unsaturated soils

Based on thermodynamics, nonlinear formulas were established and numerically programmed with an iterative approach for defining equation of meniscus between two regular ball-type soil particles with equal diameter. Therefore the matric suction could be determined accordingly. Considering effective action area of matric suction on granular media, the concepts of equivalent matric suction and generalized soil—water characteristic curve were presented. It was shown that equivalent matric suction depended on saturation and it started from zero for zero saturation and would gain its peak value for a certain saturation where the soil would mobilize its maximum strength and then weakened. The computations and discussions were made for the loosest assembling pattern of soil particles with equal diameter. It was demonstrated that both matric suction and equivalent matric suction would rapidly reduce with the increase of spacing of particles and the soil—water characteristic curves respectively based on both concepts were highly associated with the variation of contact angle of particles.