EFFECT OF MATRIC SUCTION ON STRENGTH CHARACTERISTICS OF UNDISTURBED UNSATURATED SILTY CLAY

To study the influence of matric suction on the strength characteristics of soil, consolidated and drained triaxial shear tests on undisturbed silty clay were conducted using GDS unsaturated soil triaxial apparatus under different matric suction conditions. The results show that the peak strength of soil increases with the increase of matric suction, and the rate of increase increases first and then decreases. With increased matric suction, the total cohesion increases and the extent of this increase gradually decreases, while the effective internal friction angle decreases slightly and then tends to be stable. The effect of matric suction on shear strength is mainly reflected in the total cohesion. Matric suction has the most significant influence on soil strength at 50 kPa to 100 kPa. In the presence of matric suction, the area of action of water film on soil particles determines the change of total cohesion, and the pore air pressure and pore water determine the change in effective internal friction angle. The angle used to describe the increase in the shear strength of soil with an increase in matric suction is phi(b) = 28.2 degrees. According to Fredlund's strength theory, the formula of shear strength parameters of unsaturated silty clay in the study area under consolidation and drainage conditions was given, and the relationship between strength parameters and matric suction was fitted.