CONTRIBUTION OF MATRIC SUCTION TO SHEAR STRENGTH OF UNSATURATED REMOULDED LOESS SOILS

Shear strength of unsaturated soil increases as its matric suction increases and the degree of saturation decreases.However,effect of matric suction to shear strength can be greatly different for different types of unsaturated soils.In this paper,the relationship between matric suction and shear strength of the unsaturated remoulded loess soil is examined with experimental approach.It is found that as matric suction increases,the soil shear strength varies nonlinearly.The variation has clear four stages: increasing,decreasing and keeping relatively constant.Particularly,the four stages can be identified based on the correlations between matric suction and shear strength,consistent with those shown on the soilwater characteristic curve.Matric suction of 5 kPa, 60 kPa, 170 kPa are critical values for the four stages.Notably,shear strength of the soils attain their peak values at matric suction of 60 kPa.Variation of apparent cohesions of the soils with matric suction shows the same trend as those of shear strengths,whereas variation of apparent internal friction angles of the soils increases stage by stage.It is also found that shear strength parameter b of the unsaturated loess soil is not a constant.