The characteristics of static and dynamic strength of unsaturated loess are studied by triaxial compression test and dynamic torsional shear test

and the formulas for calculating effective stress of unsaturated loess and the method of Mohr-Coulomb strength index calculation in dynamic torsional shear test are also discussed. Simplified formulas for the effective stress calculation of unsaturated loess unsaturated loess are proposed. The rules that static strength of intact loess and man-made loess change with water content and density and dynamic strength changes with water content and vibration number are also analyzed. The relativity of strength index between static and dynamic test of loess is analyzed. The static strength index approach to the dynamic strength index at vibration number 20. The correlation of strength index between static and dynamic test of unsaturated loess is remarkable

and some experience formulas of ascertaining dynamic strength index according to static strength index are presented.