1. Shear Strength of Soil τ f = c + σ ’ tan φ τ f = shear strength c = cohesion φ = angle of internal friction σ 1 σ 1 major principle stress σ 3 σ 3 Minor principle stress Confining stress σ n τ f

2. Shear Strength of Soil σ 1 Shear stress σ 3 σ 3 Normal stress σ n Consider the following situation: A normal stress is applied vertically and held constant A shear stress is then applied until failure

5. c φ Shear stress normal stress Plotting 2 or more points provides the following Direct Shear Test

8. c = 0 φ Shear stress normal stress Typical plot for sands - Drained Condition Direct Shear Test

9. Direct Shear Test φ Shear stress normal stress Typical plot for clays - drained condition Overconsolidated OCR >1 normallyconsolidated OCR=1 c

11. Triaxial Shear Test

17. Shear Strength of Soil c Shear stress normal stress Typical UU plot for clays