Shear Strength of Soils

Shear strength is defined as the maximum shear stress that the soil may sustain without experiencing failure. Shear strength is a critical parameter in geotechnical projects. It is needed to derive the bearing capacity, design retaining walls, evaluate the stability of slopes and embankments, etc.

According to the Mohr-Coulomb failure criterion (equation 1), the shear strength of soils consists of two components, cohesion (c) and frictional angle (φ) and is also dependent on the normal effective stress (σ').

τ=c+σ’tanφ                                                                     (1)

Strength parameters (cohesion and friction angle) are derived both from in situ and laboratory testing.

The most common in-situ tests are the following:

• Vane Shear Test.
• Standard Penetration Test (SPT)
• Cone Penetrometer Test (CPT)
• Pressuremeter

The most common laboratory tests are the following:

• Direct Shear Test
• Unconfined Compression (UCC) Test
• Simple Shear Test
• Triaxial Compression Test