Definition of Soil Shear strength

Tuesday, October 30, 2012 9:47
Posted in category Soil Mechanics 2
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Soil Shear strength

The soil shear strength is a measure of its resistance to deformation by continuous displacement of its individual soil particles.

Soil shear strength is an important consideration in foundation bearing capacity analysis, highway and airfield design. It is also very important in slope stability of earth embankments and retaining wall construction.

The soil shear strength is derived from three basic components.

  1. How much resistance does soil particles show against displacement because of interlocking of the individual soil particles.
  2. Resistance to particle translation because of friction between individual soil particles at their common points of contact.
  3. Cohesion between the surface of soil particles.

The above components are actually effective in resisting shear deformation. Which of these components, or combination of components is actually effective depends on

  1. Whether the soil is cohesive or not.
  2. The soil drainage and consolidation conditions before and during the shearing process.

 Cohesion less soil

A cohesion less soil is a soil that possesses little or no cohesion.

Usually, soils that classify as sands or gravels are considered to be cohesion less. Soil shear strength of sands is described in this article Shear strength of sands.

Cohesive soil

A cohesive soil is usually a fine-grained soil containing greater percentage of clay particles. 

True cohesion can be developed between fine grained soil particles that have been in stationary contact over a long period. Soil shear strength of cohesive soil such as clay is describe in this article Shear strength of Clays.

The first hypothesis on soil shear strength was presented by Coulomb. This hypothesis is described in the following article

Coulomb’s law of shear strength.

Soil shear strength can be determined in the field. However it is most often accomplished in the laboratory by one of three methods.

  1. Triaxial shear test.
  2. Un-confined compression test.
  3. Direct shear test
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