\[\sigma'=\sigma-u\]
Variables
sigmae[σ']effective stress (Pa)
sigma[σ]total stress (Pa)
upore water pressure (Pa)
Description
What is this formula?
The Effective Stress equation, introduced by Karl Terzaghi, calculates the portion of the total stress that is actually carried by the soil skeleton.
It is one of the most important concepts in geotechnical engineering because soil strength, settlement, and deformation depend primarily on effective stress rather than total stress.
When to use it
Use this formula when analyzing:
- Foundations
- Retaining walls
- Embankments
- Consolidation problems
- Slope stability
- Groundwater effects
Example
A soil layer is subjected to:
σ = 250 kPa
u = 90 kPa
Formula:
σ' = σ - u
Substitution:
σ' = 250 - 90
σ' = 160 kPa
Result:
σ' = 160 kPa
Applications
- Foundation design
- Bearing capacity calculations
- Settlement analysis
- Earth pressure analysis
- Slope stability
- Geotechnical investigations