What is the difference between total and effective stress?
Total Stress vs Effective Stress
Total Stress: This is the sum of all stresses acting on a soil mass, including the weight of the soil particles, the weight of any structures or objects on the soil, and any external forces applied to the soil. Total stress is a measure of the total force exerted on the soil.
Effective Stress: Effective stress takes into account the interparticle forces within the soil mass. It excludes the pore water pressure and represents the stress that is actually carried by the soil particles themselves, influencing the mechanical behavior of the soil.
Importance of Effective Stress
Effective stress is crucial in geotechnical engineering because it governs the strength and deformation characteristics of soils. By understanding the effective stress acting within a soil mass, engineers can predict how the soil will behave under different loading conditions, such as during the construction of buildings or infrastructure.
Calculation of Effective Stress
The formula to calculate effective stress in saturated soils is:
σ' = σ - u
Where:
σ' = Effective Stress
σ = Total Stress
u = Pore Water Pressure
In unsaturated soils, the calculation of effective stress becomes more complex due to the presence of both water and air in the soil voids. Factors such as degree of saturation and capillary forces impact the effective stress in these conditions.
Understanding the difference between total stress and effective stress is essential in geotechnical engineering for accurate analysis and design of structures built on or in contact with soil.