In soil mechanics, stresses are crucial parameters that influence the behavior of soils. The three main types of stresses considered in soil mechanics are:
- Total Stress (σ): Total stress, denoted by the symbol σ (sigma), refers to the total force applied to a soil particle divided by its cross-sectional area. It includes both the weight of the soil particles and any externally applied loads. The total stress is responsible for the initial compression and settlement of the soil.
Mathematically, total stress (σ) can be expressed as: σ = γ * h where γ is the unit weight of the soil and h is the depth of the soil layer.
- Effective Stress (σ'): Effective stress, denoted by the symbol σ' (sigma-prime), represents the portion of the total stress that is transmitted between soil particles and influences the mechanical behavior of the soil. It is the stress that causes soil particles to contact each other and bear the load. In saturated soils, effective stress is a critical factor because it governs the shear strength and consolidation behavior.
Mathematically, effective stress (σ') can be expressed as: σ' = σ - u where σ is the total stress and u is the pore water pressure.
- Neutral Stress (σ_n): Neutral stress, denoted by the symbol σ_n (sigma-n), is the stress at which the soil volume does not change. It is the stress level at which there is no effective stress acting on the soil skeleton, meaning that the pore water pressure counterbalances the total stress. Neutral stress is particularly relevant in the context of consolidation and settlement analysis.
Mathematically, neutral stress (σ_n) can be expressed as: σ_n = u where u is the pore water pressure.
These stress concepts are essential in soil mechanics as they help engineers understand the behavior of soils under different loading conditions, especially during construction projects, foundation design, and slope stability analysis. The interplay between total stress, effective stress, and neutral stress governs the overall response and stability of soil masses.