Vertical Effective Stress
Vertical Effective Stress
Effective stress — the stress carried by the soil skeleton — governs strength and settlement; it is the total stress minus pore-water pressure.
At depth, σ′ = γ·z − γ_w·z_w. where γ is the soil unit weight, z the depth, γ_w the water unit weight and z_w the depth below the water table.
Inputs
gamma := 19 kN/m^3=19000 kg/m^2/s^2
z := 6 m=6 m
gamma_w := 9.81 kN/m^3=9810 kg/m^2/s^2
z_w := 4 m=4 m
Subtract pore pressure from total stress.
sigma_eff := gamma·z - gamma_w·z_w=74760 Pa
Results
Effective stress rises with depth but the water table reduces it. Lowering the water table (e.g. by pumping) increases effective stress and can cause settlement.
Assumptions & limitations
- Hydrostatic pore pressure.
- Saturated below the water table.
- Single soil unit weight.