Soil Vertical Total and Effective Stress (Terzaghi)
The effective stress three other tiles here make you work out by hand. Total stress is everything stacked above the point (surcharge, then moist soil to the water table, then saturated soil below); pore pressure below the table is hydrostatic u = 62.4 x depth below it; and Terzaghi's sigma' = sigma - u is what the soil skeleton actually carries. At 20 ft in a 120/125 pcf profile with the table at 10 ft: 2,450 psf total, 624 psf pore, 1,826 psf effective. Below the table that equals stacking the BUOYANT unit weight (125 - 62.4 = 62.6 pcf), which is why submerged soil weighs about half and why moving a water table shifts settlement and bearing capacity with no load change at all. A surcharge raises total and effective equally since it adds no pore pressure. Feed the results straight into liquefaction-screening and soil-consolidation-settlement. Hydrostatic, level ground, uniform layers. A design aid; the geotechnical engineer of record governs.
Formula and source
z_dry = min(z, z_wt); z_sub = max(0, z - z_wt); sigma_v = q + gamma_moist x z_dry + gamma_sat x z_sub; u = gamma_w x z_sub (gamma_w = 62.4 pcf); sigma'_v = sigma_v - u. Below the table this equals q + gamma_moist x z_wt + (gamma_sat - gamma_w) x z_sub.
Terzaghi's effective-stress principle and the hydrostatic vertical stress profile, as compiled in Das, Principles of Foundation Engineering, and NAVFAC DM-7.01 (Soil Mechanics), by name.
Audience
This tile is built for trades and the adjacent professions in the Carpentry and Construction group. The interactive calculator runs entirely in your browser. No account, no fee, no advertising, no tracking.
Related tools
Posture
Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.