Net bearing pressure is the increase in vertical pressure, or vertical effective stress, applied to the soil at the elevation of the bottom of a foundation due to the foundation and structural loading, after accounting for the vertical stress that already existed at that elevation before construction. For foundation design, it is important to distinguish net bearing pressure from net allowable bearing pressure. Net bearing pressure is the actual applied pressure increase produced by the foundation and structure. Net bearing pressure is the additional pressure imposed on the soil at the footing level above the soil's pre-existing vertical effective stress. It is particularly useful for spread footing and shallow foundation design because it accounts for the stress relief caused by excavation before the foundation load is applied.
Net Bearing Pressure Formulas |
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\( q_{net} \;=\; q - \gamma \cdot D_f \) (Net Bearing Pressure) \( q_{net} \;=\; \dfrac{ P }{ A } - \gamma \cdot D_f \) (Net Bearing Pressure) |
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| Symbol | English | Metric |
| \( q_{net} \) = Net Bearing Pressure | \(psf\) | \(Pa\) |
| \( q \) = Gross Bearing Pressure | \(psf\) | \(Pa\) |
| \( \gamma_d \) (Greek symbol gamma) = Unit Weight of Soil | \(lbm \;/\; ft^3 \) | \( N \;/\; m^3 \) |
| \( D_f \) = Depth of Footiing | \(ft\) | \(m\) |
| \( P \) = Service Load on Footing | \(lbf\) | \(N\) |
| \( A \) = Footiing Area | \(ft^2\) | \(m^2\) |
