Maximum/minimum soil pressure is the highest and lowest contact pressures developed between the bottom of a footing and the supporting soil. For a footing carrying an axial vertical load together with a moment, the pressure beneath the footing is generally nonuniform because the load is eccentric relative to the footing centroid. FHWA guidance identifies these quantities as the maximum bearing pressure, and minimum bearing pressure, .
Maximum/minimum Soil Pressure Formulas |
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\( q_{max} \;=\; \dfrac{ P }{ A } \cdot \left( 1 + \dfrac{ 6 \cdot e_{load} }{ B } \right) \) (Maximum Soil Pressure) \( q_{max} \;=\; \dfrac{ 2 \cdot P }{ 3 \cdot L \cdot \left( \left( \dfrac{ B }{ 2 } \right) \cdot e_{load} \right) } \) (Maximum Soil Pressure)
\( q_{min} \;=\; \dfrac{ P }{ A } \cdot \left( 1 - \dfrac{ 6 \cdot e_{load} }{ B } \right) \) (Minimum Soil Pressure) \( q_{min} \;=\; \left( \dfrac{ P }{ b \cdot L } \right) \cdot \left( 1 - \left( \dfrac{ 6 \cdot e_{load} }{ b } \right) \right) \) (Minimum Soil Pressure) |
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| Symbol | English | Metric |
| \( q_{max} \) = Maximum Soil Pressure | \(psf\) | \(Pa\) |
| \( q_{min} \) = Minimum Soil Pressure | \(psf\) | \(Pa\) |
| \( P \) = Service Load on Footing | \(lbf\) | \(N\) |
| \( A \) = Footiing Area | \(ft^2\) | \(m^2\) |
| \( e_{load} \) = Load Eccentricity | \(ft\) | \(m\) |
| \( B \) = Footing Width | \(ft\) | \(m\) |
| \( L \) = Footing Length (the Dimension in the Direction the Wind is Blowing. It Resists the Overturning Moment.) | \(ft\) | \(m\) |
| \( b \) = Footing Width (the Dimension Along the Length of the Wall Itself) | \(ft\) | \(m\) |
