Bearing capacity from plate load curve

The load–settlement curve of a plate load test on sand is plotted as pressure $q$ against settlement $s$.

1. Ultimate bearing capacity of the plate $q_{up}$: take the pressure at the point of failure (peak). If the curve has no clear peak, use the intersection of tangents drawn to the initial and the final straight parts of the curve (or the break point on a log–log plot).
2. Footing capacity: in sand, $q_u$ increases with width, so $q_{u}(\text{footing}) = q_{up}\dfrac{B}{B_p}$.
3. Safe bearing capacity (shear): $q_s = q_u/F$ with $F = 2.5$ to $3$.
4. Settlement criterion: for the permitted settlement of the footing (25 mm), the equivalent plate settlement is found from $\dfrac{S_f}{S_p} = \left[\dfrac{B(B_p+0.3)}{B_p(B+0.3)}\right]^2$, and the pressure for that plate settlement is read from the curve.
5. The allowable bearing pressure is the smaller of the safe pressure by shear failure and the pressure by settlement.