SPT Allowable Bearing on Sand (Meyerhof)
Meyerhof settlement-controlled allowable from the SPT N60: qa = N60/4 ksf for B <= 4 ft else (N60/6)((B+1)/B)^2, times Kd = min(1 + 0.33 D/B, 1.33). N60 20, B 6, D 2 -> 4.54 base, Kd 1.11, 5.04 ksf; a 3 ft footing gives 5.00 ksf. A 1 in settlement allowable, not the ultimate; N60 energy-corrected. The geotechnical report governs.
Formula and source
qa_base = N60/4 (B <= 4 ft) or (N60/6)((B+1)/B)^2; Kd = min(1 + 0.33 D/B, 1.33); qa = qa_base Kd (ksf, 1 in settlement).
The Meyerhof SPT settlement-based allowable bearing on sand, as compiled in Das, Principles of Foundation Engineering, by name.
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