Required SPT N60 for a Target Bearing (Meyerhof)

The energy-corrected N60 the sand must show to carry a target allowable pressure at a 1 in settlement, N60 = qa_target / qa(N60=1). A 6 ft footing 2 ft deep needing 5 ksf wants N60 ~20 (round up for design). A serviceability check against the boring's N-value, not the ultimate bearing. A design aid; the geotechnical report governs.

N60 = qa_target / qa(N60=1), the Meyerhof SPT allowable qa = [N60/4 (B <= 4 ft) or (N60/6)((B+1)/B)^2] x Kd solved for the blow count; Kd = min(1 + 0.33 D/B, 1.33).

The Meyerhof SPT settlement-based allowable bearing on sand solved for the blow count, as compiled in Das, Principles of Foundation Engineering, by name.

The Meyerhof N-value allowable-bearing correlations are standard published foundation-engineering results.

Estimate. AHJ and licensed professional govern.

Field names used by the API: qa_target_ksf, b_ft, d_ft, n60, kd

• Blow count from pressure N60 = qa_target / qa(N60=1), qa linear in N60 in both branchesMeyerhof / Das
• Depth factor Kd = min(1 + 0.33 D/B, 1.33), independent of N60Meyerhof
• Settlement-controlled 1 in settlement check; N60 energy-corrected; round up for designscope of this tile