SPT Allowable Bearing on Sand (Meyerhof)
Meyerhof settlement-controlled allowable from the SPT N60.
Example
You enter
- SPT N60 (energy-corrected) 20
- Footing width B (ft) 6
- Embedment depth D (ft) 2
You get
- Base allowable (before depth factor) 4.54 ksf (wide-footing branch)
- Allowable bearing qa 5.04 ksf
Checked against published worked examples from: PE review notes, 17 Bearing Capacity (civteam).
Details, formula, and sources
Scopeqa = 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 base, 6.10 ksf with Kd 1.22. A 1 in settlement allowable, not the ultimate; N60 energy-corrected. The geotechnical report governs.
Formula or tableqa_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).
Source and editionMeyerhof's (1956) original SPT settlement-based allowable bearing on sand (N/8 and N/12 tsf, i.e. N/4 and N/6 ksf), by name. Bowles' adjusted form -- the one Das, Principles of Foundation Engineering, compiles (about N60/2.5 and N60/4 ksf) -- runs about 50% higher; this tile keeps the conservative original.
Free accessThe Meyerhof N-value allowable-bearing correlations are standard published foundation-engineering results.
What governsEstimate. AHJ and licensed professional govern.
API field namesn60, b_ft, d_ft, qa_base_ksf, qa_ksf
- Allowable bearing N60/4 (B <= 4 ft) or (N60/6)((B+1)/B)^2, x Kd -- Meyerhof's original coefficients; Bowles' adjustment would raise them about 50%Meyerhof (1956)
- Depth factor Kd = min(1 + 0.33 D/B, 1.33)Meyerhof
- Settlement-controlled 1 in settlement allowable; no added FS; N60 energy-correctedscope of this tile