Spt Cpt Correlations: GRAVEL
SPT blow count (N-value) and CPT cone resistance (qc) correlations to engineering properties — friction angle, relative density, undrained shear strength, and elastic modulus by soil type and density class
| soil type | n value mid | density consistency | elastic modulus tsf max (tsf) | elastic modulus tsf min (tsf) | friction angle deg max (deg) | friction angle deg min (deg) | friction angle deg typical (deg) | n value max (blows/ft) | n value min (blows/ft) | notes | qc typical tsf (tsf) | relative density pct max (%) | relative density pct min (%) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| GRAVEL | 5 | Loose | 150 | 60 | 32 | 28 | 30 | 10 | 0 | qc less reliable in gravel; N60 preferred; phi per Kulhawy & Mayne 1990 | 25 | 40 | 15 |
| GRAVEL | 20 | Medium Dense | 350 | 150 | 36 | 32 | 34 | 30 | 11 | Gravel: phi typically 2-4 deg higher than sand at same Dr; Es per Kulhawy & Mayne 1990 | 80 | 65 | 40 |
| GRAVEL | 40 | Dense | 600 | 350 | 40 | 36 | 38 | 50 | 31 | N60 correction factor CN = (Pa/sigma_v)^0.5 per Liao & Whitman 1986 | 200 | 85 | 65 |
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