Spt Cpt Correlations: CLAY
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) | n value max (blows/ft) | n value min (blows/ft) | notes | qc max tsf (tsf) | qc min tsf (tsf) | qc typical tsf (tsf) | su psf max (psf) | su psf min (psf) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CLAY | 1 | Very Soft | 4 | 1 | 2 | 0 | Su per Stroud 1974: Su(kPa)=4.4*N60 (Su~N*92 psf); Cv high (fast consolidation) | 5 | 0 | 2.5 | 250 | 0 |
| CLAY | 3.5 | Soft | 10 | 4 | 4 | 3 | Su~N*90-100 psf per Terzaghi & Peck 1967; sensitivity may affect reliability | 10 | 5 | 7.5 | 500 | 250 |
| CLAY | 6 | Medium | 20 | 10 | 8 | 5 | Su per Stroud 1974 Su(kPa)=4.4*N60; N60 used not raw N; OCR typically 1.0-1.5 | 20 | 10 | 15 | 1,000 | 500 |
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