Geotechnical correlations¶
What they are¶
Geotechnical correlations transform N_SPT into soil strength and deformability parameters. They are empirical formulas derived from international literature — their use is well established in geotechnical practice, but they remain estimates: always supplement with laboratory data when available.
How to read them¶
In the Correlations tab of the Editor, for each layer in the stratigraphy a table appears with the computed values. The left column indicates the parameter; the subsequent columns show the values according to the different reference authors. You can activate or deactivate individual authors using the toggles at the top of each column.
The preferred value (⭐) feeds the Parameter summary tab and the Word report.
Parameters for cohesive soils (COES)¶
| Parameter | Meaning |
|---|---|
| Cu | Undrained shear strength (kPa) |
| Mo | Oedometric modulus (MPa) |
| Ey | Young's modulus (MPa) |
| Vs | Shear wave velocity (m/s) |
| γ | Unit weight (kN/m³) |
| Classification | Consistency (very soft → very stiff) |
Reference authors cited in Italian and international geotechnical literature: Terzaghi-Peck, Schmertmann, Ohta-Goto, and others.
Parameters for non-cohesive soils (INCO)¶
| Parameter | Meaning |
|---|---|
| Dr | Relative density (%) |
| φ | Internal friction angle (°) |
| φ_160 | Friction angle from normalised N_1,60 (°) |
| Mo | Oedometric modulus (MPa) |
| Ey | Young's modulus (MPa) |
| Vs | Shear wave velocity (m/s) |
| ν | Poisson's ratio |
| G | Shear modulus (MPa) |
Reference authors: Meyerhof, Peck, Hanson, Thornburn, Ohta-Goto, Seed-Idriss, and others.
Validity limits
Each correlation was developed for a specific range of N_SPT and specific soil types. When N_SPT is very low (< 3) or very high (> 50), results should be interpreted with caution. The app highlights out-of-range values.
Parameter envelope¶
When you have multiple tests on the same site, the Envelope tab shows for each layer the min-max range of parameters across all tests, with the design criterion selectable (minimum / mean / maximum / preferred value ⭐). The design value automatically feeds the Summary.
Parameter summary¶
The Summary tab collects in a single table the characteristic geotechnical values for each layer — useful as a overview table to include in the geotechnical report. The Word report includes it automatically.