Stratigraphy and water table¶
The stratigraphy describes the soil below the founding plane, layer by layer. The quality of the calculation depends directly on the quality of these parameters.
Per-layer parameters¶
Each row of the Stratigraphy table has the main fields always visible and the deformability parameters in the detail panel (arrow on the left).
| Symbol | Unit | Meaning |
|---|---|---|
| s | m | Layer thickness |
| γ | kN/m³ | Natural unit weight |
| γ_sat | kN/m³ | Saturated unit weight (below the water table) |
| φ′ | ° | Effective shear resistance angle |
| c′ | kPa | Effective cohesion |
| c_u | kPa | Undrained cohesion (total-stress analysis) |
| E | kPa | Elastic modulus (elastic and Schmertmann settlements) |
| E_ed | kPa | Oedometric modulus (oedometric settlements) |
| ν | – | Poisson's ratio |
| C_s | – | Secondary consolidation coefficient |
| C_v | – | Primary consolidation coefficient (time curve) |
| N_SPT | – | SPT blow count (Burland & Burbidge method) |
SI units, case-sensitive
Symbols are in SI units and follow scientific conventions: kPa, MPa, kN/m³. Be careful not to confuse γ (unit weight, kN/m³) with pressures (kPa).
Which parameters are used for what¶
- Bearing capacity: γ, φ′, c′ (drained) or c_u (undrained).
- Elastic settlements: E, ν.
- Oedometric settlements: E_ed (and C_v for the time curve, C_s for the secondary part).
- Burland & Burbidge settlements: N_SPT.
If a layer has E_ed > 0 it is treated with the oedometric method; without E_ed,
if E > 0, with the Schmertmann method. See Settlements.
Paste and import¶
Filling the stratigraphy by hand is not the only way:
- Paste — copy a table from an Excel sheet (or from the desktop grid) and paste it: a dialog lets you map the columns onto the fields. Layer colours are assigned with an earthy gradient from light (top) to dark (bottom).
- Import — load a stratigraphy in JSON format, typically exported from
Dynamic Probing NX ("Export for Loadcap"), or a
.lcnxfile.
From test data to stratigraphy
For a stratigraphy derived from penetration tests, the rigorous interpretation belongs to Dynamic Probing NX: from there you export the already characterised layers (γ, φ′, c_u, E, N_SPT) ready for Loadcap.
Water table¶
In the Water table card you set:
- Water table presence — absent or present;
- Depth from ground level — positive below ground level.
The water table governs the calculation of effective stresses (uplift) and, therefore, both the bearing capacity and the settlements. Below the water table the γ_sat unit weight is used.
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