SPT Data Tab
Deep Dive
Import, view, and analyze Standard Penetration Test data. Automatic N60 corrections, friction angle calculations using multiple methods, and engineering parameter estimation.
Interface Overview
The SPT Data tab provides comprehensive data management with industry-standard corrections:
- Data point count, depth range, and action buttons (Settings, Export, Import, Add Point).
- Equipment parameters (borehole diameter, sampler type, hammer energy) and column visibility toggles.
- Quick statistics: data points count, depth range, average N, maximum N.
- Full data grid with blow counts, corrections, and engineering parameters.
Equipment Parameters
Before analyzing SPT data, configure the equipment parameters that affect correction factors:
Borehole Parameters
| Parameter | Options | Correction |
|---|---|---|
| 65-115 mm | ||
| 150 mm | ||
| 200 mm |
Sampler Type
| Type | Description | Correction |
|---|---|---|
| Standard sampler | ||
| Sampler without liner | ||
| Sampler without liner |
Rod Length Correction (CR)
| Depth | Correction |
|---|---|
| RodLess3m | |
| Rod3to4m | |
| Rod4to6m | |
| Rod6to10m | |
| RodGreater10m |
EquipmentAccess
EquipmentConfig
Understanding Data Columns
Data columns are organized into four categories:
Blow Counts (Editable)
| Column | Unit | Description |
|---|---|---|
| Test depth from surface | ||
| Calibration blows (first 15 cm, seating) | ||
| Second 15 cm blow count | ||
| Third 15 cm blow count | ||
| Total N value (N2 + N3) | ||
| Energy ratio (default 60%) |
Soil Parameters (Editable)
| Column | Unit | Description |
|---|---|---|
| Dry unit weight of soil | ||
| Saturated unit weight of soil | ||
| Select from stratigraphy layers |
Corrected Values (Read-Only)
| Column | Unit | Description |
|---|---|---|
| Energy-corrected N value (N × ER/60) | ||
| Height of dry soil column | ||
| Height of saturated soil column | ||
| Total vertical stress | ||
| Pore water pressure | ||
| Effective vertical stress |
Engineering Parameters (Read-Only)
| Column | Unit | Description |
|---|---|---|
| Overburden-corrected N60 | ||
| CPT equivalent cone resistance | ||
| Friction angle (Jamiolkowski method) | ||
| Friction angle (Hatanaka-Uchida) | ||
| Friction angle (Wolff method) | ||
| Relative density (Kulhawy & Mayne) | ||
| Relative density (Skempton) | ||
| Minimum elastic modulus | ||
| Maximum elastic modulus | ||
| Ultimate bearing capacity |
N60 Energy Correction
The N60 value normalizes SPT blow counts to 60% energy efficiency:
| Factor | Description |
|---|---|
| Energy ratio of hammer (typically 45-80%) | |
| Borehole diameter correction | |
| Sampler type correction | |
| Rod length correction |
Friction Angle Calculations
Borebase calculates friction angle using three established methods:
Jamiolkowski et al. (1988)
Best for normally consolidated sands. Uses overburden-corrected N value.
Hatanaka & Uchida (1996)
Widely used correlation for granular soils. Simple and reliable.
Wolff (1989)
Uses N60 directly without overburden correction. Good for general applications.
Relative Density Estimation
Two methods for estimating relative density of granular soils:
Kulhawy & Mayne (1990)
Uses overburden-corrected N1 value. Suitable for clean sands.
Skempton (1986)
Accounts for vertical effective stress. Coefficients a and b depend on soil type.
| Column | Description |
|---|---|
| Very Loose | |
| Loose | |
| Medium Dense | |
| Dense | |
| Very Dense |
Elastic Modulus Estimation
The elastic modulus range is estimated from N60 values:
Importing SPT Data
Import SPT data from CSV or Excel files:
ImportStep1
ImportStep2
ImportStep3
ImportStep4
ImportStep5
ImportStep6
ImportStep7
Soil Type Selection
Link SPT data points to stratigraphy layers for automatic unit weight assignment:
- Click the Soil Type dropdown for any data row.
- Select from available stratigraphy layers defined in the Strata tab.
- Unit weights (γ dry, γ sat) are automatically populated from the layer properties.
- All stress calculations update automatically.
AddPoint
AddPointIntro
AddPointStep1
AddPointStep2
Settings
SettingsIntro
SettingsCalc
SettingsColumns
SettingsExportVisible
Exporting SPT Data
Export your SPT data with all calculations for reports:
ExportStep1
ExportStep2
- All visible columns in comma-separated format. Open in Excel, Python, or any data tool.
- Professional formatting with styled headers, proper column widths, and formulas preserved.
Best Practices
Data Entry
- Always enter the calibration blows (N1c) even though they're not used in N calculation.
- Verify energy ratio with your testing equipment - don't assume 60%.
- Link data points to stratigraphy layers for consistent unit weights.
Quality Control
- Watch for refusal values (N > 50) which may indicate hitting bedrock or very dense layers.
- Check for unit weight warnings (yellow triangle icons).
- Compare friction angles from different methods - large discrepancies may indicate issues.
Interpretation
- SPT correlations work best for sands and gravels. Use caution with clays.
- Consider using the conservative (lower) friction angle for design.
- Elastic modulus ranges are wide - use laboratory tests for important projects.