Quick Answer
Use the Earth Pressure (Coulomb) Calculator to estimate active earth force using a simplified Coulomb active pressure coefficient. In plain terms, enter Soil Friction Angle (deg), Wall Friction Angle (deg), Soil Unit Weight (kN/m3), Wall Height (m) and the calculator returns Active earth force with supporting values where the formula produces them.
This page is built for civil engineers, geotechnical reviewers, pavement analysts, students, and field teams. It is most useful for early soil, groundwater, lateral earth pressure, settlement, and pavement loading checks where site data is already known. The calculator keeps every input unit visible, shows the governing equation, and separates formula math from design approval so humans, search engines, and AI agents can understand exactly what is being computed.
Formula
The formula block above is the calculation used by the tool. The variable list below the equation defines the symbols in the same context as the calculator fields, so you can audit the math before relying on the result.
How to Use This Calculator
- Enter each known value using the unit printed beside the field. For this calculator, common starting inputs include Soil Friction Angle (deg), Wall Friction Angle (deg), Soil Unit Weight (kN/m3), Wall Height (m).
- Confirm that coefficients, material properties, pressure basis, and geometry match the real system you are checking.
- Read the primary output first, then review any secondary values for intermediate checks or interpretation.
- Change one input at a time when comparing alternatives. This makes sensitivity checks easier and helps identify which assumption controls the result.
- Save or share the calculator URL after entering non-default values if you need a repeatable calculation record.
Inputs and Units
| Input | Unit | Default | Why it matters |
|---|---|---|---|
| Soil Friction Angle | deg | 30 | Represents a material property, coefficient, or empirical factor that should come from reliable data. |
| Wall Friction Angle | deg | 10 | Represents a material property, coefficient, or empirical factor that should come from reliable data. |
| Soil Unit Weight | kN/m3 | 18 | Defines the applied demand or transfer rate used by the equation. |
| Wall Height | m | 4 | Defines the geometry, size, or flow area that strongly affects the result. |
Example Workflow
A practical workflow is to start with the default values, replace Soil Friction Angle with your project value in deg, then update the remaining inputs from drawings, field measurements, lab data, supplier tables, or project specifications. After the result updates, compare it with an independent hand check and with any project limits that apply to the same load case or operating condition.
For AI agents and spreadsheet workflows, use the exact input IDs from the public manifest or API payload contract rather than guessing from the visible labels. This prevents unit mix-ups and keeps the calculation reproducible.
Result Interpretation
The primary result is Active earth force. In geotechnical and civil engineering, small changes in soil parameters can create large changes in capacity, pressure, flow, or settlement, so sensitivity checks are especially important. A result that looks unexpectedly high, low, or sensitive to a small input change is usually a signal to check units, assumptions, boundary conditions, and the valid range of the equation before moving on.
Use this output as a transparent engineering calculation, not as a hidden design decision. For safety-critical or regulated work, document the input source, the formula assumption, the applicable standard, and the review path.
Assumptions and Limits
- Soil parameters are representative of the layer, drainage condition, and loading condition being checked.
- The calculation does not replace borings, lab testing, groundwater monitoring, geotechnical reporting, or pavement design standards.
- Layering, surcharge, seismic loading, slope geometry, construction disturbance, and long-term groundwater changes may control the actual design.
- The calculator does not add hidden safety factors, resistance factors, load combinations, code allowances, inspection requirements, or permit rules.
Common Mistakes
- Entering total stress where the formula expects effective stress.
- Using a single soil unit weight or friction angle for a layered profile.
- Reading a screening value as a foundation, wall, or pavement design approval.
- Entering values with the right number but the wrong unit, such as using mm where m is expected or using a nominal dimension where an internal dimension is required.
References and Further Checks
These references are useful for context and validation, but the calculator itself remains a simplified formula tool:
- FHWA Pavement Resources - pavement and ESAL context for transportation checks.
- FHWA Geotechnical Engineering - geotechnical engineering references for project-level review.
For final engineering decisions, compare the result with governing codes, manufacturer data, site-specific measurements, and professional judgment.