| Scenario | Units | Eff. depth | Material | Moisture | Passes | Target | Risk | Tol | Typical output* |
|---|---|---|---|---|---|---|---|---|---|
| Granular base, near optimum | mm | 250 | 1.00 | 1.00 | 6 | 95% | Low | 10% | ~200–260 mm range |
| Silty fill, slightly wet | mm | 200 | 0.90 | 0.95 | 4 | 95% | Medium | 10% | ~110–145 mm range |
| Plastic clay, wet conditions | mm | 200 | 0.80 | 0.90 | 6 | 98% | High | 12% | ~70–100 mm range |
| Imperial check, granular | in | 10 | 1.00 | 1.00 | 6 | 95% | Low | 10% | ~8–10 in range |
The recommended maximum lift thickness per pass is estimated using:
Pf = pass factor (diminishing returns); Tf = target factor; Sf = safety factor.
Tolerance limits are calculated as:
- Select the unit system used on your drawings and reports.
- Enter the effective compaction depth from your roller or rammer.
- Pick a material factor that matches the fill behavior.
- Choose the moisture condition based on field observations.
- Set planned compaction passes and target compaction percentage.
- Select a risk category or enable a custom safety factor.
- Set the tolerance percentage to define acceptable variability.
- Click Calculate to display results and save history.
- Use Download CSV for spreadsheets and reporting.
- Use Download PDF for quick site sharing.
- Run multiple scenarios to compare lifts before field trials.
Why Lift Thickness Controls Performance
Lift thickness drives how compaction energy reaches the full layer. If a layer is too thick, the lower zone can stay loose even when surface density looks acceptable. For planning, many teams start with working bands such as 75–150 mm for cohesive fills and 150–300 mm for well-graded granular fills, then confirm using a test strip. Field checks like probe readings and gauge readings can reveal under-compaction early, before the next lift locks defects in place.
Interpreting Effective Compaction Depth
Effective depth is the thickness a specific machine can compact reliably under ideal conditions. It depends on drum size, frequency, amplitude, contact pressure, and the soil response. Treat this value as a ceiling, not a guarantee. If your equipment depth is 200 mm, designing lifts near 200 mm may still fail if moisture, gradation, or access constraints reduce energy transfer.
Material and Moisture Adjustments
Granular materials typically accept thicker lifts because particles reorient and densify with fewer passes. Cohesive soils often need thinner lifts to avoid “bridging” and trapped water. Moisture near optimum supports lubrication and rearrangement; wet conditions reduce friction and can cause pumping, while very dry cohesive fills may resist kneading. Using factors helps compare scenarios consistently before field verification.
Using Tolerance Bands for Acceptance
Tolerance turns a single recommendation into an actionable range. A ±10% band is common for planning because it reflects small variations in grading and moisture, while tighter bands like ±5% can be used where rework cost is high or density targets are strict. The range helps crews keep lifts inside a measurable window and supports quick corrective decisions.
Turning Results into a Field Plan
Convert the recommended lift into clear site instructions: target thickness, minimum and maximum limits, pass count, and moisture checks. For example, a 120 mm recommended lift with ±10% tolerance becomes 108–132 mm with 6 passes. Record each run in the history table, export CSV for daily reports, and keep PDF summaries for inspection files.
1) Is this result a specification value?
No. It is a planning estimate. Always follow project specifications, geotechnical recommendations, and equipment guidance. Use the output to design a test strip and adjust lift thickness based on density results.
2) What tolerance should I use?
Start with ±10% for general planning. Use ±5% for tight control areas or high-risk rework zones. Increase only when variability is unavoidable and inspection criteria allow it.
3) Why does higher target compaction reduce lift?
Higher targets usually require more uniform energy through the layer. Thinner lifts reduce weak zones and make it easier for the full depth to reach the required density.
4) How many passes should I choose?
Many sites plan 4–8 passes, then tune using test-strip density and roller pattern checks. Extra passes help, but benefits diminish, especially when moisture or material limits performance.
5) When should I use a custom safety factor?
Use it when you have strong site-specific evidence, such as trial data, experienced operator feedback, or unusual risk conditions. Lower values add conservatism; higher values should be justified by testing.
6) Does switching units convert existing inputs?
No. The unit selector changes labels and output units only. Convert your numbers manually when switching between millimeters and inches to avoid accidental scale errors.