Enter Project Inputs
Use estimated or measured layer strains. The form uses a three-column grid on large screens, two columns on smaller screens, and one column on mobile.
Example Data Table
| Example | Span (m) | Total Heave (mm) | Total Settlement (mm) | Net Movement (mm) | Absolute Differential (mm) | Status |
|---|---|---|---|---|---|---|
| Warehouse slab edge | 12 | 28.20 | 31.20 | -3.00 | 3.00 | Within limit |
| Light industrial footing | 18 | 42.50 | 30.10 | 12.40 | 12.40 | Near limit |
| Residential strip footing | 9 | 16.80 | 25.60 | -8.80 | 8.80 | Within limit |
Formula Used
Layer Heave (mm) = Layer Thickness (m) × 1000 × Heave Strain (%) ÷ 100 × Heave Adjustment Factor
Layer Settlement (mm) = Layer Thickness (m) × 1000 × Settlement Strain (%) ÷ 100 × Settlement Adjustment Factor
Total Heave = Sum of layer heave values + Seasonal Uplift Allowance
Total Settlement = Sum of layer settlement values + Load Settlement Allowance
Net Movement = Total Heave − Total Settlement
Absolute Differential = |Net Movement|
Angular Distortion = Absolute Differential ÷ (Structure Span × 1000)
Serviceability Use (%) = Absolute Differential ÷ Allowable Differential × 100
How to Use This Calculator
1. Enter the monitored or assumed structure span and the allowable differential movement for the foundation element you are checking.
2. Add heave and settlement adjustment factors when your design method needs correction for moisture variation, load intensity, or local practice.
3. For each soil layer, enter thickness, expected heave strain, and expected settlement strain. Leave unused layers at zero.
4. Include seasonal uplift and load settlement allowances when you want the comparison to reflect extra movements outside the layered strain model.
5. Click Compare Movements. The result appears above the form and shows movement totals, net response, distortion, and serviceability status.
6. Export the result summary using the CSV or PDF buttons for reports, site records, design reviews, or client communication.
FAQs
1. What does this calculator compare?
It compares predicted upward soil heave against predicted downward settlement. The tool totals both movements, finds the net response, and checks whether differential movement remains within the selected serviceability limit.
2. When is heave more critical than settlement?
Heave becomes more critical when expansive soils, moisture changes, or uplift effects create upward movement larger than downward compression. This can distort slabs, crack finishes, and lift lightly loaded foundations.
3. Can I use field measurements instead of estimated strains?
Yes. You can convert measured movement tendencies into equivalent layer strain percentages or adjust the allowance fields to reflect observed seasonal uplift and load-related settlement from site monitoring.
4. Why is span included in the calculation?
Span converts movement difference into angular distortion. A small differential over a short span can be more damaging than the same differential over a long span.
5. What is a movement ratio?
The movement ratio is total heave divided by total settlement. Values above one indicate heave dominates. Values below one indicate settlement dominates. It offers a quick directional check, not a design code replacement.
6. How should I choose the adjustment factors?
Use factors from your geotechnical method, project criteria, or local calibration. Keep them at 1.00 when no correction is needed. Increase them only when justified by analysis or measured site behavior.
7. Does this replace a geotechnical report?
No. It is a comparison and screening tool. Final design decisions should still follow project geotechnical recommendations, code requirements, structural detailing, and site-specific investigation results.
8. What does an exceeds limit status mean?
It means the absolute differential movement is greater than the allowable value you entered. Review soil assumptions, detailing, stiffness, moisture control, and foundation type before finalizing design decisions.