How to use the foundation settlement calculator
A shallow footing that passes the bearing check can still fail on serviceability. This calculator uses the elastic settlement equation Se = q·B·(1−ν²)·If / Es to estimate the settlement that appears as soon as the load is applied. The influence factor If depends on footing shape and rigidity, so pick the standard tabulated value: 1.12 for the center of a flexible square, 0.82 for a rigid square, and so on.
Settlement grows with bearing pressure and footing width, and shrinks as the soil modulus rises. Widening a footing helps the bearing check but can increase elastic settlement, which is why both checks are run together. The table below gives screening ranges for the soil modulus.
| Soil | Es range (ksf) |
|---|---|
| Loose sand | 200 ~ 520 |
| Dense sand and gravel | 1,050 ~ 2,100 |
| Soft clay | 85 ~ 420 |
| Stiff clay | 420 ~ 1,050 |
In clay, consolidation settlement follows the immediate component and often dominates, so never judge a clay site on this number alone. Differential settlement between columns damages structures more than uniform total settlement, so compare adjacent footings as well. Treat the output as a screening estimate based on a uniform elastic half-space, and have a licensed geotechnical engineer confirm the final design with site boring data.
Frequently asked questions
Immediate (elastic) settlement happens as soon as the load is applied, as the soil skeleton distorts. Consolidation settlement develops over months or years as pore water drains out of clay. This calculator covers the immediate component only.
About 1 inch of total settlement is a common rule of thumb for isolated footings on sand. What actually damages a structure is differential settlement between columns, so check that separately even when total settlement looks fine.
Use pressuremeter or triaxial test results from the geotechnical report whenever possible. Values estimated from SPT correlations scatter widely, so treat them as a screening figure rather than a design input.