Online soil movement calculator

AS 2870 characteristic surface movement calculator

Choose the site profile. For soil sites, enter layer depths and laboratory-tested shrink-swell index (Iss) values to estimate characteristic surface movement, ys, and an indicative site classification for Melbourne conditions. Contiguous rock cleared of soil follows a separate indicative Class A path.

Indicative calculatorResults depend on the information entered and are not a soil test or signed site classification report.

Site and soil inputs

Choose the site profile

What type of site are you assessing?
Choose the option that describes the whole site.

The calculator is currently unavailable.

Indicative calculation result

Characteristic surface movement

Professional confirmation requiredConfirm the site profile and result before using it for design, approval, or construction.
ys—
Indicative site class—

Select the type of site being assessed to begin.

Climate zone
Melbourne
Hs used
—
hc used
—
Surface Δu
—

Per-layer contribution

Unrounded inputs are used internally; these values are formatted for presentation.
Layer depthSoilIssαAverage ΔuEffective hContribution
Layer contributions will appear after the calculation is completed.
Total ys—
Class P conditions are not included in this result. This includes trees, abnormal moisture conditions, fill, erosion, and other problem-site effects.

Site-specific support

Need a soil test, report or site classification?

Request a site-specific assessment from Soil Test Melbourne.

Request a soil test or quotation

Frequently asked questions

About the surface movement calculator

For a soil profile, the calculator estimates characteristic surface movement by adding the calculated contribution from each soil layer within the selected design depth. Each contribution uses the laboratory-tested shrink-swell index (Iss), lateral-restraint factor, average soil-suction change, and effective layer thickness.

For contiguous rock cleared of soil, no soil-movement calculation is performed. The tool displays Indicative Class A with ys as Not calculated.

ys = 1/100 × Σ(α × Iss × average Δu × h)n

Enter depths in metres. Effective layer thickness is converted to millimetres for the calculation. The displayed ys is truncated to one decimal place, while the exact unrounded value is used for site classification.

For a soil profile, use the laboratory shrink-swell index (Iss) reported by the supporting shrink-swell test, together with its corresponding sample depth and soil description. Values must be expressed in %/pF. Do not estimate or convert missing values. You must also select the site location relative to Plenty Road and enter the soil-layer depths and material classifications.

  • Tree-related soil movement or Appendix H effects
  • Abnormal moisture or Class P site conditions
  • Fill, erosion, groundwater, or drainage effects
  • Site-specific geology outside the supplied soil data
  • Footing design or construction requirements

A calculator cannot assess the complete site context. Sampling quality, geology, fill, groundwater, drainage, trees, abnormal moisture conditions, and proposed construction require site-specific professional judgement. The result should be confirmed by a qualified geotechnical professional before it is used for design, approval, or construction.

Characteristic surface movement, ys, is a calculated movement value in millimetres based on the contribution of soil layers within the selected design depth. It is one input to residential site assessment and footing design.

The calculator sorts valid layers by top depth and does not accept overlapping layers. Gaps contribute zero and generate a warning. Portions of layers below the selected design depth are excluded from the calculation.

Select this only when the whole site consists of contiguous rock cleared of soil. The calculator will show Indicative Class A without calculating characteristic surface movement.

Important disclaimer

This calculator provides an indicative estimate based solely on the information entered. It does not account for every site condition and is not a soil test, site classification report, engineering certification, or design advice. Do not rely on the result as the sole basis for footing design, construction, or approval decisions. Obtain a site-specific investigation and written advice from a suitably qualified geotechnical professional.

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