Skip to content
ENGNIO

Engineering tools

Allowable bearing pressure for footings from SPT data

Enter the SPT profile, footing dimensions and founding depth. Compare allowable bearing pressures from the selected methods and examine the failure mode and estimated settlement.

Open the tool

The app and these introductory pages are available in Portuguese, English and Spanish.

What the tool calculates

  • Comparison of Terzaghi, Brinch Hansen, Vesić and Meyerhof, using each method's own bearing capacity factors
  • Progressive reduction of c and tanφ to account for the failure mode when parameters are derived from SPT data
  • Weighted average SPT N-value within the influence zone extending 1.5B below the base
  • Settlement estimate and an indication of suitability or caution for each method

What you enter

  • SPT profile
  • Footing plan dimensions and founding depth
  • Theoretical methods to compare

What you receive

  • Allowable bearing pressure for each method
  • Failure mode used in the calculation
  • Settlement estimate and an indication of suitability or caution

References and limits of applicability

  • ABNT NBR 6122:2019 + Emenda 1:2022 — Foundation design and construction (§6.2.1, allowable bearing pressure and settlement)

Checks and considerations

  • Local or punching shear failure in loose or soft soils
  • Settlement above the guidance limit

How it works

Geotechnical bearing capacity is calculated using soil strength parameters and the factors of the selected method. When parameters are derived from SPT data, the model considers the N-values in the influence zone and the reduction associated with the failure mode. The adopted pressure must also satisfy settlement requirements. This tool does not design footing reinforcement.

Example of use

To study an isolated footing, enter the borehole data and founding depth, then compare alternative widths. Review allowable bearing pressure, settlement and warnings before taking the selected geometry into structural design.

Frequently asked questions

Why do the methods give different results?

The methods use different assumptions and bearing capacity factors. Assess their results against the soil conditions, geometry, failure mode and settlement. The final choice depends on the designer's assessment.

Generated documents

These documents are assembled within your project using data from the corresponding tools.

  • Foundation calculation report — Combine the project's SPT logs, bearing capacity calculations and structural designs for piles, pile caps, footings and belled caissons in one PDF. The document consolidates selected items; technical checks remain within each tool.

Explore other tools