Bearing Capacity of Soil and Foundations

Bearing capacity describes the ground's ability to support foundation loading without an unacceptable shear failure or ground deformation. It is one part of foundation design and should be assessed together with settlement, footing geometry, groundwater, construction conditions and structural load cases.

This guide explains the overall engineering workflow. The worked formula and arithmetic are provided on the separate Shallow Foundation Bearing Capacity Calculation page.

What bearing capacity means

Foundation pressure changes the stress state in the soil or rock below and beside the footing. If the available shear resistance is exceeded, the foundation may experience a general, local or punching-type failure. The governing mechanism depends on ground strength, density or consistency, footing size, embedment, load direction and stratigraphy.

Bearing capacity should not be confused with settlement performance. A footing may have adequate resistance against shear failure but still settle or rotate beyond the project's serviceability requirements.

Information required before calculation

A defensible assessment normally requires:

• Foundation type, width, length, founding level and base condition
• Vertical, horizontal and moment actions for the relevant load cases
• Ground profile and the thickness of each controlling layer
• Effective-stress or total-stress strength parameters appropriate to the design condition
• Groundwater level, possible variation and construction-stage water conditions
• Soil or rock unit weights and any surcharge near the footing
• Excavation disturbance, fill placement and founding-surface preparation
• Project design basis, consequence category and applicable standards

Parameters should be traceable to the site investigation, laboratory or field testing, engineering interpretation and the selected design method.

Drained and undrained assessment

Short-term loading in saturated fine-grained soil may be assessed using an undrained total-stress model. Long-term behaviour commonly requires an effective-stress model using effective cohesion, friction angle and pore-water conditions. These are different calculation branches and should not be mixed without a documented engineering basis.

Groundwater and layered ground

Groundwater can reduce effective stress and change the unit weight used in parts of the bearing-capacity model. A water table within or below the influence zone may affect surcharge and soil-weight contributions differently.

Where a weaker or more compressible layer lies below the founding stratum, a single homogeneous-soil equation may not represent the critical mechanism. Layered-ground failure, punching, settlement and excavation stability may require separate analysis.

Eccentric and inclined loading

Moments and horizontal actions can reduce the effective foundation area and alter the failure mechanism. Contact pressure should be assessed before selecting the bearing-capacity calculation dimensions.

• Footing Pressure and Eccentricity Calculations
• Shallow Foundation Bearing Capacity Calculation

Checks that remain separate

A bearing-capacity result does not replace checks for:

• Immediate and consolidation settlement
• Differential movement and footing rotation
• Sliding, uplift and overturning
• Global or excavation stability
• Structural capacity of the footing
• Construction verification and founding-level inspection

Calculation resources

• Shallow Foundation Bearing Capacity Calculation
• Immediate Settlement of Shallow Foundations
• Consolidation Settlement Calculation
• Footing Pressure and Eccentricity Calculations

Engineering note

There is no universal allowable bearing pressure, factor of safety or resistance factor. The design method, actions, parameter selection and acceptance criteria must be established by the responsible engineer for the project.