Minimum Depth of Foundation calculator

 

Minimum Depth of Foundation

Minimum Depth of Foundation calculator

The minimum depth of foundation is the shallowest level below the ground surface at which a building's foundation must be laid to ensure stability and safety. This depth is essential to:

• Avoid surface disturbances caused by weather, moisture changes, frost, or soil shrinkage/swelling.

• Reach soil with adequate bearing capacity to safely support the building load.

• Prevent uneven settlement and structural damage.

Minimum Depth Guidance (IS: 1904, Indian Standard)

• General residential buildings: minimum 0.5 meters (50 cm) below natural ground level.

• Sandy soils: minimum 0.8 to 1.0 meters.

• Clayey soils: minimum 0.9 to 1.6 meters.

• Rocky or hard soils: minimum 0.05 to 0.5 meters.

Factors Affecting Foundation Depth

• Soil type and bearing capacity

• Load imposed by the structure

• Water table level

• Climatic conditions (especially frost)

• Local ground conditions and prior site history

Rankine’s Formula for More Precise Calculation

For a site-specific calculation, Rankine's formula can be applied:

$$$$Df=qγ×(1−sin⁡ϕ1+sin⁡ϕ)2

Where:

• $D_f$ = minimum foundation depth (meters)

• $q$ = gross bearing capacity of soil (kN/m²)

• $\gamma$ = unit weight (density) of soil (kN/m³)

• $\varphi$ = angle of internal friction (angle of repose) of soil (degrees)

This formula accounts for soil strength and density parameters to give a calculated minimum depth.

Minimum Foundation Depth Calculator

Bearing Capacity, q (kN/m²): Soil Unit Weight, γ (kN/m³): Angle of Repose, φ (degrees):

IS:1904 Quick Guide:
Residential/General: ≥ 0.5 m | Sand: 0.8–1.0 m | Clay: 0.9–1.6 m | Hard Rock: 0.05–0.5 m