In geotechnical engineering, soil subgrade modulus is a critical parameter in calculating the deformation capability and soil settlement capability. The soil subgrade modulus formula is used to determine soil stiffness for foundation or footing.
Soil subgrade modulus calculation formula
Modulus of subgrade reaction of soil (𝑘):
k= qu/Δ
Where:
- = ultimate bearing capacity of the soil (load per unit area)
- Δ = deflection under the applied load
Common Units for modulus of subgrade reaction
Metric System
- : kN/m² or kPa (kilonewtons per square meter)
- Δ: mm (millimeters)
- k: kN/m³ (kilonewtons per cubic meter)
Formula: k (kN/m³)=qu (kN/m²)/
Imperial System
- : psf (pounds per square foot)
- : in (inches)
- : pci (pounds per cubic inch)
Formula: k (pci)=qu (psf)/
Modulus of subgrade calculation Excel sheet
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