Special Topics: Modulus of Subgrade Reaction

Description

The modulus of subgrade reaction, , is the relationship between soil pressure,, and the resulting deflection, . That is,

It is widely used in the analysis of continuous footings, mats, and different types of pilings.

In Straus7, the modulus of subgrade reaction can be used directly in the definition of Brick Face Support, Plate Face Support and Plate Edge Support attributes as these attributes are area based. The units of for these attributes is therefore Pressure/Deflection (e.g., N/m2/m). When used for beam elements, the beam width needs to be taken into account to convert into a Force/Length/Deflection quantity (e.g., N/m/m) .

Typical values of the modulus of subgrade reaction (to be used as a guide) are extracted from Reference [1] and listed below where is the allowable bearing pressure. A wide range of values is given in each case since for most footing/soil configurations, the value of varies with the size of the footing. Reference [1] offers suggestions for calculating as a function of (modulus of elasticity) and (Poisson's ratio) of the soil.

Soil
Loose sand 30 - 100 4 800 - 16 000
Medium dense sand 60 - 500 9 600 - 80 000
Dense sand 400 - 800 64 000 - 128 000
Clayey medium dense sand 200 - 500 32 000 - 80 000
Silty medium dense sand 150 - 300 24 000 - 48 000
Clayey soil:    
75 - 150 12 000 - 24 000
150 - 300 24 000 - 48 000
> 300 > 48 000

[1] Bowles, J.E. 1997, Foundation analysis and design, 5th edn, McGraw-Hill Companies, Inc.

See Also