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 Strand7, 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