## Modulus of Subgrade Reaction

## Modulus of Subgrade Reaction

(OP)

Can anyone suggest ways of accurately estimating the Modulus of Subgrade Reaction for a soil. Available parameters:

SPT N values, Moisture, Unconfined Compressive Strength & Angle of Internal Friction.

SPT N values, Moisture, Unconfined Compressive Strength & Angle of Internal Friction.

## RE: Modulus of Subgrade Reaction

## RE: Modulus of Subgrade Reaction

## RE: Modulus of Subgrade Reaction

I agree with what you say.."accurately estimating" is a bit of a loose term so to speak and hence my posting. The SE I am working with insists that I do that and I am not sure how to do that!

I am referring to Bowles it has some equations and stuff but to estimate that for 50 Borings with 10 soil layers in each seems like its going to take me a week to do all that!

## RE: Modulus of Subgrade Reaction

It all of a sudden seems like I'm writing into these dirt forums a little too much--so this will be my last one.

I read a soils report in the last couple months. Where the soils engineer gave the modulus and stated it was for a 1 ft x 1 ft plate and that the value given should be adjusted for the actual footing size. No guidance as to how it should be adjusted was further given.

## RE: Modulus of Subgrade Reaction

I am not sure about what you designed for but this foundation analysis is for a Bridge Abutment 150 feet wide passing over a six-lane highway. They are going to use micropiles and H-piles combination. I am not gonna get off as easy as your soils engr.

## RE: Modulus of Subgrade Reaction

Check out the NAVFAC manual for both.

## RE: Modulus of Subgrade Reaction

Which NAVFAC manual are you talking about? I have four or five of them.

## RE: Modulus of Subgrade Reaction

printed sometime around '50

best tincan

## RE: Modulus of Subgrade Reaction

Your SE is probably looking at lateral deflections of abutment piles. As Eric1037 sugests you may require lateral subgrade modulus which can be obtained by multiplying the values obtained for a 1ft square plate by 2. However, I do not want you to take values without understanding their limitations. As such you may wish to do some further reading. Foundation Analysis by RF Scott is a text which you should look at as he discusses this topic.

I presume that these modulus values are required for a computer program that Structural Engineers like to use for these problems as you can model utilizing a large number of springs. I cannot remember the name of the program. However there are other methods as well.

Just a suggestion before you go picking numbers why don't you discuss with the SE what he is aiming at, find out how deep the piles are to be embedded and after that examine the soil characteristics and use a few ounces of judgement in deciding the information to be provided. Discuss same with your SE and come to some agreement. This way you avoid giving numbers that may be inappropriate and giving numbers just for numbers sake. Too often we are controlled by computer programs without fully understanding the limitations. As well try out some simple approaches while he tries out his approach.

Regards

## RE: Modulus of Subgrade Reaction

I use the NAVFAC Design Manual 7.01 and 7.02. See pg. 7.2-235 for lateral subgrade in 7.02. The modulus of subgrade reaction is in 7.01 chapter 5 pg. 7.1-219.

## RE: Modulus of Subgrade Reaction

Structural engineers like it because it is simple. I try and keep it simple. The subgrade modulus is frequently specified in terms of pounds per cubic inch or kips per cubic inch. For a footing on the ground (say on sand) we frequently quote an allowable bearing pressure as pounds per square foot for one inch of settlement. This is essentially a subgrade modulus that considers the size and shape of the footing. A one foot square footing on sand will have a different allowable bearing pressure than a 10 foot square footing for the same 1 inch of settlement.

I would be interested in feedback on this simplistic interpretation.

## RE: Modulus of Subgrade Reaction

## RE: Modulus of Subgrade Reaction

## RE: Modulus of Subgrade Reaction

## RE: Modulus of Subgrade Reaction