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modulus of sugrade reaction

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your explanation on the modulus of subrade reaction is quite helpful.  as i am a structural engineer, my knowledge in soil engineering is quite limited.  we basically depend on the geotechnical report when it comes to designing foundation.  and for the most part, the only useful information we get from the geotechnical report is the allowable soil bearing pressure.   and usually that is enough for us to design simple foundations such as isolated footings.  but now that i am faced with designing mat foundations, with the software we're using, the allowable soil bearing pressure that the geotechnical reports provide is no longer enough.  like you said, i think i should start requesting this info (the modulus) from the geotechnical people.

thank you once again.


seaint(--nospam--at) wrote:

>I can really give you an answer on your STAAD questions since it has been
>a while since I used it, but I can give a response on the modulus of
>subgrade reaction since it is not really STAAD related.
>The modulus of subgrade reaction really needs to come from a geotechnical
>engineer.  I am not aware of a way to determine it from "allowable"
>bearing pressure, but there are some geotechnical types on the list (they
>like to see how those of us on the darkside, aka structural engineering,
>live) who be able to offer some input.
>Basically, the modulus of subgrade reaction is the load required that must
>be applied to a plate of a set dimension (and stiff enough to behave as a
>"rigid" plate) to make that plate "settle" a some distance.  For
>example, take a plate that is 600mm diameter and apply some rather sizable
>load.  Measure how much it deflects/settles.  With that information (plate
>size, load, and deflection) the modulus can be determined with some
>adjustment for the flexibility of the plate.  Basically, the modulus is
>the pressure determine from taking the load divided by the plate area
>which is then divided by the deflection.  The resulting value is in the
>units of load/length^3.
>Therefore, I would suggest that you need to get some additional
>geotechnical information.
>Hope that helps.