Foundation subgrade modulus

[qcjr]

Hello all,

This is a question about using springs to model a soil foundation, in a structural design software. The software uses "kN/mm" as an input value for the spring supports.

I would like to know if anyone here, either by experience or with a reference, can guide me to find some typical values to use as an input for the software? I have a doubtful source with values in "MPa/m" (which could be converted to kN/mm by using the tributary area of the support) but I'd rather use a more reliable source.

(I say the source is doubtful because it only gives me a range, i.e. "between 13.5 MPa/m for weak support, to over 270 MPa/m for strong support").

 

[yanghtou]

Hi qcjr,
Plate bearing test at level of considering pressure is the most relevant tool in order to determine this parameter. It's quite an empirically based number.

Best wishes

 

[hughits]

Most of the typical values found in many references are normally given in ranges simplely because they are typical values in my opinion.
What valve you want use within the range is solely up to you (of course if you want to use the typical values). I would use a value that will give me a bit conservative design.
Try some references such as Bowles, Das, Day, etc. They normally give you those ranges.

 

[BigH]

One other thing you might try is to input a range of values into your programme and determine the "sensitivity" of the inputted values. Develop a curve and then, by hook or crook, check out what seems to be a reasonable value - I would do this with slope stability problems - plotting Su vs FS - then I could see the 'range' of probably FS for the likely Su (plus and minus a bit). Suggest you consult Tomlinson - I don't have it handy - but he is a real engineer and his book on Foundation Design is excellent.

 

[msucog]

i believe some values are available in navfac (ufc soil mechanics 220-10n i think)

 

[fattdad]

Make sure you also know the bearing pressure for overall soil support. Just using a spring constant (i.e., as mobilized by the soils within 10 to 12 inches below the foundation is only half the story.

f-d

¡papá gordo ain’t no madre flaca!

 

[qcjr]

Ok, thanks for the input, guys. We just bought the Canadian Foundation Engineering Manual, which gives some estimated values for the subgrade reaction modulus.