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Soil sub-grade modulus

Soil sub-grade modulus

Soil sub-grade modulus

I want to know the correct way to calculate the Soil sub-grade modulus, is the correct value is Kv = P/D where P is the allowable pressure and D is the corresponding allowable settlement or P is the ultimate pressure and D is the corresponding ultimate settlement?
Since i found in many soil reports that the Kv= FS*(B.C)/D where D is the allowable settlement

RE: Soil sub-grade modulus

The correct way is what you have said. Pressure divided by settlement.

Is Kv= FS*(B.C)/ D = Bearing capacity X factor of safety ?

I don’t think that is correct as it is your ultimate capacity divided by settlement. This will give you a higher modulus of subgrade reaction. It should be your bearing pressure that achieves your allowable settlement, not ultimate capacity.

RE: Soil sub-grade modulus

obtain a soaked CBR value for a sample compacted to the target density and relate the CBR to subgrade modulus.


ípapß gordo ainÆt no madre flaca!

RE: Soil sub-grade modulus

I have used in the past Kv = FS*(B.C)/D.

Also there are many correlations depending on the type of soil and consistency, there are ranges of K values. See bowles or Coduto.

RE: Soil sub-grade modulus

Ihab -

Soil subgrade modulus is a model element. Soil subgrade modulus is not a characteristic of the soil - that is the first concept to understand, and I think you do.

Then, the model element (k) that you use should represent the actual load (contact pressure) divided the expected deflection under that load. It is shape and load dependent, as well as dependent on the subsurface conditions. You want the value to as closely as possible model what will actually happen under the load.

Soil subgrade modulus can also vary across a large loaded area - like a mat foundation - where you shouldn't use a uniform value. If you put a uniform load on a mat on uniform soil conditions, the mat usually dishes (plastic soils). Therefore, even though all the conditions are the same (except stresses), the model elements (k) will vary across the mat to correctly model the dishing.

Hope this helps.

RE: Soil sub-grade modulus

Hi ,

I would like to know "Is there any correlation to calculate Safe Bearing Capacity from Sub grade modulus?"

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