Safe bearing capacity

[vinothsekar]

Hi,

I just want to know that "whether it is possible to calculate the safe bearing capacity from Modulus of subgrade in Plate load test?".

I have performed the plate load test, where i have concluded that the Ks value = 80 Mn/m2/m. Is there any empirical formula or correlation to calculate Safe Bearing Capacity?

 

[oldestguy]

To answer your ques ton. MAYBE. It may apply to a footing nearly th same size as your plate. For a larger footing some modification of the tests result is necessary to account not only for footing size but also soil properties with depth.

 

[vinothsekar]

Hi,

What kind of modification has to be done? Nowhere im finding the correlation or empirical formula.

 

[Mad Mike]

I don't think you will find any empirical correlation- your plate load test only produces results for a thin upper layer, in relation to the size of the plate testing apparatus.

To carry that information over to an estimate of bearing capacity, you need more information on the soil in the zone of influence beneath proposed footing- for example, if there is very soft compressible clay 4' down, this won't reflect on your plate test, but may significantly reduce the bearing capacity of a footing.

For general purposes, I would disregard the plate load test and run some penetrometer tests through the site profile.

All the best,
Mike

 

[vinothsekar]

Thanks Guys.

I would have performed plate load test by ASTM to analysis SBC value. Because DIN 18134 standard is only for Subgrade modulus and Settlement analysis.Also Canadian foundation manual say that half of your failure load from pressure vs settlement curve for Safe bearing capacity.

 

[maxim22]

The plate diameter is 600 mm, so reasonably close to a model small foundation.

The stress/strain curve shows small settlements <1mm at low stress, then very small settlements at >0.1MN/m2.

Is it possible that the steep curve is bedding in the test apparatus, then the second part of the curve is the ground response to load?

What is the ground model? Rock, clay or sand? Sketch out a cross section.

Check there is not a weak layer below the test by excavation.

 

[vinothsekar]

We have performed this test in Gabbon, Afria. its almost near to the Gabbon Port. overall soil strata at the shallow depth is Clay layer whereas Sandy soil at the top surface.

Vinothkumar S
Geotechnical Engineer

 

[Okiryu]

If I am understand this correctly, you have sandy soils at the surface following by clay soils?....if that is correct, what is the thickness of the sandy soil layer? What are your expected loads and footing sizes? As everybody is indicating above, depending on the thickness of the sandy soil layers, your plate bearing test will never see the response of the clay layer and if your footings are large, you will be missing very critical information...If your footings are expected to be large enough so their depth of influence for stresses will reach the clay layers, I just recommend to do some borings with undisturbed samples in the clay layer to test them to get modulus, Cc or shear strength parameters...then, you can just keep the plate bearing test results for rigid pavement design if you are planning for it at your site....