Westergaard Slab on Grade Soil Bearing Pressure 1

[cap4000]

Can anyone verify with a 3,000 pound wheel load in the center of a 5 inch slab on grade that it transmits a maximum soil bearing pressure of just 150 psf. Westergaards formula is based on a radius of relative stiffness and a soil modulus. The soil k value I used was 300pci. Any tips will be greatly appreciated.

 

[Ron]

Running a quick elastic layer analysis, I get about 400 psf, considering a concrete modulus of 3,000 ksi and a soil modulus 20 ksi.

Your k value of 300 pci is relatively high. What type of subbase soil do you have?

 

[cap4000]

I know there is a difference between the two formulas. I used a conc. modulus of 3500 ksi and a 12 inch compacted gravel sub-base. The distance that the load transmits laterally on the soil varies from 2 to 3 times the radius of relative stiffness or around 3 to 4 feet. I think its similar to soils whereby the internal friction angle decays the original load. In this case its on the order of 10x to 20x less. Close enough.