plate bearing tests - can you derive soil density and/or friction angles from these? 1

[ac4u2nv]

I have some plate bearing test results giving the Ult bearing capacity for the subgrade which a piling platform will be formed upon.
How do I equate these values back to giving me a bulk unit weight and a friction angle so I can design the piling platform?

Could i do a cross comparison calc and back fit using Terzaghi or Meyerhof bearing equations? I’m only after an approximation
So we know the Qult, diameter of circular plate and we know this is 6F2 material on top of made ground. So if I fix the bulk unit weight at say 20kn/m3 and then alter the friction angle to achieve a similar Qult as the Plate Bearing Tests?

Would this work and is comparable?

 

[GeoEnvGuy]

I do not know of any correlation from PMT to unit weight.

The correlation mentioned for PMT to friction angle references the Hughes et al 1977 Pressuremeter test in sands article.

 

[BigH]

It amazes me that so many still do plate load tests where in situations that are, at least in my view, not applicable. The tests described here are for a piling platform. What is the size of the platform? What is the effective depth to which the plate load test is applicable? The latter - for no more than 1000 mm but typically 600 mm (2 x plate diamter, typically 300 mm). The former, being many metres in size - 20 to 30? or more? - affects the ground to depths of many many metres. Is the plate load test applicable? I think not. What if 2-1/2 m down, the soil became a soft clay - and not the surficial desiccated crust of the clay? What if? . . . something I was always asked when trying to explain things like "What is the probability of the 200 year earthquake happening in the 2 month construction window?" - my mentor's response? "What if?"

Case in point. In India, the Calcutta clay plains, the stratigraphy consists of about 6 m of very soft clay (N = 0 to 2, Su = 15 to 20 kPa) overlying firm (medium stiff) to stiff clay. As a general rule, ground improvmenet - pvd with stage loading, were needed to construct the MSE bridge approach embankments. At one location where it was a "built up" ground, a structural engineer said "No need. We'll do a plate load test." He did the test and said that the site was good for 350 kPa bearing pressure so no problem building the MSE wall "full height". Yours truly fought to do the ground improvement; and won. The first 4 m layer of the MSE embankment was placed and the embankment settled 400 mm. Did the plate load test show this? No. The plate load test was done in a 2 m thick built up ground and only tested the built up ground - not the soil "at depth" which would be stressed by the embankment. So my word of advice - unless for pavement design (thin layers of subbase/base) - do not rely on plate load tests except in very well defined situations.