circular plate for determining the load-bearing capacity

[Chema]

Hi! I'm searching information about settlements of load plate test and real shallow foundation relationship. I have found the equation Terzaghi and Peck (1.967) but I think this equation isn't accurate. I haven't found other equation.
Anybody can help me?

 

[BigH]

Now, why would you think Terzaghi and Peck would not, as leading founders of the geotechnical profession, offer "accurate" discourse on the plate load test?? Give some reasons why. 'ell, these two cats helped invent (with a few others) our field!!!

 

[Ron]

Plate load tests were developed as practical, "real" condition tests because the generalized tables developed from theory were not showing to be accurate.

Most of the leaders of Geotech profession (Terzaghi, Peck, Sowers, et al) were quite comfortable with the concept and result of plate load tests (yes, you have to understand their limitations and work within them!).

It is the closest thing you'll get to a full scale foundation test.

 

[Focht3]

Hmmm,

PLTs aren't the closest thing to a full scale load test - I've run a few of full scale load tests before on partially instrumented drilled piers, and loaded them to plunging failure. (Up to 24 inch diameter, 80 ft embedded length - pushed over 7 inches into the ground...) You can get close to this on other foundation types by instrumenting structures for load, and getting a series of third order level surveys of the tops of the foundations during key points during and after construction. ( + 0.001 foot with a closure error of less than 0.004 foot.) Clients will pay for it when they see a benefit.

Frankly, we have enough fancy analytical methods and computer simulations - what we need is more field performance data.

P.S. I "borrowed" the immediately preceding sentence from Ralph Peck; he said it about the time I was born!

 

[BigH]

I agree with Focht3 about PLTs. I've mentioned my nagging questions about them previously in other threads. On my current overseas road assignment, the designer wanted to use a plate load test (say 600mm dia plate) at the base of where a retaining wall was to be placed. I balked and forced a boring to be done (he wanted to do this in lieu of a boring). We found 1.5m of stiff clayey fill over desiccated crust about 1.5m thick (stiff to upper firm) - then found 6m of very soft clay with organics. Now, running a PLT with, say 2m of stiff to firm clays would have given a "nice" result but the full scale structure would have behaved absolutely miserably. They are good, perhaps for cohesionless soils where you "know" that the relative density is increasing - but they may be fraught with many dangers if you do not appreciate their limitations - as Ron rightly pointed out on that one. Too many might not realize the limitations of such tests - especially some who have never really gotten dirty.

 

[Chema]

I agree with bigh and focht3 about PLT. But I have seen other geotechnical reports, where the qu is divide by a SF. I think that isn't correct operation. I think the equation Terzaghi and Peck (1.967), is based on low number datas. So, I ask, Is there other method more confirmed? Thanks

Note: PLT = point load test

 

[Ron]

A few points of clarification, though it would appear that we are all saying similar things, just in a different manner....

The plate load test has, essentially, two functions:
1) For help in assessing the bearing capacity at the surface or foundation bearing level
2) To assess the modulus of subgrade reaction for pavement applications

It is not a predictor of overall foundation performance, though it is a fair representation of a bearing condition at the location of the test, if the test is properly run. It isn't as easy to do correctly as it would first appear and certainly not as easy as the textbook schematics would imply! One must be careful about the interpretation of the data when considering settlement and geotech parameters other than bearing at that location. As BigH noted, the plate load test should not be substituted for boring data....they are complementary processes. Further, in highly stratified near-surface soils, bearing capacity and settlement can be more closely related than in conditions where the soil is more consistent through the 2B range(or deeper in some cases).

 

[Chema]

Thanks Ron, but the problem, I know the limitations about PLT and I know don't exist magic equations but I want know the different equations exist. For example, the SPT, it correlation is very complicate but there are numerous equations of diferents autors. Each Geotechnical Engineer uses an equation of SPT apropiate a his project or conditions.
I want different correlations equations but I can decide. Do you understand me??

Thank everybody