Plate Bearing Test

[jjsim]

Hi,

Plate bearing test applies load to the ground via a 300mm x 300mm steel plate. From the test, the load vs settlement and time vs settlement plots are given.

From the plate bearing test, how to get:

1. Ultimate bearing capacity for an actual footing with a size much bigger than the steel plate ?

2. What is the settlement of the actual footing under service load?

3. Any difference between clay and sand ?

Thanks

 

[ATSE]

I assume you are referring to ASTM D1194.
To your question, you can't extrapolate your load test data too far beyond your test parameters. Don't try to use results from 1ft x 1ft on anything bigger than a 3 ft x 3 ft spread footing. For a 1ft x 1ft plate, your results are valid for 2 - 3 feet depth. Not too meaningful for most multi-story structure foundations.
Settlement estimates should be based on sufficient subsurface exploration, lab tests, and geotechnical calculations.
In general, plate load test results are abused more often than not.

 

[oldestguy]

I have an old article on the subject concluding that the test is most suitable for sands, but no limit on the ratio of plate to footing size. He concludes the methods then for extrapolating to footings were UNSATISFACTORY. If you can find this article it may help. Some correlation to N values is presented also. I've used the test rarely and then applying a generous safety factor. I would run two tests on one location with significantly different plate sizes to assist in the extrapolation..

Parry, R.G. (1948) Geotechnique28, No 1. 107-118

 

[BigH]

There have been quite a few theeads on the use of plate load tests. Why not search on the site for them?

 

[Okiryu]

I think Bowles book has some information about plate bearing test and correlations to actual footing sizes. But as mentioned above you have to be careful when extrapolating the plate results to your actual footings... especially for clays.