## settlement from plate load test and real footing

## settlement from plate load test and real footing

(OP)

Hi all, can anyone help to solve my problem? Normally, Plate load test is used to verify the site soil bearing capacity. but normally the settlement is quite small. (say 5mm of settlement while applied pressure of 350 kpa, which means, if reach a settlement of 25mm, the pressure can be 1000 kpa+, not really tally with the calculation). I also heard while the footing size is bigger, applying same pressure on top, the real settlement will be bigger. Can anyone share with me the relevant reference book? Many thanks.

## RE: settlement from plate load test and real footing

Soil mechanics in engineering practice by Karl Terzaghi.

Fundamentals of Ground Engineering by John Atkinson.

A short course in Foundation Engineering by Simons & Menzies.

## RE: settlement from plate load test and real footing

## RE: settlement from plate load test and real footing

## RE: settlement from plate load test and real footing

## RE: settlement from plate load test and real footing

f-d

ípapß gordo ainÆt no madre flaca!

## RE: settlement from plate load test and real footing

thanks, i have that book, may i know which chapter has the answer? I'd like to have a study.

## RE: settlement from plate load test and real footing

## RE: settlement from plate load test and real footing

## RE: settlement from plate load test and real footing

## RE: settlement from plate load test and real footing

1'-0" x 1'-0" footprint tells you almost nothing about the behavior of a 5'-0" x 5'-0" footprint.

Lab testing and simple hand calcs are the main tools for evaluating settlement and bearing capacity.

## RE: settlement from plate load test and real footing

I agree that the results can be misleading in stratified soils, but if you know that the soil is consistent within the depth of influence, you can factor up the results and make use of them. Some soils and highly weathered rock are not suited to sampling and lab testing, and field tests must be resorted to.

If you don't know the subsurface conditions to the depth of influence, you need to explore.

## RE: settlement from plate load test and real footing

I suppose that if your soil profile is truly a uniform, isotropic, elastic, saturated, homogeneous soil with the same composition beginning at the ground surface and extending to the depth of the zone of influence of the full size footing, it might give you a good idea. But soil is not uniform, isotropic, elastic, or homogenous.

And, the big one, how often do you have the water table at ground level? More likely, the water table is at some depth and all of the soil in the zone of influence of the plate load test is under the influence of matric suction and other fun things about partially saturated soil mechanics that make the results of the test, in essence, totally meaningless when compared to a real footing.

## RE: settlement from plate load test and real footing

## RE: settlement from plate load test and real footing

thanks for your advice and reply.

I check with section 4.12, it is about how to determine the bearing capacity from field load tests (say plate load test). And some formula mentioned,Qult = Qplate (Bfoundation / Bplate). assume Bfoundation / Bplate = 3 (same to the design FOS) Qall = Qplate which base on most of my received test report, it can be ....say 300 kPa or even much more, as the settlement at that pressure is only 5mm--10mm, not 25mm. (Assume it is correct, i see the textbook also mentioned some limitation for this method use, but for certain case, seems like it still can be used). This allowable pressure obtained is much bigger than what calculated, and in my country, soil is not so good. (I know in US, some part of the soil is really good), so i don't really believe this result. Any other reference or correction method that i can refer to?

and my another question which this section 4.12 does not give me the answer is..... if the applied pressure for the plate load test is 300kPa and the obtained settlement is 5mm. what will be the expected soil settlement if the footing size is 1.5m x1.5m ? any reference can refer to?

many thanks to all.

## RE: settlement from plate load test and real footing

## RE: settlement from plate load test and real footing

The pitfalls are numerous and serious enough that I would not recommend attempting foundation design from plate load tests unless (1)the soil is confirmed to be uniform to at least 2 times the width of the proposed footing and (2) You have a thorough understanding of the principles of both ultimate bearing capacity and settlement.

## RE: settlement from plate load test and real footing

OK，thanks for your advice.

may i know, what is the method you will use to verify the site soil bearing capacity after compaction / construction? Say base on the soil report / SPT value or Cu value, you use allowable soil bearing capacity of 100kpa , and on site did some compaction, etc. how do you determine the site actual soil bearing capacity?

thanks

## RE: settlement from plate load test and real footing

We would evaluate the native soils using unconfined strength for clays and SPT for sands. If the native soil is significantly weaker than the fill, we might select the fill thickness to limit the pressure at the top of the native soil to its allowable bearing pressure, or reduce the design footing bearing pressure if necessary.

For heavy loads or unfamiliar soils, we might resort to unconfined or triaxial tests on compacted fill specimens and consolidation tests on compressible clays. We might estimate elastic moduli of both fill and native soils from published correlations to calculate settlements. If compressible soils existed at depth, we would adjust the combination of bearing pressure and structural fill thickness to avoid stressing the soft soils above the preconsolidation pressure. If that was not feasible, we might preload the building site or resort to deep foundations.

## RE: settlement from plate load test and real footing

many thanks for your reply.

so if my understanding is not wrong, you will do a lab test to get the soil density after compression. say the clay layer standard density is 18 kn/m3, if you test can reach a density of 18/0.95 (or 18*0.95, sorry which one is right?) , it assumed that the soil is compacted to the design requirement, am i right?

thanks again.