Field testing to verify allowable design bearing pressure
Field testing to verify allowable design bearing pressure
(OP)
How do DCP test results correlate to verifing allowable design bearing pressure? I know you can correlate DCP blows to a N-value which is how the orginal alowable bearing pressure is based upon along with other soil properties (phi angle(friction angle), coheision value, unit weight, etc). I have heard that a DCP is 2.5 to 3 times a a N-value. Are there any papers, publications, or standards that better descibe how to verify allowable bearing pressure in both sands and clays with DCP or hand penetrometer tests? My geotech textbook only explains how to calculate bearing capacity using terzaghi and other methods to check for settlement and bearing capacity with soil boring data but there no explaination on how to verify that allowable bearing pressure has been achieved in the field during the actual construction process.





RE: Field testing to verify allowable design bearing pressure
Good luck.
f-d
¡papá gordo ain’t no madre flaca!
RE: Field testing to verify allowable design bearing pressure
RE: Field testing to verify allowable design bearing pressure
Depending on the sensitivity and importance of the structure, full-scale footing load tests may be performed using pile testing equipment to determine the load-deformation response of the foundation media.
As fatdad states, you need to take your verification through the influence zone of the foundation.
Jeff
RE: Field testing to verify allowable design bearing pressure
Full "load tests" would not be performed except for important structures (and this includes settlement sensitive ones) - they are costly AND one wouldn't be flatulently considering the use of a DCP in such cases. Full "load tests" would be the most positive way to go in sands or relatively free draining soils but I would be leary in cohesive due to the slow porewater pressure response below large load tests - and don't look at "standard" plate load tests as being anywhere close to an equivalent.
You might do a search on the net for something - I recall seeing some 'hits' on using a DCP for residential (and light commercial) structures.
RE: Field testing to verify allowable design bearing pressure
RE: Field testing to verify allowable design bearing pressure
Also, it should be used with much caution, being sensitive to lateral friction with the borehole.
In sandy soils, torque measurements are taken to check the presence of any spurious situations.
In clayey soils, results are much more iffy.
RE: Field testing to verify allowable design bearing pressure
RE: Field testing to verify allowable design bearing pressure
I really hate to think that ASTM will get to far into this as it has more to do with the geology and the engineering properties at depth than just running a test on the subgrade.
f-d
¡papá gordo ain’t no madre flaca!
RE: Field testing to verify allowable design bearing pressure
RE: Field testing to verify allowable design bearing pressure
Some things urk me - ha.
f-d
¡papá gordo ain’t no madre flaca!
RE: Field testing to verify allowable design bearing pressure
"New Soil Compaction Verification at Shallow Depths Using the 5-lb Dynamic Cone PENETROMETER--This test method covers the procedure for the determination of the number of blows required for a dynamic cone PENETROMETER with a 5-lb (2.3-Kg) drop weight falling 20 inches (508 mm) to penetrate a certain depth in undisturbed soil and/or compacted backfill. This test method can be used for the determination of compaction efforts of soils, subgrades, and granular base materials at shallow depths."
while i have used dcp to very generally describe the inferred compaction (i.e. "poorly compacted") of shallow fill, i'm interested to see how astm prescribes such a method and quantitatively describes the compaction when the test can give such widely varying results depending on the material or things contained therein.
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RE: Field testing to verify allowable design bearing pressure
RE: Field testing to verify allowable design bearing pressure
depending on how it's written, i could see a spec like that being used as a scapegoat for shotty engineering. say you've got a shallow sandy silt soil fill that has #57 stone scattered throughout. Shotty Engineering Inc runs dcp and get 16 bpi and conclude that the fill is compacted to 98% modified Proctor compaction. then whatever the fill is supporting then settled 3 inches. and as it turns out, the fill was backdumped and not well compacted but got high blowcounts because of the aggregate. they could say, "we followed astm and industry standards therefore we exercised a reasonable standard of care."
i tend to agree that having an astm test method that a monkey could run does not substitute true engineering.
RE: Field testing to verify allowable design bearing pressure
I can see it now. . . .
f-d
¡papá gordo ain’t no madre flaca!
RE: Field testing to verify allowable design bearing pressure
RE: Field testing to verify allowable design bearing pressure
RE: Field testing to verify allowable design bearing pressure
Does any one know where I could get a copy of this I found the Symposium on Engineering Geology & Soils Engineering web site but this volume is out of print.
RE: Field testing to verify allowable design bearing pressure
I wanted to echo the collective sentiments of others about standards. No matter how good the intentions are, standards, and the use of them, can range from "decent guidelines" to "things that should be obvious to even the most casual observer" to "worthless" all the way to "downright dangerous." Good judgement, while carefully considering all of the neat numbers you can get with testing, needs to prevail.
RE: Field testing to verify allowable design bearing pressure
Anyway, to answer your original question, check out George F. Sowers and Charles S. Hodges, "Dynamic Cone for Shallow In-Situ Penetration Testing" Vane Shear and Cone Penetration Resistance Testing of In-Situ Soils, ASTM STP 399, Am. Soc. Testing Mats., 1966, p. 29. Please be aware, as stated in the abstract, that "...the penetrometer has been found useful in the inspection of footing foundations and for light field exploration where the standard penetration range of limits is generally know. The test data show that it is capable of approximating the standard penetration resistance for the virgin soils of the southeastern U.S." I hope this gives some direction. Best regards.
RE: Field testing to verify allowable design bearing pressure