Allowable Bearing Pressure
Allowable Bearing Pressure
(OP)
Is there an acceptable correlation (i.e. tables, equations, etc.) between compaction test results and allowable bearing pressure? Specifically, I have a client who is planning on placing a CMU wall, single-story, slab on-grade building on about 15 feet of compacted fill. The fill, which consists of sandy lean clay (CL), has a low to medium plasticity and all compacted lifts (about 10" loose lifts) exceeded 95% of the stand. proctor (D-698).
Also, no test borings (or test pits) have been competed previously in this area.
Also, no test borings (or test pits) have been competed previously in this area.





RE: Allowable Bearing Pressure
RE: Allowable Bearing Pressure
RE: Allowable Bearing Pressure
Bearing capacity depends on several variables and soil density is only one. Overburden confinement has a much greater effect on bearing capacity than compaction; however, as density increases, so does the overburden efficiency, though not greatly.
The appropriate test for bearing capacity is the plate load test.
RE: Allowable Bearing Pressure
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RE: Allowable Bearing Pressure
The problem with plate load tests it that the "zone of influence" for the plate is typically not as deep as the foundation, and the results could be misleading. One thing you could do is monitor the settlement over a period of time at some set points to see what is going on with the fill. Having said all that, considering the type of fill and its compaction along with the relatively light structure, this discussion is probably academic unless the fill was placed over some soft compressible soils.
RE: Allowable Bearing Pressure
Focht3 has extensive experience with clay and foundations. Hopefully he can provide insight to this.
RE: Allowable Bearing Pressure
RE: Allowable Bearing Pressure
Sorry everyone,
What occurred wrt the LRFD question, I missed all the responses and now the thread was removed. What happened?
Regards
VOD
RE: Allowable Bearing Pressure
RE: Allowable Bearing Pressure
With 15 feet of fill - compacted or not - settlement is definitely the principal issue. That's 180 inches; at 2% shrinkage (typical for lean clays) you will get about 3½ inches of settlement due to fill shrinkage alone.
And we haven't even discussed elastic and consolidation settlement, or bearing capacity for that matter.
Soil borings are clearly required, as well as a statistical evaluation of the compaction testing of the fill. The fill was tested at every lift, right? If not, the fill may not be usable...
Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See FAQ158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"