What tests to run on a shelby tube
What tests to run on a shelby tube
(OP)
I am working on a site that has approximately 10 feet of fill that is loose to medium dense sand (N ~ 3-10) on top of approximately 10 feet of loose clay (N ~ 1-5) on top of some stiff clay till (N > 10). From historic photos, it appears that the site was originally a wetland that was filled in for a parking lot. We are now looking at putting up a senior living facility and a medical building. We drilled 15 borings and took shelby tubes in the two layers of clay. I am wondering what are the best tests to run on these shelby tubes? I have never collected shelby tubes and do not have a lot of experience in this area.
I spoke with the lab and they said I could run either a UU test ($160) or a CU test ($500). They also said that I would need to tell them the confining pressure for running the CU test?? They also said I could run an Unconfined Compression test ($72).
So, what tests do you recommend and what information will be given to me with the test results. Any other recommendations regarding the foundation for the buildings? Piles, geopiers, excavate??? Thanks.
I spoke with the lab and they said I could run either a UU test ($160) or a CU test ($500). They also said that I would need to tell them the confining pressure for running the CU test?? They also said I could run an Unconfined Compression test ($72).
So, what tests do you recommend and what information will be given to me with the test results. Any other recommendations regarding the foundation for the buildings? Piles, geopiers, excavate??? Thanks.





RE: What tests to run on a shelby tube
How many oedometers that actually is depends on the size of the site and how consistent the material is from place to place. You need them in both clay materials. If you put the buildings (presumably pretty light) on shallow foundations on the sand, I think you could probably get adequate bearing capacity from strip or spread footings, but potential for differential settlement is likely to control the design. Even if you put in some sort of deep foundation or excavate down to the stiffer clay, there is a good chance that settlement will govern your design, with bearing being secondary. N>10 is not high enough that I would write off differential settlement without testing. It would have to be N>>10.
If you think you might be excavating, you would want undrained shear strength for the materials exposed, for stability of cut slopes. I prefer UU over unconfined because it helps to reduce the effect of sample disturbance. The oedometer tests can give you a reasonable estimate of undrained shear strength using correlations with material type and preconsolidation stress. (See C.C. Ladd's SHANSEP papers, which your geotech should at least know of.) If you think you might use piles bearing in the lower clay, then you might want CU with pore pressure measurements to get the effective stress parameters for long-term (drained) strength.
Does that help you, hydroponder?
DRG
RE: What tests to run on a shelby tube
RE: What tests to run on a shelby tube
RE: What tests to run on a shelby tube
The real problematic soil is the 3m (oops, 10 ft) of very soft to soft clay). If you can densify the sand fill to say average N value of 20, you might be able to ensure that the zone of influence of your building foundation (presuming 2 storey or less) pressure distribution wholly in the sand. This would not "load" the clay unless you are also regrading the site and placing additional fill. Lots of variables on a site where you have shallow fill over shallow soft clay. In India, we used wick drains and built a 10 m high retaining wall on 6 m of similar clay. It worked - but we did have 1000mm of settlement!
RE: What tests to run on a shelby tube
RE: What tests to run on a shelby tube
RE: What tests to run on a shelby tube
I've had to use this over old dumps, peat filled river beds, etc. The main drawback seems that the utilities are either under the slab or within the "cavities" between the "T" sections of the slabs and future access to them is practically impossible. We've put 5 story apartments on these situations and no problems with depth of "T" on the order of 4 feet.
For the structural engineers we tell them to design the slab so that any area "X" x "X' has no support under it. For single story buildings we usually make "X" = 10 ft. for lack of a better guide.
RE: What tests to run on a shelby tube