Deep Foundation Cost Comparisons

[mad2323]

I have a site that will have 7-feet of dense gravel fill over 6-feet of soft sands (liquefiable) over native gravel at about 15-feet total. It may be hard to auger through the fill as it has cobbles. I'm considering micropiles, drilled shafts, geopiers, CFA piers, or whatever else would work best. I have had a hard time finding any comparative cost guidelines. For example, I suspect micropiles are more expensive than geopiers (in general) but just don't know. Does anybody have anything? Also, any thoughts on what concept would work best would be appreciated.

 

[ATSE]

A decent source for comparison can be found at:

http://geotechtools.org/

You will need to register, but that is relatively painless.
This site is geared toward transportation foundations / structures and imperfect (as everything is), but a good one-stop shop.

Geopiers (rammed aggregate piers) in the traditional form (drill and fill) would not be appropriate for a caving sand, as the process would require casing. Unfortunately, Geopier (the company) has used the term too broadly to apply to both drilled and vibro techniques, which are vastly different in equipment and applicability.
If you allow for predrilling the upper "crust" of dense native, you open up more options for either deep foundations or ground improvement. However, cobbles are always challenging.
What are your foundation loads and what is the totla expected depth of foundation / GI?

 

[mad2323]

ATSE thanks for that link it's helpful. I don't know yet what my foundation loads are but they won't be much maybe 20 kip column loads. The depth is 10-feet on average.

 

[ATSE]

20 kip column loads probably don't justify a deep foundation or ground improvement, even with liquefaction potential, provided you don't have liquefaction in the upper 6 ft.

 

[Okiryu]

I agree with ATSE, 20 kips (90 kN) column loads look low. For example, I have seen column loads of about 150 kips for residential buildings. Based on your penetration resistance from SPT, you may be able to check settlements due to liquefaction and see if shallow foundations are feasible. Just also wondering at what depth the water table is. BTW, I registered into geotechtools some years ago and it is a very nice reference for soil improvement techniques. I recommend it as well.