Foundation for a Vertical Turbine Can Pump

[rzrbk]

A foundation will be designed for a large new vertical turbine pump with a suction can. Given the size of the proposed pump, I suspect the foundation will take the form of a thick walled concrete cylinder approximately 6ft in diameter x 15ft deep in the ground. Since this is near the Gulf Coast, I believe the Civil Engineers' default will be to stick a bunch of piling under it.

I can't help but feel that a foundation this deep will be somewhat self-supporting, if looked at in the right way, so that installing piles at the bottom of a pit can be avoided.

Any suggestions for alternative type design methods to look at? I do not speak civil/geotechnical, so may not come up with the magic words to sway them from a default design path on my own. Not sure if this could be looked at as a drilled pier or other, or there is something specific that should be asked for in the geotechnical study (typically the soil studies will focus on the ground bearing for spread footers and allowable loads for depth x dia of piling).

If there is no feasible way around piling, that is OK too; thought I would check.

Thanks

 

[oldestguy]

Without specific soil data, why expect any useful suggestions?

 

[GeoPaveTraffic]

Hire a good geotechnical engineer to evaluate the site and your loads and give you recommendations.

Also, if you bid this work out among a bunch of engineers and take the low bid, then I expect you will get piles. If you select an engineer that you like working with and tell them you would like to avoid piles, then you have a chance.

Lastly, if you don't have an engineer that you like working with because you always bid the work out and always get what you think are conservative recommendations, then you getting both what you are paying for and what you deserve.

END OF SOAP BOX, for today at least.

Mike Lambert

 

[nackra]

Make sure that can is braced to keep the can plumb and to prevent floating or shifting when concrete is placed around the can.

 

[aeoliantexan]

I, too have often thought that the can and encasement could be constructed like a drilled pier. However, some of the factors that work against it include:
1. The suction line comes in pretty deep, requiring a sloped trench to intercept your pier hole.
2. The encasement often is used to support part of the floor load as well as the pump, so the load becomes substantial.
3. The designers want the can to be very plumb and to stay that way.
4. If there are several pumps, a lot of the building area gets excavated for the suction lines, and unless you can be very confident of the backfill quality, piles or piers will probably be used for the building frame.
5. The mechanical stuff is so expensive, and high performance for 50+ years is so important, that taking any risk to save a few bucks on the foundation doesn't make sense.

We often use a conservatively-designed footing to support the pump cans, because good soil or rock is often found at that depth. The can is carefully leveled on the footing, the RC encasement is formed, and the excavation, including the suction line trench, is partially or fully backfilled with flowable cementitious fill.

No complaints yet.

 

[JedClampett]

We use a concrete footing a little larger than the pump can. The bottom plate of the can is anchor bolted to the footing. Sometimes there's a line of pumps and we go with a strip footing. I'm not sure what the reason for a pile foundation is. The pump can, even with the water inside, weighs less than the soil it displaced. The motor and pump are pretty beefy, but not enough to require piles. The footing also allows the contractor to level the can and make it vertical.
A more real problem is what aeoliantexan mentions. We've had several cases of slabs settling due to poor compaction of the soil around the cans. And it's not always the contractor's sloppiness. It's very hard to compact the soil with pipes and can in the way. So we either backfill the excavation with slurry or CLSM (note that it's a lot of CLSM or slurry) or put in a column system down to undisturbed ground to support the slab. We sometimes use the cans to support the slab, but it usually needs some help, like columns.