tank foundation recommendations

[matrixeric]

Hello All:
I am a structural engineer and have been recently assigned with the job of designing the foundation for a water storage tank (26' dia x 35' high). From my online/literature research I see that the options for the tank foundation are either a crushed stone ringwall or a concrete ring wall or a reinforced concrete slab.

A question I have to my fellow engineers is: Who makes the call or recommends the type of foundation suitable for the tank? Is it the Geotechnical Engineer or the Structural Engineer? My hunch is that that the Geotechnical Engineer must advise on the type of foundation (one of the above mentioned types)and shoud not just state in his/her report that a shallow footing is recommended for the structure at the site.

Thank you for your comments/advise/opinion.

 

[JStephen]

If the tank is to be anchored (likely the case with those dimensions), the crushed stone ringwall is out.

If the weight of the water exceeds the allowable bearing, the ringwall is out.

Usually, the owner will specify whether it's a concrete or gravel foundation based on serviceability issues (concrete is a better foundation at a higher price). Choice between slab and ringwall may be specified by the owner or left to the foundation designer or contractor.

 

[ATSE]

See AWWA D100 and D103.
If you are in seismic country with SDS > 0.4g, I would not entertain a gravel foundation, even if AWWA equations permit.
A concrete ring not only provides something heavy to anchor to, but also reduces the differential displacement along the shell perimeter due to subgrade stiffness variation, which can manifest itself in additional wall stresses, and wall buckling in extreme cases.

 

[msquared48]

The Geotech recommends the values for the possible foundation types and may prefer one in writing.

It is then up to the Structural engineer to design one that works based on the values given by the Geotech.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[JedClampett]

Hey, matrixeric, cross posting the same question in multiple forums is not encouraged. And what if you were to get different answers? Would you post this in another forum?

 

[matrixeric]

Thank you all for the comments ...
My apologies for posting it on two forums as I wasn't aware of the etiquette and this will not happen again ... all i was trying is to get the opinion of both structural and geotechnical engineers ...Thank you Jed for bringing it to my attention.

 

[echelon22]

We always used the concrete ring beam with a thinner slab running around the outside to support the jacks (these tanks were erected starting with the roof, then jacking up and bolting the next run of panels on etc).

We only added an internal slab if we needed utilise the mass of the water to help with seismic sliding resistance, otherwise it was just a liner on a crushed rock base.