Oiled sand tank foundation

[sdz]

My company specifies a layer of oiled sand under steel tanks. Is this good practice?
If not, then why? and what are the alternatives?
API 650 mentions the use of "clean sand" but does not say anything about "oiled sand".

 

[BigH]

I've never used nor have I ever seen my company specify oiled sand for large diameter tanks. We normally use/have used granular tank pad foundations (well graded crushed stone for the most part) without concrete ring walls topped with a 75mm layer of fine crushings - for leveling and ensuring no 'hard' spot (angular tip of agg piece) that the steel would rest on.

 

[JedClampett]

Oiled sand is pretty obsolete. The worry is the oil will migrate into the groundwater. We've tried to specify food grade oil, but it was too expensive.
Compacted aggregate base is an acceptable alternate, as long as it doesn't have any material in it that would corrode the tank bottom (happened to us).
Asphalt is another alternate. Contractors work with it all the time, it can be shaped such that the floor slopes can be maintained, it shouldn't be corrosive and the price isn't a big objection. But I can't remember ever using it, just suggesting it.

 

[BigInch]

Oiled sand bases under tanks was common at one time. I don't know if it is still a preferred method of installation. Now that so much attention is given to having the capability to detect leaks below tanks, I would think that oiled sand would not help.

http://virtualpipeline.spaces.msn.com

 

[sdz]

I have found that oiled sand is recommended in AWWA D100-05 Sect 12.6

 

[RWF7437]

sdz,

You are correct. AWWA D-100 specifies oiled sand foundations and they have been used for many years. As far as I know there have been no major problems with them for steel water tanks but others may know some reason not to use them. I've spec'ed them several times myself and base my remarks on only this limited experience.

Others, especially steel tank providers, will have much more experience to draw on.

good luck