Settlement and PVR Tolerance for Refrigerated Propane Tanks

[kapoA]

Need to resolve as what soil remediation is needed (if any) for a propane tank foundation.

Here is more information:

The site has stiff expansive clays. PVR estimate by geotech is about 4-5 inches (for empty tank condition - less than 1 psi load).

when the tank is half full the load is about 8 psi and the PVR is about 1 inch.

Tank Designer is insisting that empty tank condition should be considered while selecting soil remediation measures. In this case, undercut below tank bottom is about 8 feet.

Do you think that the empty tank condition along with excess moisture change resulting in PVR is a realistic condition?

The tank builder is concerned that cyclic movement of more than 1 inch will damage the cellular glass insulation provided below the tank bottom.
How much movement can the glass insulation take?

Please advice on the above two questions. Any pointers to references would be very helpful.

Thanks for your Help.

-KapoA

 

[TXStructural]

I would count on the higher PVR, if for no other reason than that any number of things could result in differential soil expansion, which could be worse than level vertical movement greater than the one inch limit.

As far as the allowable movement for the insulation, that is up to the insulation and tank guys. If the tank and insulation are supported by the same slab/footing, if seems like they would be moving together.

 

[kapoA]

8 feet of undercut for each tank 150 ft in diameter is resulting in a lot of earthwork.
If calculated over 6-8 tanks, the cost and time for this earthwork is a significant percentage of project cost.

Is there an alternative to "undercut and replace with fill" option that is more cost effective?