Piled foundation fitness for service 2

[ultrazero]

Hello all!

Does anyone know a fitness for service plan for piled tank foundations under a storage tank?

API 653 appendix B addresses settlement of tanks on soil, or on a ring wall. It does not cover a tank on a concrete pad supported by friction timber piles. We can measure the edge settlement around the tank. But the settlement pattern of a piled foundation tank must be different from a tank on soil. Aside from checking the appearance of the concrete for defects, are there other ways? I am concerned that following API 653 appendix B may not be sufficient.

Please note that I have sufficient info on designing a piled foundation. The inquiry is how one can tell whether an existing piled foundation is OK for continued service. In some situation, the pile log info is not longer available. This means the pile capacity and the pile quantity are not known.

 

[JoeTank]

All of the API documents (API-653, 510, 570 and 579) deal only with the pressure retaining boundary. The foundation FFS will have to be developed by a Storage Tank Engineer using the best engineering judgements and experience that he can muster. If this is an asphalt tank be very concerned about deterioration due to elevated temperatures. A number of timber piled tank foundations have failed in recent memeory due to degradation of the wooden piles.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[BigH]

SteveBraune - interesting about deterioration of timber piles of tanks. Question: Were the piles continually below the water table or were the piles subjected to wet and dry cycles? Could be one reason for the timber deterioration. The heated environment could be detrimental in that the heat may promote biological activity and hence possibility of timber rotting.

 

[ultrazero]

Steve,

Thank you very much for your insight. You confirmed what I know up to this point. API documents do not address FFS for concrete foundation on piles.

This is what I found from literature (caution: not from field experience): Timber piles last indefinitely under water. It can be attacked by insert, fungus, etc. if above the water. Treating piles with creosol extends the life. There are other reasons that timber pile foundations can fail - negative skin friction, group settlement, lateral load, excessive load, soil erosion, soil liquefaction, seismic event, pile buckling, etc. This is why geotechnical engineers use a safety factor of 2.5 to 3. (Moot if piles disintegrate under the foundation.) Problem with pile foundation is that once it is built, it is not easy to tell if it is OK afterwards. Having engineering drawings, pile driving record and soil boring report helps. Without them make it even more challenging for a foundation FFS evaluation.

Even with the uncertainties mentioned, I shall appreciate insights on what can be done to determine if a pile foundation is OK.

Ultrazero

 

[JoeTank]

Big H,
I don't believe that the wet-dry issue was present on the three failures I am familiar with. The piles temps were just too high for the wood to sustain.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[SlideRuleEra]

Ultrazero - Perhaps you could consider the rough equivalent of a pile load test, but on the entire foundation, as a unit:
1. Start with an empty tank and measure numerous, specific top of foundation perimeter elevations.
2. Fill the tank in discrete stages (with water or product), recording the foundation elevations at each stage.
3. Empty the tank in stages, again recording the elevations at each stage.
4. At the perimeter location with the worst differential settlement/ rebound characteristics excavate a pit, down to the water table if possible. Inspect/core a pile(s) to get an idea of status.

Unless you have conditions like those described by SteveBraune, the worst deterioration most likely will have happened at or near the top of the water table. Wet/dry cycling is typically the worst environment for timber, even treated (creosoted) timber.

 

[ultrazero]

Dear SlideRuleEra,

Thank you very much for your insight.

Would you mind to quantity your answer? Say, formula, specific settlement value, or rebound value, as the criteria for acceptance or rejection?

Ultrazero

 

[SlideRuleEra]

Ultrazero - Since you have very little information on the foundation, the actual amount of settlement/rebound will be of limited value. However, if you compare the settlement of each "spot" on the perimeter with all the other "spots" you may see one (or more) that standout as having had "worse" settlement/less rebound than the others. This would be the location on the perimeter to dig the pit.

Pile load tests are covered by ASTM D1143. However what you have described go beyond the scope of a "normal" test - I doubt if you will find ANY exact criteria to apply to the situation. This is one of those cases where "engineering judgement" will most likely be needed to make a detemination of the foundation's acceptability. You may need to contact a qualified engineering consultant to get the specific level of experience needed.

 

[ultrazero]

Thank you all.

I am getting a handle on this. We are contacting an expert for a further evaluation.

Ultrazero