Scour Around Wide Flange Pile Foundations for Solar Array

[fel3]

I am working on a drainage study for a solar array. The tracking solar panels will be individually mounted on driven wide flange piles (W6x15 IIRC). The County and the structural engineer want an estimate of the scour depth around the piles. All of the information I have been able to find (e.g. HEC 18 and about 20 other sources, including several academic papers) deal with simple cross-sections such as circles, ovals, "pointy" ovals, etc. I have not been able to find any information for estimating scour around more complex shapes such as wide flange sections. I suspect that a wide flange section generates more scour than a similarly-sized circular cross-section, but I don't know by how much. Can anyone here point me in the right direction on this issue?

Fortunately, the project site is very flat, is outside the 500-yr flood plain, and has very little upstream land for run-on flow. If the piles were circles of similar size, the scour would be only a few inches.

Thanks in advance.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[dicksewerrat]

Put a section of pipe around each WF pile. Fill with concrete. Use the round calculations.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[cvg]

calculate 3 inches, double or triple that for FS and then call it good. scour is not a concern in your area and there is no need to make this a rigorous analysis

 

[fel3]

discksewerrat…

That's a reasonable suggestion, and an idea I had also thought of. However, I have no control over the design, only the drainage analysis. For 600+ piles, the client would only do it if absolutely necessary and I know it won't be necessary.

cvg…

Your approach was my fall-back plan. I really didn't think I would find any information for scour at complex sections, but it was worth a shot. In this case, I would calculate the scour (minimal) for a circular cross-section of a similar size, then add 50% to 100% as a safety factor.

Thanks both for your input.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[beej67]

Fortunately, the project site is very flat, is outside the 500-yr flood plain, and has very little upstream land for run-on flow.

I'm not fully understanding the rationale behind them demanding a scour analysis. Do they require a scour analysis for mailboxes? Road signs?

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[fel3]

beeg67…

This appears to be a new fad here in Central California. I researched drainage studies for solar arrays prepared within the company over the past ten years or so. (BTW, all were prepared by engineers who have since left the company and I've only been here a year.) None of the old drainage studies included a scour analysis. The most recent study was completed about four years ago, then the economy tanked and we didn't do any for a while. I now have one drainage study in hand for a solar array and I am working on a proposal for a second one for a different client in a different county. In both cases, the counties and the structural engineers are asking for scour depths.

For the project in hand, I may give the scour depth by equating it to a number of sand grains stacked vertically, it's that small. The other one I can't guess yet because I don't have all the data from the client yet.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[cvg]

several of the solar studies I did were in alluvial fans / alluvial plains in the Mohave Desert. they required a scour study and a floodplain delineation. in general, scour was not a big issue. sediment deposition, culvert plugging and road washout might have been more of a risk. since the piers were 10 feet or more deep, none of the scour estimates were an issue.

 

[gbam]

I am not sure I understand the need for scour evaluation if the solar arrays are outside of the 500-Year Event. Am I missing something?

 

[dicksewerrat]

The 1000 year flood may come. But I thought Noah didn't do a scour study on the Ark. County review team doesn't have enough to do.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[fel3]

gbam…

I don't understand it either, but them's the requirements.

Fred

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill