Concrete on top of a liner in sloped area

[Okiryu]

We are designing a project where the concept design shows a concrete slab on top of a liner. This is for a secondary containment for an above-ground fuel tank. However, there is a slope (between 3:1 and 2:1) in one of the sides of the containment where concrete on top of the liner is also shown in the concept design.

My concern is about there is not too much friction between the concrete and the liner so the concrete may just slide down. I still need to check the friction coefficients between the concrete and the liner to calculate a factor of safety against sliding.

If the tank completely leaks, the level of the fuel may reach some part of the slope. But I think that if the slope is just protected with the liner (without the concrete slab) it should not be a problem (assuming that the liner will work properly).

My questions are:

1. Do you have any references for friction coefficients between concrete and impermeable liners?
2. Is it common to cover slopes areas with concrete on top of liners?

Thanks in advance for your input !

 

[darthsoilsguy2]

What liner are you using? If the liner were to fail, would the manufacturer of the liner say that your design was the incorrect application for their material? waterproofing can get tricky. membrane warranties are only as good as the designers adherence to manufacturer-recommended details and technical publications issued by the manufacturer. You don't want the membrane company to weaseling out if the product fails, call them and get guidance. waterproofing membrane warranties aren't worth much if you ever need them because of all the exclusions in the fine print, but if the manufacturer has a good case to challenge the warranty, the designer gets thrown under the bus.

I've done 2% with a cover slab for balcony detailing where you have the structural concrete balcony, a layer of waterproofing, and 2" thick finishing cover slab with tiles that the residents stand on. Even with that detail, i counted on the guardrail through posts to pin the cover slab from sliding. I think you will inevitably find that your cover slab needs to be designed to float without friction. Also consider rephrasing your question and posting in the petroleum engineering forum, or the storage tank engineering forum, search those forums first. (EDIT, i forgot to mention liner compatibility with fuel products is also something that needs vetting out)

 

[fattdad]

there could be some aspect component to this problem. What's the slope length, what's the concrete thickness and what's the liner thickness.

I don't typically worry too much about the infinite slope unless it get's close to 20:1. If there's a 1' horizon and a slope length of 20 ft, we have something to worry over. If it's a 2' horizon and a 5 ft slope length I'd think a free body diagram all that's necessary.

f-d

ípapß gordo ainÆt no madre flaca!

 

[Okiryu]

Thanks much for your input. We are planning to use a HDPE liner under the slab. We are currently checking with the manufacturer for details.

The slope is 2:1 (H:V) and about 15 feet long (inclined length). Concrete thickness is 6 inches. Liner thickness is 0.06 inches (1.5 mm). Initially, I was doing an infinite slope analysis which the FOS against sliding is the ratio between the friction angle for the concrete and liner interface and the angle of the slope.

I was provided by the attached document (Bureau of Reclamation Design Standards) and checking it, I think that a finite slope analysis is more appropriate in my case. Doing the finite slope analysis which considers the contribution against sliding of the concrete mass at the bottom of the slope, I got an adequate FOS. Conservatively, I am assuming zero adhesion between the liner and concrete (Ca and Cp are zero for the equation shown in the attached). I am also assuming very low interface friction angle between the liner and concrete (about 5~10 degrees, which gives a coefficient of friction of about 0.1 to 0.2 - [this values are just considering the tangent of the interface friction angle).

Any further input is greatly appreciated !

 

[cvg]

suggest a textured liner

http://www.gseworld.com/Products/Geomembranes/HDPE-Textured/

 

[GeoEnvGuy]

2H:1v is to steep for smooth hope, as cvg says textured.

Also you can consider concrete cloth over the hdpe which can be anchored in at the top of slope. That is if you want concrete over hdpe.

 

[cvg]

for a critical application, you may want to get a lab test to verify the interface friction rather than just assuming a value

 

[SlideRuleEra]

...the concept design shows a concrete slab on top of a liner.
This is for a secondary containment for an above-ground fuel tank.
...concern is about there is not too much friction between the concrete and the liner so the concrete may just slide down.
If the tank completely leaks, the level of the fuel may reach some part of the slope.
I am also assuming very low interface friction angle between the liner and concrete (about 5~10 degrees, which gives a coefficient of friction of about 0.1 to 0.2

If the tank does empty, then concrete is not sitting on a (dry) liner with coefficient of friction (COF) of 0.1 to 0.2.
Instead the concrete may be sitting on a (wet...oiled?) liner, probably with a COF < 0.1 to 0.2... possibly << 0.1 to 0.2.
The concrete just might slide, with the wreckage that results from sliding breaching the liner.
(A pretty pessimistic view, I'll agree, but not impossible).

If the liner is expected to actually work if/when needed (not just meet a hypothetical paperwork requirement), I would assume the COF = 0.0 and design accordingly.

http://www.SlideRuleEra.net

 

[Okiryu]

Thanks everybody for your responses !

BTW, as SRE mentioned, we are considering to use a COF of zero and use a textured geomembrane. Thanks again !