# Coefficient of friction between soil and steel



## DJR (Jan 16, 2008)

I am doing a design of a 500,000 gal tank in CA, and am trying to check the resistance to sliding on it. We will be using a ring beam foundation with 6" of crushed base in the middle of it. The tank manufacturer is providing a 1/2" thick fiberboard that will be placed between the tank and the foundation/crushed base.

Is anyone aware of a "standard" coefficient of friction between this fiberboard and base? I am assuming a coefficient for fiberboard to soil would work to. Or if worst comes to worst, a coefficient for steel to the base.

Thanks.


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## MA_PE (Jan 16, 2008)

DJR said:


> I am doing a design of a 500,000 gal tank in CA, and am trying to check the resistance to sliding on it. We will be using a ring beam foundation with 6" of crushed base in the middle of it. The tank manufacturer is providing a 1/2" thick fiberboard that will be placed between the tank and the foundation/crushed base.
> Is anyone aware of a "standard" coefficient of friction between this fiberboard and base? I am assuming a coefficient for fiberboard to soil would work to. Or if worst comes to worst, a coefficient for steel to the base.
> 
> Thanks.


Just curious, what's going to make a 500,000 gallon tank slide? I can't envision enough unbalanced load for that to happen. I'd estimate that 0.3 would be conservative.


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## whitley85 (Jan 16, 2008)

NAVFAC gives a value of 0.4 for clean steel to gravels. Hope that helps.


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## DJR (Jan 17, 2008)

MA_PE said:


> Just curious, what's going to make a 500,000 gallon tank slide? I can't envision enough unbalanced load for that to happen. I'd estimate that 0.3 would be conservative.


MA PE - The CBO is requiring that calc for the high seismic load. It does seem unlikely, but from my initial calcs, it would be possible if it is not supported properly.

whitley85 - thanks for the info.


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## ODB_PE (Jan 17, 2008)

DJR said:


> I am doing a design of a 500,000 gal tank in CA, and am trying to check the resistance to sliding on it. We will be using a ring beam foundation with 6" of crushed base in the middle of it. The tank manufacturer is providing a 1/2" thick fiberboard that will be placed between the tank and the foundation/crushed base.
> Is anyone aware of a "standard" coefficient of friction between this fiberboard and base? I am assuming a coefficient for fiberboard to soil would work to. Or if worst comes to worst, a coefficient for steel to the base.
> 
> Thanks.


what exactly does 1/2inch fiberboard accomplish under this thing? What is the effective psf?

I'm just curious.


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## MA_PE (Jan 17, 2008)

Assuming that the base is a fairly thin sheet of steel (not really suporting any loads just there for watertightness) the fiberborad would provide a more uniform contact surface on the steel membrane and minimize point contacts from the gravel base. It doesn't really matter if it crushes it still would provide some "cushion"


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## H-man (Jan 17, 2008)

How deep does the ringwall extend below the ground surface? Would the ringwall installed in the soil provide any passive resistance against your seismic forces?

Is the fiberboard placed directly on the 6" of granular material?

Besides the benefit of providing a uniform bearing surface beneath the tank (credit to MA_PE) I am wondering if the fiberboard would prevent moisture from reaching the underside of the steel tank floor (capillary rise?).

I am a prestressed concrete tank designer (but have tried to present points in a neutral manner).

MA_PE - I will be rooting for the PATS this weekend.

H


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## MA_PE (Jan 17, 2008)

H-man said:


> How deep does the ringwall extend below the ground surface? Would the ringwall installed in the soil provide any passive resistance against your seismic forces?
> Is the fiberboard placed directly on the 6" of granular material?
> 
> Besides the benefit of providing a uniform bearing surface beneath the tank (credit to MA_PE) I am wondering if the fiberboard would prevent moisture from reaching the underside of the steel tank floor (capillary rise?).
> ...


Actually, I was thinking that the fiberboard may HOLD moisture against the tank bottom. I'd think a plastic vapor-barrier type membrane between the fiberboard and the steel might be a better detial. Alternatively just use some styrofoam insulation. It won't absorb water and would smooth out the bearing surface.

It looks like we may be in the minority here but GO PATS!!


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## ODB_PE (Jan 17, 2008)

MA_PE said:


> Actually, I was thinking that the fiberboard may HOLD moisture against the tank bottom. I'd think a plastic vapor-barrier type membrane between the fiberboard and the steel might be a better detial. Alternatively just use some styrofoam insulation. It won't absorb water and would smooth out the bearing surface.


I'm in your camp. I think 1/2" Fiberboard would be a liability in this situation - like a damp sponge there for eternity. I would however, question the ability of 1/2-inch fiberboard to distribute loads that much if at all. At those pressures I reckon the unevenness will translate through the surface - especially once it gets wet. But I don't design storage tank foundations, so what do I know....


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## H-man (Jan 17, 2008)

I agree the fiberboard would soak up moisture if the fiberboard is wood based. However if high density roof fiberboard made for roofing is used (www.gp.com/build/DocumentViewer.aspx?repository=BP&amp;elementid=2996) then I believe it would limit the amount of moisture.


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## DJR (Jan 18, 2008)

The full description of the fiberboard is "asphalt impregnated fiberboard", so it is a higher-quality product than a wood-based one.


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## kevo_55 (Jan 19, 2008)

I'd have to agree with MA that a coeff of friction of 0.3 would be a good starting point.

As for the moisture problem, is there enough engineered fill in the area to allow for drainage and make moisture not a problem? Or... is this going in the bay area?


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## DJR (Jan 21, 2008)

We are west of Fresno, and the water level is about 190 ft below grade, so moisture shouldn't be too much of an issue.


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