Structural design of water tank 6

[Gulmitic]

Hello Guyz,

I have designed (structural) an underground water tank, but am not sure if about the results. Are there any links on the internet that design underground water tanks?

 

[rconner]

You may be interested in the thread at

http://cr4.globalspec.com/search/si...rt=textmatchrank&srch=underground water tank.

 

[bimr]

If you are posting about a potable water tank, it should not be an underground tank. At least 50% of the potable water storage volume is required to be above grade.

 

[JedClampett]

Hey bimr, that's a new one to me.

 

[Maury]

Article 7.0.2(c) and (d) of the Ten States Standards:

"If the bottom of a storage reservoir must be below normal ground surface, it shall be placed above the grouundwater table. At least 50 percent of the water depth should be above grade. ..."

"The top of a partially buried storage structure shall not be less than two feet above normal ground surface. ..."

 

[cvg]

doesn't apply in the other 40 states...

 

[JedClampett]

....or we have a lot of potable water tanks out of code.

 

[RWF7437]

Not only doesn't apply to other 40 states; it doesn't apply to systems other than wastewater systems. Nor, is it likely that it provides detailed "structural" design guidance.

For buried concrete tanks, the Portland Cement Association, and others, offer a great deal of information on structural design.

Google their websites.

good luck

 

[bimr]

The state guidelines set forth by the various states {outside the ten states area} for construction of water storage facilities are similiar to the guidelines found in the ten states. Here is an excerpt from arizona:

Specific requirements for finished water storage units are as follows:

a. The bottom of ground storage units shall be placed at the normal ground surface and shall be either above the 100 year flood level or protected from the 100 year flood.....

b. When the bottom of a storage unit must be below normal ground surface, it shall be place above the high ground water table......

http://www.azdeq.gov/function/compliance/download/eb10.pdf

After completion of the review, and approval of the plans, the department will issue an ATC Certificate. Projects are reviewed for conformance to state rules and regulations (A.A.C. Title 18, Chapter 4 and Engineering Bulletin No. 10) and sound engineering practice

Sound engineering practice is to not bury a potable water tank, for somewhat obvious reasons.

 

[jgailla]

cvg,
In Florida, they have referenced the "10 states" as the governing standard, so we would be down to 39. I suspect other states have also adopted the "10 states" standards.

 

[bimr]

Alabama, California, Delaware, Montana, Arkansas, Nebraska, Vermont, Kentucky, Mississippi, Utah, Idaho .... all reference Recommended Standards for Water Works, commonly referred to as the Ten States Standards.

 

[rconner]

One definition of a “tank” (at least generically according to my Webster) is, a “large receptacle for holding, transporting, or storing liquids.” While it appears the liquid the original inquirer wants to hold is water, from the brief information supplied I don’t know for sure at this point that what is quoted in the Ten States Standards would specifically apply (I think several well-intentioned folks are assuming this is for finished water storage, and indeed that may well be the case, although I don’t recall that being described in the original inquiry). All that is stated in the Ten States Standards can now be read in context at e.g.

http://10statesstandards.com/waterstandards.html

(but I did happen to notice also the section, “7.0.8.2 Ground Level Structures a. Each manhole shall be elevated at least 24 inches above the top of the tank or covering sod, whichever is higher” may now be argued to be at least a little confusing, if it is meant to apply to only allowable aboveground tanks!)

 

[cvg]

requiring manholes, lids etc to be 2' above the ground is good practice to avoid storm runoff from entering the tank. Placing a tank above the normal water table is also advantageous to avoid "floating" the tank. Requiring half the water storage to be above grade - don't know what the basis for this recommendation is and seems somewhat arbitrary and would possibly conflict with allowing the tank to be below ground. I hope the original poster is in the US as I am sure there would be different standards to follow if he is not.

 

[bimr]

"Requiring half the water storage to be above grade - don't know what the basis for this recommendation is and seems somewhat arbitrary"

Since, water storage tanks are not pressurized, any cracks in the tank walls would allow potentially contaminated water to enter into into a buried tank.

 

[cvg]

however, the same regulation does allow tanks to be constructed below grade. Proper design of the tank will prevent the cracks. Apparently this is a 10-states requirement but certainly not in many other areas (Arizona being one). And if it is constructed above the water table, there is not likely to be contaminated water or sufficient pressure for any water to enter into a tank.

 

[bimr]

however, rhe arizona recommended standard was posted above and it is calling for:

a. The bottom of ground storage units shall be placed at the normal ground surface and shall be either above the 100 year flood level or protected from the 100 year flood.....

b. When the bottom of a storage unit must be below normal ground surface, it shall be place above the high ground water table......

http://www.azdeq.gov/function/compliance/download/eb10.pdf

 

[cvg]

I have read the AZ standards and practice in AZ and CA. I think we are on the same page as I firmly believe placing it below the high water table would be folly. But if the water table is at 200 bgs and you want to construct the tank below ground to keep the water cool during 114 degree days in phoenix, why should you be required to keep an arbitrary 1/2 the water surface above ground?

 

[civilperson]

The engineering reasons to not bury a water tank are not obvious to me. Not a lot of cracks in steel or plastic lined tanks.

 

[bimr]

The reason that a tank operating at atmospheric pressure should not be buried is somewhat obvious.

In sewers, you get something called I/I. The same thing will occur in a buried tank and will result in contamination of the potable water.

 

[civilperson]

Inflow/infiltration is not a factor in steel tanks or plastic lined tanks, (and probably not applicable to reiforced concrete above the saturated soil elevation). Your use of sewer standards for water is misapplied.