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Gulmitic (Civil/Environme)
13 May 08 8:46
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 (Civil/Environme)
13 May 08 9:34
You may be interested in the thread at http://cr4.globalspec.com/search/sitesearch?do=show&srchobjs=t%2Cc&fs=10&order=asc&sort=textmatchrank&srch=underground%20water%20tank.
bimr (Civil/Environme)
13 May 08 9:43
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. 字串9
JedClampett (Structural)
13 May 08 11:26
Hey bimr, that's a new one to me.
Maury (Civil/Environme)
13 May 08 12:13
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 (Civil/Environme)
13 May 08 15:04
doesn't apply in the other 40 states...
JedClampett (Structural)
13 May 08 16:35
字串2
....or we have a lot of potable water tanks out of code.
RWF7437 (Civil/Environme)
13 May 08 17:24
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.
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bimr (Civil/Environme)
14 May 08 1:33
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..... 字串4
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 (Geotechnical)
14 May 08 8:48
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 (Civil/Environme)
14 May 08 10:06
字串2
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 (Civil/Environme)
14 May 08 10:28
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!)
字串5
cvg (Civil/Environme)
14 May 08 11:32
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 (Civil/Environme)
14 May 08 16:22
"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.
字串4
cvg (Civil/Environme)
14 May 08 16:27
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 (Civil/Environme)
14 May 08 21:32
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...... 字串7
http://www.azdeq.gov/function/compliance/download/eb10.pdf
cvg (Civil/Environme)
15 May 08 10:51
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 (Structural)
16 May 08 12:45
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 (Civil/Environme)
16 May 08 13:22
字串4
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 (Structural)
16 May 08 13:31
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.
bimr (Civil/Environme)
16 May 08 17:51
In a perfect world, there would be no water leaks, no crime, no rusting, no poor soils, everyone would be above average.....
However, this is not a perfect world.
Nobody makes large (greater than 30 ft dia.) buried tanks out of steel or lined plastic. Steel tanks are more commonly designed for atmospheric pressure. Plastic linings are desiged to protect the tank walls from corrosion, not to prevent leaks. This is something that an experienced civil structural would call common practice. 字串5
Large buried concrete tanks will settle and crack over a period of several decades allowing minor leakage and contamination into the tank, not out of it.
Unlike a pressurized tank, where the flow is outward, a large empty buried tank will be subject to the same phenomena known as I/I.
You are the second person on this thread to post that the Ten States Standard is a sewer standard. Not sure where you are getting your information:
Article 7.0.2(c) and (d) of the Ten States Standards is not a sewer standard.
http://10statesstandards.com/waterstandards.html
RWF7437 (Civil/Environme)
16 May 08 19:28
There are hundreds, if not thousands, of buried potable water tanks in service. Mosr are designed under AWWA standards, State Health Division standards and structural standards of ASCE, CRSI, and others. I have designed dozens, mostly conventionally reinforced concrete, although some pre-stressed tanks exist below grade. Most are placed on hillsides or hilltops where groundwater, if any is present, will flow away from the tank. 字串9
They come in all shapes and sizes from a few hundred gallons to millions of gallons. All are leak tested periodically. Some have their roofs exposed and are used for recreation areas such as tennis courts, urban parks, etc.
I have never heard of a case of contamination by groundwater leaking into the tank. If such cases exist they appear to be very rare.
Among the advantages if burying a tank include:
stable temperature in hot climates
no need to repaint or recoat the tank exterior
ease of monitoring leakage into or out of the tank
aesthetics
long life ( some such tanks have been in service without problems for over 100 years)
Burying half the tank appears to be arbitrary and accomplishes what ?
At one time in history, the Ten State Standards were strictly wastewater standards but, it appears, they have grown in scope over the last 40 years since last I looked at them. In Oregon, where I live and work, and in California and Washington the Ten State standards do NOT apply. 字串7
None of this answers the original posters question which was about the structural design of such tanks so I apologize to him or her for digressing.
bimr (Civil/Environme)
17 May 08 16:21
On the contrary, RWF7437, there is no way you can design a tank without knowing what is going to be stored in the tank, as well as the other particulars such as soil condition, weather, site layout, etc. The original poster provided little of that information.
If the original poster is not sure of how to design a concrete tank, reminders of what codes and standards to follow should be considered friendly advice, not an opportunity to debate others.
For example, if he was designing a concrete oil/water separator, you might refer him to the API. If water, then to the AWWA. If wastewater, then to etc.
The title of the post is actually "water tank". So referring someone to the Ten States Standards for Water is not out of line. While it is true that there are some jurisdictions that do not reference the Ten States Standards, many of details of the Ten States Standards have been copied into the standards of these other jurisdictions anyway. 字串5
Re: "ease of monitoring leakage into or out of the tank" How do you accomplish this? One would think that this is more easily done with an above ground tank.
Lastly, it is probably not good advice to recommend that someone pick and choose what standards to follow just because a person doesn't understand the reason for the standard.
Gulmitic (Civil/Environme)
19 May 08 12:02
Thank you all for your tips, they were all very helpful.
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