Cistern

[WVBill]

Darren:

Any chance you could post some pictures to help us (me anyway) visualize the situation?

 

[heehaw]

sure sounds like you've already done a lot of work, with a bunch more to go. sometimes its best to cut bait and start all over..any chance of putting this system closer to your house, so you could catch the roof runoff, and then put a pump in the cistern to get the pressure you are looking for in the location your using now..pumps are cheap and last a long time.
heehaw

 

[Darren]

For whatever reason when the house was built sometime in the 1860's, it was placed on the point of a small plateau which is also the lowest elevation on the plateau. The kicker is that there's no space immediately near the house to sink a cistern. Within a short distance of the house the ground either drops off abruptly or rapidly goes uphill.

One of these day's I'll have to look into a digital camera. I have a few pictures of the cistern excavation that I might be able to get scanned.

 

[Anonymous Poster]

I think in the old days cisterns were plastered to prevent leakage. You also would most seriously want to look into lining it with bentonite clay first - some weird stuff, stops moisture. I would really, really look this up. Good to get it right, impossible to redo if it's wrong! Concrete silos were plastered too to make the air-tight. You need to talk to those types of people.With the steep slope you are on, you need to worry about water pressure (& frost, made worse by water pressure) on the concrete when it is empty. you could be in the middle of a spring, & that will cave in a side if the cistern is empty. I think you might want some gravel & drain around it. Again, something I would really look into - hillsides are known for this!You said it is 50' long, is your cement mixer on an end or the middle of a side? It wouldn't seem very hard to chute the concrete into the bottom if you are on the middle of a side, wouldn't take that long of a chute. You might need a lot more labor than you think, get some folks down there with wheelbarrows, shovels, & levelers... I too would worry about cracks forming, since this doesn't seem like it will be a single pour. I have no solutions or ideas for this.I don't understand your point about just digging deeper to increase capacity, as you've said you hit rock, & once the concrete is poured, you will not be digging any deeper!Why did you need 100' of fall? My livestock is fed from a more conventional round cistern 60 years old. The bottom of the cistern is about 4-5 feet above the faucet level in the barn. With inch & a half pipe, I've got water for 40 head of cattle, could double that & not worry about flow rates.... I'll assume you just have a difficult location & this is all that works, but you sure could have gone with less head.I think you have studied this better than we think, & I'm not trying to talk down to you, I'm sure you've planned & consulted for much of this already. Just tossing out those whacky ideas.--->Paul

 

[Darren]

I don't take anything someone says as talking down to me. There's a lot of experience on this board. If nothing else through the years I've learned that you can't plan enough and ask enough questions. Every suggestion and comment stokes the brain. I may come across a bit short at time but that's not the case.

Waterproofing is a major issue. Usually a surface treatment using something like Thoroseal does a good job. What I've been looking at is other ways of making concrete impervious. One that's used for bridge decks and parking structures is silica fume also called micro silica. The particle structure is so fine it's very effective at filling the microscopic voids in concrete that permit the passage of water. It's finer than cement.

I've talked to the block plant and got their agreement to incorporate silica fume in the block mix. The same additive can be used in the mortar, the grout for the cells and the slabs. It turns out I'm a few hours away from a major source which helps since it's not normally stocked by concrete suppliers and I'll need a couple of pallets of the stuff.

Since a cistern in use is constantly exposed to water, another concern is the use of anything that can cause spalling later. I've already bought a 4" stainless steel drain.

I also came across a surface treatment that utilizes a chemical reaction to seal block and concrete. It is approved for potable water use.

Among the things I have to do is layout the work area and see how everything will fit in. That's a major concern. The pit is only accessible from one end. There's some room on the uphill side but I'm not sure it's enough to park the mixer and provide access for loading.

I'm going to do a trial run on something that needs a couple of yards to look at cycle time. I may have to use an additive that retards setting time to eliminate cold joints just in case.

The reason for the height is that I want to be able to run the water system without a pressure tank and switch and still have at least 40 psi. I'm working with something over 100' of elevation difference. Because of access problems, fire insurance is more expensive. I don't expect the premium to go down, but having 40 or 50,000 gals of water feeding a high pressure pump might make a difference if there's a fire.

For backfill, I'll be using clean sand wrapped in geotextile to minimize active earth pressure along with a perimeter drain around the base. Like you said, I'll only get one chance to get this right. I'll have a local engineer design the structure. I'm not doing this by the seat of my pants.

I did find some pictures of the site that I'll post after I get them scanned.

 

[Anonymous Poster]

For ponds we use rubber roofing a 20 x50 rollis about 350$. Wouldn't even need a frame just dig a hole and line it. Charcoal filter on the outlet. You could also build out of wood easier and probably cheaper and line it with it.

 

[Anonymous Poster]

Don't know how close you are to Winston Salem, but there are 100+ epoxy lined steel tanks on the market there, from a soft drink plant, being offered for sale at 25 cents a gallon of capacity. Sizes range from 20 to 50 k gallons.
Phone number if you're interested is 717-426-4919

 

[Soundguy]

Even grouted walls are going to leak. ( I'm a Civ-Eng.... I see it all the time...... Unless it is epoxy lined or something similar.. but better watch out for setteling.. will crack that concrete.. even if reinforced... )

Be thinking about a liner.. possible a pond liner. Most landscaping or pool places can get these.

Soundguy

 

[Darren]

A certain amount of leakage wouldn't be a problem. From what I've seen walls properly coated with Thoroseal don't leak. The other sealant I have to check is one that's approved for potable water and involves a chemical reaction.

How familar are you with silica fume used to eliminate intergranular voids in concrete used for parking garages and bridge decks?

As for the concrete settling, I'm down to solid rock. As long as I pour a working slab first before the cistern slab, I don't see how settlement is an issue. Other than the possibility of an expansion/contraction crack, what else could happen? As long as I eliminate settling, how do I prevent cracks or use waterstop and a built in expansion joint to eliminate cracking?

FWIW, a large tank isn't doable. There's no way do get something that size and weight on site. The ex-soft drink tanks have been available out of Baltimore. The weight and size make them impractical.

 

[Anonymous Poster]

Thorough seal can leak....if the walls crack after thorough seal has already been applied.Been there done that,a round concrete cistern will hold water better than a square cistern,a square cistern can cause you problems in the corners..Ever consider using something like a silo stave ?