How Much Rock?

[Diggin It]

I dunno nuthin' 'bout calculatin' no volumes, so here goes......


I have an old cistern that I'm considering filling in. Reasons aren't really relevant to the topic.

It's roughly 16 feet deep and 8 feet in diameter, rounded at the bottom and top. Consider something a bit larger than Dense Grade. About how much rock should I expect to use?

 

[smstonypoint]

I will give it a shot. The formula for the volume of a cylinder = V = pi*radius[SUP]2[/SUP]*height.

In your case, V = pi*4[SUP]2[/SUP]*16 = 804 cubic feet. There are 27 cubic feet in a cubic yard, so 804/27 = 29.8 cubic yards.

Steve

Edited to correct math error.:ashamed:

 

[/pine]

It makes a difference if the space needs to be filled without any voids...for instance sedge stone that is typically used for things like riprap etc. may suffice and will not take the full volume calculated etc..

 

[Diggin It]

No, in fact I don't want it packed solid, hence the desire for something a bit larger than Dense Grade. 1-2" rock should do nicely. I'm afraid that dropping something as big as riprap 16' would possibly crack the concrete bottom.

 

[Rustyiron]

It will be at least one good tri axle dump load. Start with that.

 

[4570Man]

I’m guessing 2 tri axel loads and a smaller truck load using the previous posters math of 29.8 yards.

 

[quicksandfarmer]

It will be at least one good tri axle dump load. Start with that.

My experience with materials like that is that you never know how it's going to lay until you pour it out. You do the calculation like SMStonyPoint did -- 30 yards -- and you give that number to the guy when you call to order the material. Once he's there you tell him to keep the motor running while you figure out whether you need more. He should know that when a customer says they need 30 yards they need somewhere between 20 and 40.

 

[/pine]

No, in fact I don't want it packed solid, hence the desire for something a bit larger than Dense Grade. 1-2" rock should do nicely. I'm afraid that dropping something as big as riprap 16' would possibly crack the concrete bottom.

Without more information...why not use (much cheaper) clean fill rather than gravel?

 

[Diggin It]

^^ Because I want to be able to draw water out. The plan is to set a 6-8" pipe down the center and surround it with rock. The bottom few feet of the pipe would be perforated to allow water in but not rock. I'll drop a shallow well point in the pipe, so I don't want mud or sand in there. The cistern is old, cracked and leaking, so rainwater settles int to it. I need to be able to pump that rain water out to keep the surrounding ground dry. If it gets full and seeps out, I have a giant muddy mess next to the house.

That will also give me an emergency water supply in some sort of disaster, though it will require boiling or other treatment.

So, why fill it at all? Because it's cracked and I don't want to risk it falling in on itself.

Rock will prevent collapse, but allow water collection.

 

[/pine]

^^ Because I want to be able to draw water out. The plan is to set a 6-8" pipe down the center and surround it with rock. The bottom few feet of the pipe would be perforated to allow water in but not rock. I'll drop a shallow well point in the pipe, so I don't want mud or sand in there. The cistern is old, cracked and leaking, so rainwater settles int to it. I need to be able to pump that rain water out to keep the surrounding ground dry. If it gets full and seeps out, I have a giant muddy mess next to the house.

That will also give me an emergency water supply in some sort of disaster, though it will require boiling or other treatment.

So, why fill it at all? Because it's cracked and I don't want to risk it falling in on itself.

Rock will prevent collapse, but allow water collection.

Roger that...what we call "sedge stone" (from 2"-3" all the way to 6"-8") is used to fill obsolete dug wells and bored cisterns etc...

FWIW...with a high slump mix...concrete can be poured over the top 6"-12" to make a solid lid...the high slump will prevent it from falling through any voids...

 

[Big Barn]

I’m guessing 2 tri axel loads and a smaller truck load using the previous posters math of 29.8 yards.

^^^ agreed^^^

 

[Big Barn]

Funny how terminology varies region to region. Around here a three axle truck ( one steer and two drive axles) is called a “tandem”.

Two front steer axles and two rear drive axles is a “tandem-tandem”.

One front steer and three drive axles is a “tridem”

 

[4570Man]

^^ Because I want to be able to draw water out. The plan is to set a 6-8" pipe down the center and surround it with rock. The bottom few feet of the pipe would be perforated to allow water in but not rock. I'll drop a shallow well point in the pipe, so I don't want mud or sand in there. The cistern is old, cracked and leaking, so rainwater settles int to it. I need to be able to pump that rain water out to keep the surrounding ground dry. If it gets full and seeps out, I have a giant muddy mess next to the house.

That will also give me an emergency water supply in some sort of disaster, though it will require boiling or other treatment.

So, why fill it at all? Because it's cracked and I don't want to risk it falling in on itself.

Rock will prevent collapse, but allow water collection.

Any gravel would do that. Why go through the difficulty of trying to use big rock?

 

[Diggin It]

Any gravel would do that. Why go through the difficulty of trying to use big rock?

I don't want to use big rock. I figure 1-2" would do the job and not get into the pipe. I could drill a couple of dozen 1/2" holes in the pipe instead of a bunch of smaller holes if I used smaller gravel. I don't know of a perforated pipe that diameter available locally, though I might be able to use the 4" I can find if I knew it wouldn't crush over time.

To complicate things, I can't get a tri-axle in my driveway and I wouldn't want that much weight on my blacktop at one time. There are a couple of guys here with single axles that could bring 5-6 ton or so each load. I'd have to see how they would price multiple loads over a couple of days.

It's only about 10-15' feet off the driveway, but not in a position they can dump direct, so I'll have to do it by loader which will take time.

 

[LD1]

Where are you located?

Around here, what we call #4 gravel is what I would use. Roughly golf ball sized.

30 yards is about 45 tons if gravel. A little less if limestone.

 

[Gary Fowler]

The larger the rock, the more water it will hold for your emergency use although I don't know how you could justify putting a pump into it for no more water than you will get. For the cost of gravel and labor to install it, you could likely put a sealant into the cistern so it doesn't leak. I seriously doubt that cracked concrete is going to collapse inward on a round structure. They are pretty well self supporting. If it were square, it might fold inward, but not a round structure. Pressure forcing inward would have to crush the concrete in order to collapse, outward pressure from the water inside would have a better chance of causing a failure, but with solid dirt around it, that is unlikely also.

I would fix it to hold water if you really need the water, otherwise I would fill it in with dirt, not rock, so there is no possibility of water seepage causing mud as you now have.

 

[Jstpssng]

I did similar to what you had when I had my spring dug, except that I used 10 yards of gravel screenings. Since then I have read that it was the wrong material to use. If you use finer material it will act as a filter for water percolating down through.