Pouring a concrete box in place

[jeffg]

I need to pour a concrete distribution box for my irrigation ditch. There are already plastic pipes in place for the feed and main run so a premade box will not work. I dug out an approximately 3'x3' square between the pipes and now I just need to pour the concrete.

Which of these options would be the best approach?
1. Pour the walls first and then pour a floor after removing the inside forms.
2. Pour the floor first and then pour the walls.
3. Try to pour the floor and walls at the same time with some sort of floating form for the center.
4. Something completely different.

I assume that if I did 1 or 2 there would be some leakage between the floors and walls.

 

[Dirtydan69]

Number 3 would be my pick.

 

[matt_i]

Personally I would pour the floor first. Then have a solid, level area to stand on while forming the walls. I would rent the concrete ******** for making sure that the walls don't have any voids. Use mazola corn oil on your forms for release, non toxic and works great. I would put some rebar in the floor and bend the pieces up to eventually tie into the walls.

Leakage, potentially yes, but I would think it minimal compared to what I think are thousands of gallons you are attempting to convey. You could always do the basement waterproofing treatment on the outside if dissatisfied. I liken it to the spillway gates that don't quite seal 100%, there might be 100gpm leakage, but there are acre-feet being held back.

 

[EdT]

#3, but don't forget that the inside form box will want to float out of the hole so it'll have to be held down. Since this is not really structural, you can make the mix pretty soupy so that it flows well under the inner form box. Or you could just pour a floor and build the walls from block and fill the voids in the block after it's up. Pretty much no form work that way. I've had good luck putting block together with Gorilla Glue. It's fast and easy and, IMHO, plenty strong especially if you fill the voids in the block with concrete. I did that on a low retaining wall and tested the joint strength before I did the wall. The block failed before the joint. If this is being poured with sakrete or some other premix, get more than you think you'll need. It always seems to take more.

 

[Kev In]

You could pour the base and make a key way where the walls would be. When you pour your walls, the concrete will flow into the key way and provide a better seal between the base and the wall. You could also water proof your box or use some concrete caulking on the inside to seal it tight.

Kevin

 

[volksnick]

The keyway is smart. Cut 2x4s with a slight bevel on the outside so that they are like a trapezoid. Miter the corners so that they fit at the center line of the 4 walls. Pour the floor and imbed the keys. Once cured, runs screws into the wood and pry them out. Then form your walls and pour the walls. It locks the bottoms into the floor/footer.

As added protection, you can get a water sealant tape that you put in the keyway that swells shut when it gets wet.

 

[NCDave]

Think you might be overthinking this a bit. Put 6 of these in my back yard several years ago to change a drainage ditch to play area for the kids. Spaced them about every 30' with a bar grating top. Ran 8" corrugated with smooth liner between the boxes. Some of the boxes had gutter drain lines from the house coming in also. The ones I did were 2' square inside. Built the forms for the walls from 3/4" CDX. 2x2 cleats in the corner to tie it all together. Dug the holes about 30x30x 24" deep, recessed a 1x3 form around the top for a flange that I could finish smooth at the top of the ground with a little slope. A 3/4x3/4 cleat around the outside of the box forms gave me a ledge to set the grate top on. Poured the walls first, then poured the floor to the bottom of the out feed pipe to make sure water didn't stand. Worked slick! Make sure your concrete mix is a bit loose so it will flow and vibrate the forms either with a hammer (lots of gentle taps) or power tool (I used a reciprocating saw minus the blade). Good luck!

 

[jeffg]

Did you just set the pipe tight up against the form and pour around it for the walls?

It sound like #1 from the list above, which was my first thought.

 

[johndeereman]

#1 or #2 either will work if it was me. I would tend to lean toward option 2 as it would give you a flat level place to work up from. Or even maybe if you can get a premade catch basin to fit your size requirements.