Concrete Dam Removal

[billman555555]

I agree with everyone above, 2 excavators, one with hammer other for clean up into a 6wd articulated truck to recycle pile. However water control and release is another issue, especially if you dont know the thickness of the wall. The way i would do it is use a small trenching bucket to run a drain out and down into the lower section, then do a survey of the wall and judge what machine (especially running the hammer) is needed.

Just my 2c excluding GST

 

[Turbo21835]

There is a significant difference in hammers. Check the foot lbs a hammer for your 200 size machine has vs the foot lbs a hammer for a 30 ton size machine. Then again, if you are running a rental hammer, those tend to have been abused. Just looking at the size of the structure, assuming there is a good bit of bar in there, you are going to need 20-30% more time than your estimate of 40 hours. The bar can be a big plus for you though. Hammering on rebar tends to spread the shock load out and will help pulverize your concrete. As far as a shear or processor, those will only work if you can get the jaws open wide enough to get on the concrete, and looking at that structure, the likelihood of that is slim to none.

 

[old-iron-habit]

Shimmy, iI sent you a PM with info on a blaster we used on a hospital rock job a couple months ago. Not sure if he travels as far as you are but should be able to give you a decent cost estimate.

 

[Former Wrench]

Being in the NEPA and environmental permit game, here is something that I would look at before dewatering. Consider where and how the water is going. Make sure you don't stir up some greenies because you muddied the water where someone's favorite frog or fish lives. You don't want EPA, USACE, or the state agencies pounding on your door with nasty paperwork.

 

[Raildudes dad]

Have you thought about sawing it into managable pieces? Looks like you can get at both sides once the water is gone. A couple of local college kids that have made it into the big time. My employer has used them many times usually for sawing pavement but we cut down a bridge abutment with one of those wire saws - neat stuff.

http://concut.com/services/

 

[390eric]

I definitely think I would rent a bigger hoe/hammer. Why beat yours up? IF that's the route you go.

 

[Shimmy1]

Well, guys, it sounds like this project is going to happen this fall. The last permit will be in place in a couple weeks, and as soon as the ink is dry, it's going to be go time. I was never able to locate anybody to give an estimate on blasting it, so we're going to have to use brute force. I've been thinking over many scenarios this summer, and I'm down to two possibilities. First one is to break a small, narrow hole through the dam to let the water off, second is to push out a coffer dam and bury a 36" pipe to drain it off. The water is about 6' deep on the top side, so installing a pipe wouldn't be too bad. The dam itself is pretty crude. It appears they just basically "piled" a softer mud-mix, no rebar, and blanketed that to form the spillway. The blanket layer is only about 6" thick, and contains the only rebar except for the wing walls. Upon further inspection, about a third of the core under the blanket is completely gone. You can look in THROUGH the south wingwall, and it looks like a cave for about 30'. My main question is this. If I choose to break a hole to let water out, should I be worried about the wall holding the water giving away while I'm trying to break it out? My initial plan is to break up the spillway where it's eroded out underneath, and kind of fill the void in with the broken concrete, and then open the water side and let the water run through there. I'm thinking of about a 3' wide hole to start with, can a hammer be used in water past the punch part?

 

[ih100]

Dig a shallow bypass spillway, deepen it by stages until the water is low enough, then drop your pipe in and backfill. Just to prevent the tidal wave effect swamping someone else's land.

 

[Shimmy1]

Dig a shallow bypass spillway, deepen it by stages until the water is low enough, then drop your pipe in and backfill. Just to prevent the tidal wave effect swamping someone else's land.

There is about 300 acre/feet of water to let out. I don't believe I can get away with letting the water run through a dirt trench.

 

[gcdoty]

Just a thought, you could make a siphon to lower the lake before cutting the dam of spillway. I have a 3 acre pond and I have made a 6 inch siphon to lower the level to work on the dam. I have a 30 foot drop over the back of the dam and the water comes out faster than a fire hose. I could drop the pond 3-4 feet overnight.

I don't know all of the particulars of your job, lake size, what is downstream. Depending on materials that you may have on hand or get cheap. Setting up a couple of 10 inch siphons you could lower a pretty big lake in a few days and have control of the situation. But, if there isn't any worries about whats downstream, hammer a few holes through where you say it looks hollow and stand back.

Good luck!

 

[Delmer]

There is about 300 acre/feet of water to let out. I don't believe I can get away with letting the water run through a dirt trench.

I think he meant to use a culvert buried in a trench through the dam. I'd go right through the dam like you're talking about. You know your terrain there, six feet of drop is not what most people are expecting when you said a thousand acre feet up thread. If the water somehow washed out the slot in the concrete it's going to back up pretty quick so you'll have four feet drop, the water just won't wash through there as fast as gcdoty's 30 foot drop. That wall collapsing from the water rushing by would be the least of my worries. IF that dam is undermined where you drive an excavator over the top of it, that might cause it to be unstable, but if the water hasn't moved that dam yet, it's not going to move it when you have three feet open.

I'm thinking that is going to take a lot longer to drain than you think, like a couple days with a narrow slot. I'd probably go out there with a sledge hammer and knock a couple feet out of the upstream side where it looks hollow, come back in four days and check the progress. Rather than leave an excavator sitting waiting for the water to go down. But then I'm not in your business.

 

[Shimmy1]

Thanks for the input, Delmer. After your post, I realize I haven't posted what the plan we were able to find listed for the size of the pool. The plan said 70 acres, so I'm thinking 300 acre/feet might be more realistic?

 

[CatToy]

I watched a crew a few years ago take out a 150' dam that was a about twice as tall as yours. It was too narrow to drive on, so they build a rip rap road at the base of the dam and hammered a break in the dam on the far side to drain. They used some of the concrete to shore up the road from time to time. They could only get one excavator at a time on the rip rap, so they would hammer some and clean up some. I did have a few pictures on my phone, but that was two phones ago.

 

[Shimmy1]

I watched a crew a few years ago take out a 150' dam that was a about twice as tall as yours. It was too narrow to drive on, so they build a rip rap road at the base of the dam and hammered a break in the dam on the far side to drain. They used some of the concrete to shore up the road from time to time. They could only get one excavator at a time on the rip rap, so they would hammer some and clean up some. I did have a few pictures on my phone, but that was two phones ago.

That's basically what my plan is, if I need two excavators, I can recruit another, but I'm hoping to maybe do it with one? I know most all of you guys recommend having 2 machines, but I'm going to rent a hammer for a week, and I've had a couple of guys visit the dam personally. Both agree the concrete is rotten enough I might be able to tear open the drain hole with my ripper tooth, and potentially alot more. One of the guys did a fair bit of concrete removal in the MSP area, and he feels that 20-25 hours is going to be plenty to break it up. There is only rebar in the top 6-8" of the concrete. I can dispose of any/all the debris I choose onsite, as long as no rebar is exposed. In regards to leaving the hoe onsite while it drains, I plan on doing some scraper work while it's draining.

 

[Shimmy1]

Just a thought, you could make a siphon to lower the lake before cutting the dam of spillway. I have a 3 acre pond and I have made a 6 inch siphon to lower the level to work on the dam. I have a 30 foot drop over the back of the dam and the water comes out faster than a fire hose. I could drop the pond 3-4 feet overnight.

I don't know all of the particulars of your job, lake size, what is downstream. Depending on materials that you may have on hand or get cheap. Setting up a couple of 10 inch siphons you could lower a pretty big lake in a few days and have control of the situation. But, if there isn't any worries about whats downstream, hammer a few holes through where you say it looks hollow and stand back.

Good luck!

Gcdoty, I'm not sure why I hadn't seen your post until now, but thanks for the siphon suggestion, I hadn't thought of that. So, can you give me some info on a siphon? What kind of pipe, how to set it up, get it flowing, etc. Downstream issues are not going to be any sort of problem, this dam is on a river, and I personally have seen water going over this dam 2 FEET deep for days at a time.

 

[fast_st]

I've done one siphon using 10 inch black flex drain pipe its rubber gasketed, got some 20 foot lengths made a plywood plug held in one end with drywall screws, then fill the pipe all the way, keep both ends submerged and pull the drywall screws and get ready for a torrent. It was a little tricky getting the pipe filled using a trash pump but with some careful lowering it all worked well.

 

[Shimmy1]

I've done one siphon using 10 inch black flex drain pipe its rubber gasketed, got some 20 foot lengths made a plywood plug held in one end with drywall screws, then fill the pipe all the way, keep both ends submerged and pull the drywall screws and get ready for a torrent. It was a little tricky getting the pipe filled using a trash pump but with some careful lowering it all worked well.

Any wild guesses how many gallons per minute it was moving?

 

[CatToy]

Any wild guesses how many gallons per minute it was moving?

You can use this calculator, just need to figure out what the water drop is from the siphon suction to the discharge.

http://www.calctool.org/CALC/eng/civil/hazen-williams_g

Doing some fast calcs, using a 10" pipe, with 6' drop and 30' of pipe, it would take around 10 days to drain 300 acre feet of water... my math could be wrong so take at face value.

 

[Delmer]

So is this just upstream from the junction with a larger river? It doesn't look like any flow besides leakage in the pics?

In any case, it seems like very low risk to knock a 3' slot in the dam and let it flow, a day or two should drain it as well as it's going to.

 

[Shimmy1]

So is this just upstream from the junction with a larger river? It doesn't look like any flow besides leakage in the pics?

In any case, it seems like very low risk to knock a 3' slot in the dam and let it flow, a day or two should drain it as well as it's going to.

Not really. The James River flows completely through SD before joining the Missouri River. Here's a topographic map of the area. The dam is the black line through the river.
http://map-pass.mytopo.com/maps/pri...lat=47.683335&lon=-99.452067&orient=1&res=144
No, it's not flowing right now. Just a little trickle from what I could see this morning.