Pond Boss Forums POND CONSTRUCTION Building a dam clay blanket core

OK fellas, I need some advice. I am in the process of trying to repair an embankment dam for approximately a 2 acre pond. I do not know what the original dam materials consist of, and whether or not the dam was core trenched. Five years ago a contractor dredged the deep end of the pond with a drag line. That was a BIG MISTAKE. The pond is now dry. Our plan is to patch the compromised bottom with a clay mixture, and construct a blanket core on the backside of the dam, core trenched into the existing clay subsoil. Has anyone had successful results using a blanket core on the backside of an existing dam? We would like to keep the existing dam in place to lower construction costs. A blanket core on the inside (water side) of the dam was not considered because we do not want to lose water volume. Any suggestions would be greatly appreciated.

Steve,

Could you explain what a blanket core is??

Russ

Russ,

An embankment dam is typically constructed with a center (vertical) clay core that is trenched 2 to 3 feet into the clay subsoil to prevent water from leaking through or under the dam. A blanket core consists of the same clay mixture as the center core, only it is built on a 3:1 slope of the dam, either on the outside or inside (water side) of the dam. In either case, center core or blanket core, they must be trenched into the subsoil base otherwise more than likely they will leak. I don't have alot of knowlege on the blanket core, but in my situation I do not see why it would not work. If you would like to see a picture of the cross-section of a blanket core, I will send you the website that shows it.

Steve,

I would not attempt to fix a leak from the back side. To do it right it needs to be in front of the dam and done like is done in the center.

You say you do not want to lose water volume, you won't. Just dig until you reach a clay sub base ( My pond core trench was 4' deep by 10' wide for the entire length of the dam). And refill with good clay soil and make sure it is well packed.

Also, make sure there are no exposed rock vanes.

Steve,
Sounds like you are on target. But, trying to repair a leak on the backside of the dam may not work. I would certainly consider the clay blanket on the inside, even if it decreases your volume. (It won't decrease the volume much at all).
Remember this, water always seeks the path of least resistance. If there is any breach in the clay, anywhere, water will find it, and leave. So, be confident in your engineering plans and your contractor. Make someone with expertise accountable to you.

Thanks for the explanation Steve. Like Wesley and Bob stated, I would think stopping the leak on the pondside of the dam makes better sense.

Good luck with your project and keep us posted.

Russ

Thanks to everyone for their input about the blanket core issue. One thing I forgot to mention in my original message is that the dam does not meet a 3:1 slope on either side, therefore reconstruction on the inside would definitely shrink the water holding capacity of the pond. Maybe this is not a big concern since everything I've read indicates pond surface area is more important than depth or water volume. With the blanket core on the inside, we would not lose much pond surface area, and I guess we could raise the dam another foot to gain the surface area we would lose with the blanket core. We would still have 13 to 14 feet max depth, and in
southeast South Dakota, that is plenty. Thanks again for everyone's input.

Steve,

Steve.

Sorry, but I have the same problem. I hope to go down past the water line and pack clay. The back side of the dam is solid sand. I have put more than enough clay on the inside and it still leaks. I plan to core from the inside this time in hopes that it will stop the leak. I've been working on this very problem for three years.

Tony,
I don't know exactly what your situation is, but when you decide to core the dam there are some things to consider. Make sure the core trench is at least 3 feet into the clay subsoil base. The clay core should contain about 20% clay, not 100% pure clay as this could crack and lead to leakage problems. The core should be built in 6-inch layer increments and packed well before the next layer is put down. Pay attention to the moisture content of the clay mixture. It should be neither too wet nor too dry. Last, but not least, find a reputable contractor, one that knows how to build ponds. Here in South Dakota we have few contractors that know how to build a dam. Most only know how to dig basements, push dirt, and put in drain tile. Good luck with your project.

Steve,