I am going to bid a job and it requires building up the existing berm on the pond. I was wondering if I should just have scrap the black dirt of the top of the embankment till I get down to clay and be able to start building up the embankment from there or do i have to cut a key way? Also I am looking at another job where I am going to dig a holding pond and am taking the dirt from the inside of the pond and building an emankment around the outside about 5 feet high. Do I have to cut a key way for this or just get down to clay dirt and be able to start from there?
If you are trying to hold water it is best to strip all organic soils and cut a key way when building up an embankment.
I would always recommend a key-way, even if it is just a deep corner bit cut with a dozer for your embankment that is only 5' high. Also try to keep your organics out of the compacted fill to help avoid voids and piping. If you are adding to an existing berm you may have to start at the toe of the embankment and fill from there in order to obtain enough width upon completion. This depends on how wide it currently is and how much you are adding to it. Also, on small ponds this may not be necessary, but the water side of your embankment should not be steeper than 3:1, while the outside can be steeper as long as erosion will not be a problem. Hope it helps!
As already mentioned if adding to the height you may also have to widen the whole dam. If it were my job I'd cut the black dirt off and stockpile it, then cut a key into the top of the dam in the center. Preferably with the water level way down so you don't get any seepage into the keyway or collapse the top of the dam from the pressure. Then start adding compactable fill into the cut and raise the dam. When done spread the black dirt back to seal the top and add plenty of grass seed and straw. I use a make shift keyway even when fixing washed out holes in pond dams. I see you're in MO, where at? I'm south of kc bout 40 minutes. John