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#112202 03/20/08 02:30 PM
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Hi everyone. Someone from another forum suggested that I post on this site regarding a bulge in my dam. The dam is clay and holds about 16' of water. The pond is about an acre. It is about 16' wide on top which is a driveway. Last summer I noticed an area about 1/2 way down the dam that seemed to be muddy all the time. The pond is full for the first time now (its about 4 years old, had to drain it once to fix a leak on the bottom from mining core hole 2 years ago) and the muddy area has gotten bigger. It's about 1/2 way down and approx. 10'x 20' and bulging maybe 6" to 8". The entire dam is about 240' long. There is not any noticeable dip in the road, however I am concerned about heavy loads going over it now. I wanted to get a few loads of stone delivered and the loaded trucks probably weigh around 50,000 lbs.

Should I try adding bentonite to the water, or am I going to have to drain the pond and add it to the side of the dam? Or are there other options? I read some posts before I posted and I noticed several people mentioning that clay dams leak. But I don't know if they are referring to ones that are also used as roads.

Thank you,
Jeff

Jeff244 #112207 03/20/08 02:59 PM
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Hey Jeff244....welcome, sir.
Whoa...you're spookin' me with the muddy bulge description. You should be getting a number of questions and suggestions here shortly, but let me kick it off.
Were you present when the dam was constructed? Was a core trench cut the length of the dam? What kind of material was replaced into the core and the dam that it supports? (ie; clay content, any rocks or gravel or sand..and if yes, how much) How was the core and dam material laid in? (ie; layered in 6" - 9" layers and compacted by the dozer, a rubber tired scraper, a sheepsfoot, etc). Is the area adjacent to any pipes that run thru the dam? Do you have a way to draw down the water?
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Based on your intitial input, I would not run anything across the dam until I was assured of structural integrity. Yes, all dams leak to some extent, but the description you offer is not normal.

Brettski #112211 03/20/08 03:25 PM
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Thanks for the reply, Brettski.

At the time the dam was built I lived about 400 miles away, I was there one day during construction, other than that I saw some pictures taken by others. There was a core trench dug, I believe it was about 8' deep. The material is a reddish clay and it is mixed with some gravel. It was put in layers and compacted with a sheepsfoot. I don't know how thick the layers were though. The area is on the opposite side of the overflow pipes. The only way to draw the water down would be a pump( or wait for it to collapse :)).

Because of the slope of the land, the bottom of the dam is probably 25' of more below the roadway. If it did collapse, it would flood a road that is about 150' away and 10' or so lower than the bottom of the dam.

Thanks,
Jeff

Jeff244 #112218 03/20/08 05:20 PM
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Hi Jeff.

You're describing an unusual dam. If the dam is truly 16' high and 16' thick, it a very skinny dam. Ideally, it should be 3-4 times thicker than it is high.

When you stand below the front of the dam, is it really 16' high? If that's the case, it will probably eventually collapse. If less than 16', that means some of the 16' depth is below the ground. Only the part above the ground is counted as dam height, and has water pressure behind it.

A good quick fix for the bulge is to widen and heighten the dam at that point. A few loads of clay rich dirt can work wonders to stabilize it. Increasing the height is very important, as the weight greatly speeds up soil stabilization and compaction. Even 2 feet of extra height can work wonders until it's stabilized. Once stabilized you can even out the grade.

bobad #112219 03/20/08 05:45 PM
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Bobad, thanks for the response.

Sorry I didn't describe the dam clearly. It is 16' wide at the top of the dam and it does get much wider towards the base, it's roughly a 45 degree angle on the dry side and steeper on the water side. It holds about 16' of water from the base of the dam to the the bottom of the overflow pipes and it is about 4' higher than that to the top of the road. Because of the slope of the land, the dry side of the dam is at least 25' below the roadway. I like the idea of adding the clay to the area, although I would be a little concerned about driving the tractor over the area. I should probably wait until we have at least a week of dry weather. Should I also add bentonite to the water to help stop the leak from the other side?

Thanks,
Jeff

Jeff244 #112306 03/21/08 05:40 AM
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I doubt that bentonite would help. IMO, you have a structural defect and the gravel could be suspect. I can't think of anything to do but pump it out and take a look. If it blows on its own, you will lose the soil and flood the road.


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I am going to try to monitor the "bulges" (I think I found another one) by using a transit or with string lines. I can't do anything until summer because the pond would keep filling up from the rain. Although if there is substantial movement I will have too.

What does anyone think about after draining the pond, removing about 4' of dirt from the water side of the dam, add bentonite and replace it? I would also add an additional 3' or 4' of new dirt with bentonite to it.


Thanks,
Jeff

Jeff244 #112342 03/21/08 11:11 AM
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Can you post pics of the subject? Also, can you describe the bulge area and how it relates the wet zone (knock it off, Theo).

Brettski #112343 03/21/08 11:13 AM
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I just fell off my chair.


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It sounds like it would be wise to build a siphon over the dam and lower the water as much as possible before something catastrophic happens.




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Are you guys saying my dam is happy to see me? (sorry)

I took some pictures and I will attempt to post them later. You really can't see the bulge very well but at least you will see what the site looks like. The wettest area is just below the bulge. The bulged area starts about 8' to 10' below the top of the dam. Its easier to see where it ends because that is where it is more uneven.

Ryan, I am monitoring it very closely. We got about 10" of rain on Tue-Wed and the water is still coming out of the overflow pipes. If I notice anymore movement in the dam I will start to remove some water.

Jeff244 #112396 03/21/08 05:22 PM
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OK I opened a photobucket account and put a few pictures on it. Here it is: http://s291.photobucket.com/albums/ll286/7jeff22/
As I said, you really can't see the bulged area very well.


Jeff



Last edited by ewest; 03/21/08 07:58 PM.
Jeff244 #112399 03/21/08 05:47 PM
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Boy, that's a great lookin' pondsite. I really like it Jeff.
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Are you seeing a continuous trickle of water from any point of the damp area? In other words, there is alot of dam below the damp zone. Are you able to identify a trail of water moving along downhill from the damp area?
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Now, remember that this next thought comes from the guy that waits until the ice is 1.5" thick at the end of winter before he ventures out...
You say the bulging area is directly above the wet zone. Could a guy take a shovel and remove the grass in the area directly between the bulge and the damp area; maybe a 4' square? Then, lay down some plastic (to pile up soil) and do a little digging directly into the back of the dam....maybe 2 - 3 feet deep max to sample the soils and see what's goin' on.
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Any thoughts, you guys?

Brettski #112413 03/21/08 08:41 PM
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Nice looking dam. Sure hope it doesn't have a fault. I would sure be giving it a closer look per Brettski.


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Jeff,

The photos tell the story. That dam is way different than I pictured it.

Still not sure about the depth of the water behind the dam. If it's approaching 10 feet, the pressure is powerful and relentless. It will work 24/7 trying to escape and wash out the dam. If the 16' depth you mentioned is largely below the ground and the water at the dam is well under 10 feet, a repair may be possible without wrecking your nice dam.

Either way, drawing down the pond is inevitable, more or less.

bobad #112443 03/22/08 08:45 AM
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Jeff, if I were in your situation I would consult with a someone very experienced and knowledgeable with earthen dam structures. The money spent will be worth it to ensure that all repairs made are necessary and sufficient to safeguard the dam, the pond, and everything downstream from a potential washout. If I did not know someone who fit that bill locally, I would call in Mike Otto.

P.S. I think you have received good comments and info above, but there's only so much that can be done via pictures and descriptions. A pro on the spot can make a much, much better call.

P.P.S. As noted above, I strongly advise against heavy loads going over the dam until the bulge/wet zone problem is diagnosed and repaired.

Last edited by Theo Gallus; 03/22/08 08:48 AM.

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Thanks to everyone for the replies.

I am new to message boards so I apologize for not being able to figure out yet how to copy other posts to respond. Although my wife did show me how to post pictures.

Brettski, there doesn't appear to be any running water, but there are a few spots with some standing water and some mushy areas. I think I will wait a few more days for things to dry out and try digging a hole as you suggested.

Burgermeister, thanks, we really love the pond and had to wait 6 years for it to fill completely and I am hopeful that major reconstruction isn't needed. Also, we stocked the pond for the second time last year.

Bobad, I would guess that there is at least 12' of water at the dam. DW found some old photos taken at during construction and as soon as we can get to a Walgreen's we can have them converted to digital so I can post them.

Theo, I am thinking of calling the excavator that did the work for me. He made a point of telling me before construction that there was no guarantee that the pond would hold water. A lot of mining has been done in the area and it is known for large gravel deposits. I would like to accumulate as much knowledge as possible before talking to him. I will not allow any heavy loads over the dam until I am sure it is safe.

I've added a few pictures taken last summer when the water level was a lot lower to my photobook album. Here is one of them.

Thanks,
Jeff




Jeff244 #112855 03/25/08 04:14 PM
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I finally am able to post some pictures taken during the pond construction. I don't know much about dam construction, but I thought the guy did a good job. I will call him in the next day or so. If anyone notices anything out of the ordinary in the pictures, please let me know. There are a few more pictures on my photobook site also.

Thanks,
Jeff











Jeff244 #113034 03/26/08 12:49 PM
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Jeff,
I don't want to leave ya hangin', but I don't have alot more to add. The core looks good, except that it is difficult to tell if the overall length is sufficient...? What I do have to ask is the construction process I see. I will throw this one out for the other dirt guys on this forum. It appears that the dam was constructed, then the core was cut thru the new dam. It's not how my guy did it. I could be wrong, but this practice doesn't make sense when you consider that the best dam is continuous, layered monolithic structure. Is it just me?
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If you have the ability to reach out to the excavator that built it, and you think that he will have a reliable memory (?), do so. I would remind him of his proactive statement of disclaimer to hold water, then describe your findings at the back of the dam. It does appear in the '02 pics that there is a notable amount of rocks/gravel, but I don't have the experience to make a statement as to their relative detrimental value in a make/break equation.

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Brettski,

I agree about the dam construction method. I found a bunch more pictures but I can't tell for sure if thats the way it was done, although it does appear that way.

I called the guy who put the pond in and he said that he will stop out tomorrow morning to take a look..

Thanks,
Jeff

Jeff244 #113230 03/27/08 05:06 PM
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I am a geotechnical engineer and design and build ponds.
First off, the dam looks like its 25-30 tall, with steep side slopes. Unless you have very good material, that is pushing the limits of slope stability. I typically shoot for 1/2 slopes on the upstream and 1/3 slopes downstream. These yield a good factor of safety in most soils. Second, from the pictures the soil looks to be too dry as it is placed. This would not allow much compaction and would very likely results in seems in the core with a high potetial for seepage.

If this was my pond, I would drain it down to the level of the bulge, dig out the area of the buldge and see whats going on with the soils there. Find a soils engineer in your area. He can save you alot of heartburn.

John Schenne

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Jeff,

Not having any experience in dam construction, I would tend to side with Ryan, JAS and the others who have suggested to drain the pond, unless Depends makes an undergarment for leaky dams.

Just curious...what was involved with the mining core hole repair, mentioned in your first post?

Thanks

Russ

Last edited by Russ; 03/27/08 07:31 PM.
Russ #113417 03/28/08 07:49 PM
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John,

The dam is about 20' tall on the water side and a good 30' tall on the other side. According to the guy who put the pond in, the slopes are as you recommend, 1/2 on the water side and 1/3 on the other side. The dirt was definitely very dry when the work was done. There is also a high amount of gravel in the soil. The area below the bulge is wet and some small puddles can be seen in some indentations, like deer footprints. The wet area does not go down to the bottom of the dam, which is dry.

The excavator stopped out and looked at the dam. His recommendation is to keep an eye on the bulge and the wet area. He said adding bentonite to the water would not help. Maybe the bulge isn't as bad as I made it out to be. The pond is completely full and hasn't lost more than 1/2" in the last week, if any. We are supposed to get some heavy rain early next week so we'll see what happens.

Russ,

I wasn't there when the holes were repaired, but from what I was told, the holes( 2 or 3 of them) were either 4" or 6" in diameter. They dug out the areas a couple feet to make "wedges". They stuffed something in the bottom to support some concrete. They poured a foot or so of concrete and let it set. Then they added soil mixed with a high percentage of bentonite and added water. It did work. The one time the pond filled before fixing the holes, we lost a good 1.5' a day until the pond was about half full and it never maintained above that level. This is the first time the pond has stayed full since it was built in 2002. That is why I am reluctant to drain the pond again, although if I see any signs of the bulged area moving or the wet area actually starts to flow.

I appreciate all of the help I received. I wish I would of educated myself before starting the project.

Thanks,
Jeff

Jeff244 #113462 03/29/08 08:37 AM
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If you keep the pond drawn down, the rain will eventually help compact the soil. I've seen dams that were jelly-like from being built with dry soil that allowed seepage. After a few hard rains, they compacted nicely and became firm.


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