So I have been working between rainstorms this fall to do a pond expansion and change the overflow system from waterfall to structure

From This

To This

And

From This

To This

For those of you that remember my posts from last November/December .. The pond filled great .. held water, and did everything it was supposed to do and more .. The water pressure pushed the springs back and created water pockets because the water had nowhere to go, which is the reason for the expansion .. The digging was tortourous

Gave me lots of flat stone to line the sides with

Like this

If mother nature would give me a few more days of nice weather I would do some finish work and then button it up for the winter .. Windmill arrives in 3 days from Ohio .. pad is poured and water is waiting for some aeration

And here are a couple pics from late spring .. the dogs loved the water

Have some dry weather going on so took the day off and worked on the pond .. no sooner did i get here to check on things this morning when the seal around the pipe at the bottom of the concrete structure lets loose .. a fairly minor setback but really strange it did it the moment I got there .. the pond will drain .. AGAIN .. I will fix the seal ..
All is not lost .. my windmill will be put together by the time the pond is drained so I will be able to place the air stones exactly where I want them

Well Mike, better now than 2 years from now! I think you'll have another day or 2 of good weather.

A real show place.

Great to see you back on the forum, Mike! Can't wait to see the finished product. Again.

Well heres a puzzling one .. I set a 11,500 lb. cement structure at the foot of my dam .. connected it with a seal specifically designed for that application .. a couple of days ago as the pond was filling for the first time since the structure was set and I believe I encounter a bouyancy problem .. the 11,500 lb. structure shifted and the seal was comprimised .. the pond was only about 2/3 full
I never considered that the huge cylinder would become bouyant .. Ill try to post some pics

Mike,

Sorry you're still having problems on your beautiful pond. Hope you get everything worked out.

I had a waterfall idea similar to yours (but on a bigger scale) for my land. Why are you bypassing the waterfall?

This is the base of the structure which was connected to the discharge pipe

Structure going in

THAT big s.o.b. floated???

And the finished product



I spoke to the precast company that made the structure for me and they cannot believe it moved .. but it did .. and I believe it moved because of the pressure of the water ..

Any thoughts ?? Or better yet .. Any Solutions ??

From the top

I know right .. yes in a sense it did .. the precast company has suggested pinning the stucture to the pad it sits on or pouring concrete around the base essentially anchoring it to the pad below.

Mike:

What are the inside dimensions (hollow area) of the structure? I.D. and length?

I worked on a floating pier in San Diego Bay that developed cracks in it and was leaking. It was actually a 4 lane highway that was made of concrete that was hollow in the center, and it was towed down from the State of Washington. The cracks developed while it was being towed to SD. So, yes, I believe it floated.

Mike, if you can get the inside dimensions, you can figure it out yourself. One cubic foot of air will float 62 pounds. Or post the dimensions and I can do it.

Esshup .. Great info as always on this site .. the inside diameter is 48" the height is 129" .. keep in mind though (and I'm not sure that this makes a difference) that the there is a hole in the bottom to accomodate the 24" discharge pipe .. I originally, mistakenly, thought that this would equalize the pressure .. Obviously I was incorrect but I would imagine that it has some bearing on the calculation ..

FishinRod .. I scrapped the waterfall design because water travels the path of least resistance and can be diverted with a leaf .. and when water is diverted so goes the sub-base .. and once the erosion started the problem magnified times 1000 .. if 5% of the water going over the falls diverted behind one of the stones toward the top of the dam .. eventually the base became saturated which in turn softened the base structure which allowed for settling which changed the pitch of the rock which allowed more water to veer off course .. and so on and so on ..

Mike, on a quick calc, the area (air) in the pipe will float 8375 pounds.

So, unless there is more volume of air somewhere that is contributing to the lifting forces, or the concrete pipe doesn't weigh what you think it weighs, something isn't adding up.

Well .. hmmmm .. (scratching my bald head) .. I dunno

Thank you for the info Esshup .. something moved that structure .. if it wasn't water pressure .. do you or anyone else have any thoughts as to what may have moved it ??

I think my only solution is to add heft with stability .. I will order up 3 more yards of concrete, pin it with rebar and pour the SOB in place .. a yard of concrete I beleive weighs 2000 lbs... I will then cable and turnbuckle the top structure to the rebar just for good measure .. that should hold her ..

was it in there during last year's freeze? Ice floe?

no sir .. just put it in two weeks ago

Mike,

Thanks for the waterfall info, that's what I was afraid would happen on my project.

It looks like the water should just go straight downhill on your waterfall. Do you think a pond liner, then a sand buffer, then geotextile, then topped with the ledge rocks would have worked on your waterfall?

Im sure there is a way .. I thought that with enough of a forward pitch to the rocks the water would have to flow correctly .. but the spring thaws took their toll on the sub-base .. there was sooooooo much water pouring over the rocks that inevitably the water got around the edges and that was the beginning of the end ..

Mike, unless the total structure, including the drain pipe was completely sealed....there was no bouyancy. If the outflow pipe was exposed to air (below the lowest water level), water pressure would push against your structure attempting to flow out and fill the air space.

Think of an empty cup in water...sealed, it floats. Add a tube at the bottom of that cup that exits the water below the water level and that cup will sink from it's own weight.

If the outflow pipe rose as a supply line that exited above the high water level, then yes, the structure would become bouyant.

mike,

i might be able to help some i hope. i have installed a lot of manholes in floodplain areas and will share some simple formulas off a old set of plans i have. step 1) weight of pipe which 48" 4" thick is 683 lbs per linear ft. step 2) weight of water displaced which is 1069 lbs per linear ft. so for example at 10' deep pipe weight is 6,380 lbs and displaced water weight is 10,690 lbs leaving you with a upward force of 3,860 lbs or almost 40 lbs per ft. these figures were used with backfill all around the pipe. concrete does not weigh as much under water as it does in air. dont ask me why but more than one engineer has told me that so not using backfill around the pipe increases your upward force drastically. i didnt figure the weight of your concrete base because i dont know it but i can tell you the exact setup your using with dirt all around it will float if the groundwater is high enough because they make us mechanically anchor them. i think you need lots of weight to make this work and it needs to somehow become one piece not sections. the turnbuckle from top section to anchor point like u mentioned may work. they make us pour concrete collars.

i looked back at a retention pond we done several years ago. it has a 4' tall 48" concrete pipe with a 24" tube leaving it. it had a 1' thick 6x6 base and was set up just like the metal pipe on the thread building a easy pond i thought. so i know this set up wont float but 1' thick base adds a lot of weight

father in law says you cut the weight of concrete almost in half when you submerge it.

Tim:

Thanks for the info. That explains it! More good information to file away.

essup on a different subject i got that 23 acre pond done but the owner wants to post it. it is a dandy with several hundred ft of roadway and a cul-d-sac built out in the pond he should post it here pretty quick. i showed my father-in-law a picture of the structure in this pond because he has installed manholes the last 43 years on a daily basis. he said that he had never seen that done or tried but that it would take a lot of weight to secure it and he also said to make sure and somehow secure the hdpe where it exits the manhole or it will vibrate and crack the hdpe in a very short period of time

Had a perfect day to erect the windmill .. other than very cold .. couldn't have asked for a better day .. now the pond gets oxygen ..with all the above ground springs feeding the pond I'm not sure if it was necessary .. but since wind is free I just had the initial expense and maintenance from here on out . I will post pics soon

Mike,

I was looking at your pictures of your concrete outlet structure. It looks like that you have is set on a concrete slab. How thick is the slab? Could a slab failure be the cause the shift in your structure. Even if the slab did not fail there could there be soil settlement, compaction?

The foundation slabs are very important to the stablity of the outlet structure.

Herb

Hi Herb .. And thank you all for your responses .. I excavated down to a solid sub base consisting of some huge native boulders (which are very prominant on my property) and poured approximately 5 yards of concrete so Im pretty sure the pad didn't fail as the strucure is still perfectly level .. On further inspection, I'm fairly certain the stucture became bouyant .. I'm not sure why or how but it did ... the position of the stucture moved forward about 5 inches, comprimising the seal and the rest is history .. I decided that the new structure position and allignment are ok to reseal it where it is ..
Now I wait for either a stretch of dry weather or a hard freeze so I can get a concrete truck backed in to pour 5 more yards of concrete to anchor it in place .. Im going to drill and pin the fresh concrete with rebar to the existing 5 yard pad and cover the flat base of the sturcture .. when the fresh concrete sets I will place a couple of large boulders on the top of the newly poured concrete for good measure. The only real consideration with this plan is .. ITS PERMANANT .. I could Jackhammer it out if need be .. but for all intents and purposes .. Its there to stay .. Any thoughts ?????