Pond Boss Forums POND CONSTRUCTION Building a dam Back at it

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 ?????