Designing a Precast Concrete Inverted Siphon

Oops; I'm sorry I looked.

Was interesting right up to:

Due to the unpredictable weather pattern attributed to climate change

Weather has always been fairly unpredictable and this new type of unpredictabilty is off my range.

in the statement "due to unpredictable weather pattern attributed to climate change" refers to the jobsite where we are going to construct the siphon that's why we choose to construct the siphon by precasting rather than cast in place. Well at any rate I have initially drafted a uniform pre-cast section of 2meters lenghts using an insert on hooked plate and snap on then welded steel plat at sides and top of barrel with inserted rubber square flap at inside of the joined barrel.

I'm passing on this one as well.......scary thoughts entered my brain as I read the OP.

Good luck on your project!

Every one seems to be running scared. I'm not an engineer so the numbers don't frighten me as easily. ... Why not use an alternate material like a plastic resin or some sort of fiber filled concrete. And why bolt it together when there are ways to 'snap' fit pipe sections. (insert one end into another & backfill connection gap through small holes with an injected sealant, better seal & less susceptable to movement/shifting trouble) ... Maybe create an 'in the ground' (open) section of pipe & then 'cap' it with a 'lid' or upper pipe section- using tar or some other foam type fill to seal the top to the bottom? I could come up with more but (your patience &) my time is limited. Thanks & good luck. Carlos

Hello Guest

What liquid are you trying to syphon. If it is water, 12 meters will not be possible. The practical maximum with water will be considerably less than the theoretical 9.2 meters max. Things you will need to know are; minimum atmospheric pressure (affected by altitude, vapour pressure of liquid to be syphoned, density of liquid). I have no experience building concrete syphons other than low head on sewage systems and I could purchase them pre-made. I think if you make sure all joints are sealed and you can start the syphon (possibly by pump), a simple design will work with no hidden crevices or pocket joints. Watch out for gas bubbles if you are close to the maximum syphon head...they will stop the syphon. It sounds expensive so be careful and seek professional help. What is climate change variances that you expect?

Guest, by "reverse siphon", do you mean an "Anti-Siphon"? That is to say, a big "U-tube" which will go under an obstacle such as a ravine or a road?

The guys on this forum could design that in their sleep, providing you give them some more information....like what is the soil type, what is the weather you are worried about, are there any gates which might need to be built or considered, and maybe provision for fish or other wildlife.

I am assume that, by unpredictable weather, you are referring to the possibility that the probably maximum storm event might be exceeded. If the opposite event occurs (i.e. drought) then your design will in fact be overdesigned. But that is the subject of another discussion.

Because you are the designer, I think you can specify the manufacturing of a steel seating plate. I do not think there is a market ready steel plate for this type application. Any fabricator could make the plates. In addition, they could probably provide better information than I am.

By using bolts to connect concrete sections, you will create stress points at the bolt locations. The intent of the plates is to spread the load about a concrete bearing surface to prevent localized shear failure in the concrete. If the steel will be exposed for the life of the project would think that steel types A242 or A588 (AISC Specifications) would be preferred for the steel seating plate designs. If you use any other type of steel, I recommend that it be galvanized as a minimum. However, I would recommend that the bolts be recessed in a pocket with the bearing plate. I recommend testing on the tension in the bolts. Once the bolts have met tension requirements I would grout the pockets solid. covering, bolt, nut, plate, and washers so that future corrosion would be very unlikley.

Because of your predicted head, I would recommend that any change in the alignment of the inverted syphon should include the design and construction of some type of thrust restraint bearing against virgin undisturbed soil. If that is not possible, the bearing should be against a pile(s).

However, that is a lot of bolted connections. That is, this sounds very labor intensive. Would post tensioning be acceptable for your intent? Instead of making a square structure, if you made it circular, you sould seal the inside seams with a rubber like seal. Movement in the sypon might be prevented by the friction of the earth. If not, a "anti-seep collar" could be constructed that is designed to anchor the sypon in the adjacent soil. It would be cheaper to do that than to bolt all the concrete sections together.

Anyways, I hope I partially answered your questions.