Underwater Intake Structure

[damengr11]

I have kind of a unique problem. We are doing a feasibility study of constructing a new intake structure for a reservoir. However, the owner really doesn't want to have to drain the reservoir so that we can build the new intake structure (for various reasons). Does anyone have any experience with constructing new intake structures under 50-100 feet of water? If so, how'd you do it?

Thanks for your time!

 

[civilperson]

Cofferdam the area to build in.

 

[damengr11]

Cofferdam that deep? I haven't seen one that deep. What do they use to construct oil rigs out in the ocean?

 

[COEngineeer]

I dont have the experience but my old man owns a sea water intake construction company in asia. Typically what he does he uses a prefabricated steel intake head and lower it with a barge.

Check out his company to see pictures.

http://www.swijetty.com

Never, but never question engineer's judgement

 

[COEngineeer]

it can also be precast concrete of course.

Never, but never question engineer's judgement

 

[JedClampett]

You drill a vertical access shaft. From there you drill horizontally under the sloped bank of the reservoir. From a barge, you have someone drill throught the bank into the horizonral access shaft.
Alternatively, you could precast a shaft on the shore with a bottom, float it to the correct spot and sink it at the location of you horizontal shaft. Then either excavate with a clamshell or drill until you meet the horizontal.
I'd be worried about the water quality unless you have intakes at several levels.

 

[msquared48]

I assume from your post you have a 50 foot drawdown during the winter?

The only way I see is cofferdamming the opening. How would precast work in a rock opening for the inlet structure - and the face would have to be scaled too for bond and stability - Underwater? Needs to be dried - vertical beam-columns with struts to the hillside as required and sheeting to close - should be able to do this.



Mike McCann
McCann Engineering

 

[Ussuri]

What do they use to construct oil rigs out in the ocean?

Well for ones that sit on the bottom, in shallow water up to say 200m, if steel, they are fabricated on land typically on their side then loaded onto a barge floated out to location and then up ended. If concrete (Condeep type), they are typically fabricated in a large dry dock then floated out to position and 'sunk' into place.

 

[BarryEng]

To damengr11
I have the same problem. We have a dam that is 50 m deep with an existing control tower (wet tower with an internal operating gate). The control tower does not have an access bridge (it was used as an irrigation dam only). The utility wants to use the water for 'normal' water supply & requires to drain the dam over 2 years to allow the construction of a new intake tower (with multiple intakes for water supply), but in the two years req'd to drain, they want to take 'run of river' water to a WTW (from the upper levels of the storage).

One proposal we are looking at, is to remove the trash rack (using divers of course), & place a transition piece in its place & then connect on a 1000 mm PE pipe. This pipe will be terminated with a 'strainer' & will be located (tethered) with a float & anchors.

One of the original suggestions was to use a caisson & construct the intake within the structure. We probably will be using the existing infrastructure (different to your problem) & I will be very interested to see what other suggestions you receive to your problem.

 

[Prepakt1]

It should be possible to pour a concrete intake underwater.
You need to make a steel mesh formwork and then fill if by pouring concrete into fabriform bags which will fill the formwork forming the shape of the steel mesh.

Intrusion Prepakt /marineconcrete.com

 

[bimr]

Why do you have to build under 50 feet of water?

If you have no boats in the reservoir, you can use a floating intake.

Otherwise you should follow COEngineeer's tip. Microtunnel from the embankment to the location of the intake. Then install a prefabricated intake using divers.

 

[crkdg]

I know question had been around a couple of months, but it sounds interesting and here is my input.

I could think of a bunch of ways to do an intake, but to me the bigger issue is how you are going to handle conveyance. How is the water going to go from the intake through the dam? I assume there is a dam of some sort. How much water are you talking about? How far below minimum pool do you need to withdraw the water? If it is pump driven, you should be able to do some kind of prefab intake and sink or drive it into place and run the lines over the dam, or maybe run them through the dam above your low water line.

I am used to big stuff, we would cofferdam (yes you can build high cofferdams) and do everything in the dry. If you had to do it underwater and it was pretty big and gravity driven, I would tunnel a regulating outlet through a solid embankment, build a gate chamber with rock trap, then tunnel the intake mouth close to the reservoir and do a wet tap. If you need trash racks, build an intake and sink it in place over the new inlet. Very expensive, twould be a lot cheaper to just drain the reservoir.

Again, the solution would really depend on how much flow we are talking about.

 

[rconner]

What size intake is required?

 

[civilperson]

An intake for temporary use could be a siphon made out of HDPE with the intake elevation at any level desired.

 

[gerhardl]

I have not seen any cofferdamming out in the North Sea or elswere for pumping oil and gas up, and mud and CO2 down. ( ;-) )

Build what you need on land and drop it controlled to the bottom from a barge or fleet, technology and advice available from offshore engineers, but also from civil engineer consultants, at least in Scandinavia.

Hight (dept) of pipeline intake to be controlled from weight at bottom and pipe up, or anchor weights at bottom and chains at proper length to pipe with floats.

Pipe in plastic most commonly used.

Where are the necessary engineering facts, like flow, dimensions and requirements else?

Elevation and necessity to go through geological structures or dams?

Pumping or natural fall?

Life expectation required?

... etc, etc.