Damaged pre-stressed ocean outfall pipe 2

[NADOR123]

Hi everyone

I am working on a project to stabilize an ocean outfall pipe ( 72 inch Dia.)constructed in 1980 and has cathodic protection system. A study has been completed by Pure Technologies to monitor the condition of the pre-stressed outfall pipe (section of the pipe about 2.5 miles under water) The recent results indicated that the section of the pipe in the water has a high number of wire breaks.



The outfall can not be shut dawn because there is no storage capacity in the waste-water treatment plant and temporary pipe(bypass)is not going to be allowed be environmental department besides the heavy boats traffic at the bay, therefore the slip-lining solution to stabilize the pipe is not considered. The pipe is buried about two feet below the bed level of the bay. The recommendation based on the high rate of wire breaking (717 wire breaks in 130 days) is to replace the outfall. We are trying to stabilize the pipe for the time being and until a new outfall is constructed. Any ideas about other restoration options!

Thank You

 

[Prepakt1]

Some suggestions
You could get a fiberglass or steel jacket made up in two pieces.Bolt them together around the pipe and grout if necessary.
What you need depends on the pressure differential. Fiberglass might need to be concrete wrapped. If so there are concrete mats that can be made up around the fiberglass.
If you are worried about internal blockage .Cut the section out and make the jacket overlap the gap.It may be possible to jet excavate around the pipe as its not too deep below the seabed.
If you cannot stop the flow, to reduce work time make the jacket hinged. Install the bottom part of the jacket, lift out the cut section and flip over the second half of the jacket and bolt.

Intrusion Prepakt /marineconcrete.com

 

[NADOR123]

Thank you for your helpful suggestions

Do you think jet grouting the soil around the pipe would work as it might stop the water from penetrating the concrete and cause the corrosion in the wires besides it would increase the pipe resistance to external pressure

 

[NADOR123]

I also forgot to include that the environment department has some concerns about excavating in the bay beside our concern of pipe bursting during excavation with flow running.

Thank you

 

[NADOR123]

I also forgot to include that the environment department has some concerns about excavating in the bay beside our concern of pipe bursting during excavation with flow running.

Thank you

 

[Prepakt1]

Depends on the surrounding material. You can always grout, but the surrounding material might not let it permeate around the pipe.This will reduce or eliminate the ability of sea water to corrode but will not do much structurally. To strengthen you need to excavate. If the pipe is open at the end,the pressure differential should not be too high. You say the pipe is 2.5 miles deep that seems a bit unusual.

Intrusion Prepakt /marineconcrete.com

 

[NADOR123]

Thanks

The pipe is 2 feet deep below the seabed and the length of the pipe underwater (the bay section) is about 2.5 miles.

 

[Prepakt1]

If it becomes necessary to excavate,the best method is to build an oversize jacket in two parts. Leave about 4 in clearance between the steel and concrete at the damaged area to provide cutting space.Provide a top flap longer and wider than the section to be removed or repaired. You can close the flap with built in hydraulics. You can then work on cutting out or repairing the damage with no concern about a long term leak while you are working.You can always seal it up at any time or between operations. This type of work always has delays.

Intrusion Prepakt /marineconcrete.com

 

[NADOR123]

Thanks

Do you think jet excavation would be the best option to install the jacket and without causing other problems in the bay.

 

[Prepakt1]

Ask some of the local diving companies they will know what equipment isnecessary to excavate the local seabed . Which bay are we talking about.

Intrusion Prepakt /marineconcrete.com

 

[NADOR123]

I am talking about the South Bay in Suffolk County( long Island ) New York.

 

[StephenA]

You could also use a dredge pump hung off a crane on a barge to excavate around the pipe. We use 10" Toyo pumps but there are other makes including some with agitators. It will depend on what the original trench was backfilled with.

If it is a short term solution that is needed and assuming that the concrete is still intact, then steel jackets or bands tightened around the pipe could replace the broken wires as reinforcement.

Stephen Argles
Land & Marine

http://www.landandmarine.com