Pipe Bursting Underneath Electrical Building 1

[FernDogg]

We are having problems with an existing 6" concrete sewer force main in an RV Park. The concrete main is in need of rehabilitation. We would like to Pipe Burst the main and replace it with a 6" HDPE line. But The problem with the existing main is that it travels directly underneath an electrical tranformer and an electrical utility building. The existing force main also lies in the same trench with a 12.o KV Conductor Line. We ruled out the Open Trench method to route around the transformer because the RV Park has several other utilites running running through it and there are no Utility Maps for the Park. Has anybody had a bad experience from a pipe that was laid through pipe bursting and the pipe suffered a break or a leak? And does anybody know if the Pipe Bursting method will disrupt the existing electrical line going to the transformer? Would electromagnetic logging help to avoid the electrical line? Thanks everybody for your input.

 

[dicksewerrat]

Do you know how far away both vertically and horizontally the elec. line is? Pipe bursting works well but it will displace the soil around the pipe. Can you down size to 5"? You will have to dig up the ends of the force main. If you are running it with a decent pressure head, you may be able to directional drill it. Is the 12 kV line oil filled?

 

[FernDogg]

We know horizontally where the electrical line is located but not vertically and the line is not oil filled. Reducing the line size is not an option.

 

[dicksewerrat]

If the conduit is more than 2 feet away you should be ok. I would dig up the pipe and conduit, then test the soil between them to see if it can take more compaction. You will be pushing the old pipe out and away to aloow for the new pipe. Are there knowledgeable contractors near you? You can spec the new pipe so you should have no problems. Once you have the two pipes exposed is when to call the contractors for bids. Require them to visit the site before submitting bid.

 

[FernDogg]

Thanks for the tips, dicksewerrat! I will definitely bring it up when I submit the plans.

 

[KRSServices]

You have a concrete forcemain? Cool! Thats a new one to me. Are you sure that it is a forcemain?

Is it possible to relocate the sewer line? You mentioned that a utility building and the trasformer were allowed to be constructed on top of the existing line. As with excavations in existing urban areas or existing high density residential developments, care is going to be needed to undertake the work, but cable, phone and electrical are relatively easy to locate. Water sewer and gas, are a little tougher, but an experienced contractor and project manager should ba able to complete the work without any catastropies.





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[vicman2]

Krsservices is on the right track. Relocation will provide the best long term solution. Perhaps you should consider hand digging near and around the electrical conduits. The transformer will have a ground system around it. I will be a combination of ground rods and cables about 1 meter out from the base of the transformer. Depth will depend on the conductivity of the soil. Directional boring is an option, however the drill head will follow the path of least resistance, usually an existing trench. Pipe bursting should work as well. The force main and electrical conduit are probably bedded in sand and should allow for some disturbance. A simple procedure for checking for electrical conduit damage is to isolate the electrical conduit at either side of the transformer and either fill with water or pressure with air, if water level drops or air pressure drops, them you have damaged the electrical conduit. Any work you do around a 12kv line should be done with the power disconnected. I am assuming that the line is in a plastic conduit of some sort. Hand digging is not as expensive a you might think. Most electrical lines are only 4 to 7 feet deep.

 

[dicksewerrat]

I was mulling over your problem some more. How far is it from the pump station to the outfall of the force main? where it goes to gravity flow. How much pressure on the line? You may be able to line the concrete line by the CIPP method.

 

[FernDogg]

We will replace about 400 ft of force main. CIPP was considered but I'm afraid that it would reduce the diameter of the force main significantly and drive up the TDH. If you know of a good contractor or manufacturer that is involved in CIPP please contact me.

 

[dicksewerrat]

Go to my public profile and email me. I will contact you after that.

 

[FernDogg]

The City I am working for is still skeptical about pipe bursting. They say its a viable option but it can cause a perception problem among the City's residents. I can understand that the typical resident can get a little bit frightened by the thought of bursted asbestos pipe fragments in the ground but as long as the asbestos is not friable there won't be a problem. I promised the City I would look into other alternatives. I researched CIPP but the industry reps tell me they would not use it on a pressure situation like my situation. They told me I can't transition it to other pipe material as easily. One rep did tell me to check out DuraLiner. DuraLiner is used for pressure pipes and can withstand 150 psi and can be used with ductile iron fittings and also has a life of 100 years. The problem I see with Dura Liner is that since its made out of PVC the wall thickness can be huge enough to increase my TDH. Does anyone know the thickness for a 6" max outside diameter of Dura Liner? And at the elbows I have in my host pipe will have to be point repaired. Is this a real alternative to the pipe bursting? Hey sewerrat this is my email: fduenas@psomas.com

 

[KRSServices]

Ferndogg,

Thank you for the clarification, I now understand that the existing pipe is AC (asbestos cement), rather than a concrete pipe or mortar lined pipe.

The propblem with the liner is that the I.D. will be reduced. You have to calculate the differences in capacity and the flow hydraulics to determine whether that option is acceptable or not.

I would still look to see whether another alignment is possible because I am not comfortable with permanent structures (a building) creating a hinderance and liability should a leak result in a repair necessary under the offending stucture. Have you looked at horizontal augering as an option? It is expensive, but is pretty much trenchless.


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