Exsiting water main needs a casing pipe

[MarshfieldTimC]

I have an existing 12-inch water main (buried 8 feet deep and in service) and need to install a casing pipe on this water main under a proposed at-grade railroad crossing.
One option is to shut down the water main, remove the existing ductile iron pipe, install a steel casing pipe, reinstall/insert the ductile iron pipe within the casing, reconnect the water main and place it back in service.
Is it possible/feasible to cut the casing pipe in half (the long way) and weld it around the water main pipe, in-place?
Has anyone attempted to resolve the situation by any other method?

 

[bimr]

Don't think that welding a casing pipe in place has ever been done.

Assuming the water main is already in service, you would be best served by installing a new water main with casing.

Sounds like somebody has made a huge mistake. Remove the old water main and have it mounted on a plaque for posterity.

 

[jgailla]

A hinged split face casing should be available, although I can't remember the manufacturer. It is hinged on one side and bolted on the other, basically like a long tapping saddle without the tee opening. I had a somewhat similar situation a few years ago.
I believe the cost was something like $80,000 for three 25 foot lengths of split casing.
If you can take the pipe out of service and replace it that is probably your best bet as bimr has noted.

 

[cvg]

welded or hinged, how would you install such a monstrosity? $1,100 per foot! New waterline would be just a fraction of this cost, maybe even if you jacked and bored.

Wouldn't it be a lot cheaper to install the new line next to the old one and then hot tap to connect?

 

[Zambo]

I think a bit more info would be useful.

Is this an existing railroad track that is in use and cannot be closed except for a few hours?

Is the water main also existing, crossing the railroad track at approximately 90 degrees and can also only be shutdown for a few hours?

In this case is it correct that it has now been decided to build a new road which requires a new at-grade crossing roughly along the alignment of the water main?

Then you have discovered that the water main has been installed without a casing pipe and either the railroad or the highway authority require the casing.

If the above assumptions are correct then it seems that cvg's suggestion would work well. Directionally drill to insert a new water main with casing in one pull. Then form pits and connect up to the old pipe.

 

[MarshfieldTimC]

Thanks for all the posts.
The situation here is that the railroad track is being extended, on a new alignment which will cross over the existing water main. The existing water main could be taken out of service if necessary. Seems like the best move here is to shut down the main and install a new casing and water main.
Thanks again!

 

[zdas04]

Not sure that really is the best solution. Since the train tracks are not there yet, it sounds like you can expose the water main without a major upset.

In that case, just cut your casing in half longitudinally, put the centralizers on the existing main, then tack weld the casing back together. It doesn't have to hold pressure, so I'd run a full length bead (to try to keep it a bit water tight), then put 5-6 6-inch tacks per joint. The costs will be, (1) exposing the pipe (must be done in either tack-on or line replacement); (2) cost of the casing (both cases); (3) cutting the casing (just tack on); (4) girth welds on the casing (both cases); (5) tack welding the longitudinal seams (just tack on); and (6) backfill and clean up (both). So you add cutting the casing and tacking it back together, a couple of thousand dollars. On the other hand to replace the line means taking it out of service, draining it, cutting out the section (maybe just on one end) and installing the casing without pushing all the centralizers to one end.

Split boots are probably not an option on the market, so you can either fill the casing with wax (which is a great solution in heavy traffic situations) or use something like a pond liner and making your own boots.

I don't know about you, but I think I would get a much better result by installing a split casing.

David

 

[bimr]

The method that you proposed (splitting the casing) would work. I would think that it would probably be easier to take the pipe out of service and reconstruct it. You should run it past a reliable local contractor for his opinion. After all the contractor is responsible for construction means and methods.

You should review your proposed method of construction with the railroad.

 

[sewerratt]

We've done this before when we've had to extend existing casings when roadways are widened. We split the encasement. Weld alignment 'ears' on the new edges. Dont use spiral weld casing, it will warp and make it difficult to get it back in shape. Uncover only 8-10' of pipe at a time. Install spacers. Work the half casing with ears under the pipe. Put the other half on and weld back. Backfill. Repeat until done.

It is a real pain, and not as effective as you'd hope, but our DOT requires it on widening. You'll have problems in the future removing the pipe from the casings (if that was one of the intentions) if the end welding wasnt perfect and the casing is misaligned or if the pipe wasnt laid perfectly straight. Plus you'll worry the whole time you have a significant portion of a main exposed that it'll move and leak or worse.

If you have the ability, and the main can be down for a while, lay an encased new one next to it, shutting down the main only long enough to connect the ends outside the RR ROW. Grout the old one. A new encased main will have a narrower trench which equals less load on a casing. Split encasement means a wider trench to make room for finicky welders and the space needed to fish the casing under the main. Wider trenches (positive projection embankment condition) equal higher loads on a patchwork welded casing with a long weld at the springline. Something to consider under a railroad.

A new parallel encased main is the best way to control the quality and keep it safe. And it should be cheaper. That is my experience.