Buried ductile iron pipe - how many feet in one connection?

[s0eebuch]

All,

One of my local clients has hired my firm to design a waterline replacement project. About 3,000 LF of transite pipe to be replaced with 6-in diameter ductile iron.

At the tie-ins (where the DI meets existing pipe) I am specifying solid sleeve cast couplings (smith-blair or equivalent).

Obviously the proposed water line cannot sit in the same trench as the existing transite. Plus, because the shutdown to make the interconnections must be as short a duration as possible, I must limit the amount of pipe to be installed while the system is offline.

So, my question is this - I show two 45deg. horizontal offsets to meet the existing water line to tie into, but how much pipe can I indicate for the contractor to replace during one shutdown period (usually less than 8 hours)?

I figured around 3 sticks of pipe (at 20 foot long each) for 6-inch diameter pipe is max. But another engineer here has indicated that the contractor would be good if he can get just one stick in the ground and connected.

Anyone have any experience with waterline replacement? The majority of the proposed water line will be in a separate trench along the road RoW away from the transite pipe to be abandoned - but these interconnects are giving me issues.

Thanks.

Ed

 

[SteveWag]

In central PA (USA) we see a utility contractor place 200 to 300 feet of 6 – 12 inch waterline a day, average, no rock. I would, without a better understanding of the job, figure laying ALL of the main parallel to the existing, no shutdowns. The danger is that the Transite may be damaged if it disturbed. Then I would install valves at each end and test and disinfect, keeping in mind thrust restraint. Then with one 8-hour shut down I would shut down and connect at both ends. But first, I would expose the Transite at each end and get a good diameter measurement, some of that stuff was pretty sloppy, and machined only enough to shove into a bell. You may use one machined end but I usually plan on two un-machined ends.
Steve

 

[s0eebuch]

Steve,

My thoughts exactly but the connection to the existing water main is at an end connection (longitudinal axis of the pipes match end-for-end).

With that, I need to eventually use some sort of coupling - meaning the pipe will have to sit in the same trench as the existing pipe in order to line up and mate together.

...geez, I need to post a plan sheet.....

I hope this is making sense.

Although, I am relieved to see that the contractor should be able to install my 60-foot connection during one shutdown period.

We do not encounter rock here in central Virginia either - well, not normally. Some parts in "Southside" have surprised us.

Thanks!

 

[coloeng]

If the new DI pipe can not sit in the same trench as the AC pipe, why can't the contractor install the entire 3,000 ft before doing a tie in as SteveWag suggests?

We typically use a Maxi-step Dresser coupling to connect between DI or C900 and AC pipe. A solid sleeve may work on 6-inch AC, as it is typically the same OD as DI. On larger sizes of AC a solid sleeve typically won't work because the AC has a larger OD.

 

[bimr]

Why are you not using 8 inch pipe? 8 inch pipe is generally the minimum size for municipal installations.

In addition, every time you put a new section in, you will have to disinfect the new section. That does not make any sense and will waste lots of time.

You should intall the entire section and then disinfect it. Then go back and install the services while the new section is pressurized.

Use hot taps as necessary to minimize downtime on the existing system.

 

[s0eebuch]

Perhaps I haven't explained myself well.

The majority of the 3,000LF will be installed in a separate (parallel) trench.

My question concerns the tie-ins.

I would prefer not to tie in to the existing pipe at 90 degrees because then I'll need some very large thrust blocks.

Most of the 3K LF of proposed waterline will be installed and disinfected well before shutdown occurs.

Again, my question concerns tie-ins only.

The diameter of pipe was at the request of the client.

At some point along the parallel installation, I need to tie into the existing waterline. How long should that "replacement" or tie-in section be? That's the question.

Thanks to all who've responded.

 

[bimr]

The minimum separation distance between the water mains should be around 5 feet. That will allow you to make the taps at a later time without the old pipe being in the way.

Do not bother with thrust blocks. Use all restrained joints on the piping tie-ins.

http://www.ebaa.com/

You do not have to use a 45 degree joint. A 90 degree joint would also work. Again, do not bother with thrust blocks.

The replacement piece needs to be only 5 feet long. Think about installing tees on the old piping and then capping the transite end of the tee at the end of the project.

You will also have to restrain the old pipe where you are making the tie-ins.

You should also recommend 8 inch pipe to the owner.