Connecting pipes of different material

[SHOchris]

I have a 24" line that I am running under a creek. under the creek, i am required to use DI. I want to tie in to a 24" line that is 949_PVC on the other side of the creekbed.


TCEQ (Texas Commission on Environmental Quality) madates that a manhole be used when changing direction or moving laterally...but doesnt say you must use one if changing materials. I am wondering if I need to put a manhole there, or can i just put a fitting there to make it work and be ok?

TIA, Chris

 

[cvg]

the purpose of a manhole is for inspection or maintenance. Manholes are usually required for pipe size changes which may occur with different pipe materials. So if you are OK without being able to inspect this fitting and you don't feel that the line will clog at this point requiring maintenance and your pipe doesn't change size - then go without the manhole.

However, for a sewerline crossing a creek, I would suggest manhole on both sides.

 

[SHOchris]

thats more of what i feel comfortable with, but at this point....it seems that other people's main goal is to do this job with as little added cost as possible...within code,

 

[tnboy82]

Is this a watermain, sewer forcemain, or gravity sewer main?

If it is a pressuized main, then a manhole would be out of the question (assuming of course that you are using the manhole to compensate for different pipe ODs).

If the PVC OD is equivalent to the ductile iron pipe OD (I apologize for my ignorance, I've never seen the designation 949 PVC or I might be of more help). Then a ductile iron mechanical joint sleeve (or any ductile iron fitting) used in combination with MJ restraining systems (such as EBAA Iron Megalugs or Sigma One-Loks) are often used, but be aware that different models of retainer glands are use for the PVC and ductile iron pipes.

If the PVC OD is not-equivalent to the ductile iron OD, then a transition sleeve may be required to transition the ODs, these sleeves are available through most manufaturers such as EBAA Iron, Smith-Blair, Dress, Romac, etc.

There are other options, but those are the ones that I see most commonly.

And please, please check local codes and specifications for your area, as they often have requirements for these types of transitions.

 

[SHOchris]

The local codes do not require one, i have checked those very thoroughly. The TCEQ does not require one either, but i recommended to put a manhole there and we will see where that goes.

tnboy, i apologize for my own ignorance...the 949 PVC pipe may not be a real designation, that is just what the plans had written on them.

New problem with this though is that the surveyors we hired said the creek we were crossing was only 6 ft deep and it turned out to be about 15.... now the flowline of the pipe pretty much matches the creek flowline. The bottom of the DI pipe is only about 2 inches off the creekbed. I have been looking for a full day now in EPA and contract documents to see what I am allowed to do and have no idea...
any ideas?

 

[SHOchris]

and sorry, its a gravity sewer

 

[tnboy82]

Since it is a gravity sewer, then that both helps and hurts I guess. A manhole would be acceptable in that instance. My question would be if it is possible to use a manhole, due to elevation requirements (ie do you have enough elevation change between where the ductile iron pipe exits from under the creek to where your next manhole is located give you enough length and vertical distance to maintain grade required between manholes).

A sleeve would also still be a viable option (and I would think a more cost effective option, the price of excavating placing and grouting a manhole versus installing a sleeve). Whether it is a transition sleeve (for differing ODs) or a standard mj sleeve (for matching ODs).

Back to the PVC notation, I know much more about ductile iron pipe than pvc pipe, but I do know that C900 & C905 PVC ODs do match the ODs for ductile iron (and often ductile iron MJ fittings are used to with this PVC pipe).

 

[SHOchris]

Thanks, talking it over with one of the bosses, i think that we are going to put a manhole on the other side of the creek.
I am spec'ing to reinforce the embankments, and then encase the DI pipe in another steel pipe because there will be a joint exposed (code spec'd)....it is going to raise the water level about 2.5 feet right there, so I then plan to cover this in gravel, letting the natural flow cover it in silt and keep from creating a giant erosion hole on the downstream side of the pipe
sound like a winner?..anything i am missing?

"Don't worry about the world coming to an end today. It's already tomorrow in Australia."
---Charles Schulz
"Beer is living proof that God loves us and wants us to be happy."
---Benjamin Franklin

 

[cvg]

you are running the casing pipe above the bed of the river? You had better check with the floodplain manager about raising the water level. you will need a permit to do this and I would not be surprised if the permit requires to go under the river bed to below the estimated scour depth. Covering with gravel or silt will not prevent your giant erosion hole.

 

[rconner]

Unless more is known than what is shown here it could eventually become at least a little unsettling to someone (when they think about) that the creek apparently was originally at some point thought/found then? to be 6 feet deep at this location, and the bottom/elevation is apparently now 15 feet deep. They might ask the followup question, what will happen to the pipeline if the basic bottom condition of the creek itself somehow (through extreme erosion?) becomes say 24 feet deep/bottom elevation a few years down the road? I guess this sort of thinking may be why some folks sometimes go to deeper inverted siphons at such locations to provide for such. If that is done, I should note some thinking may also need to be done e.g. for some more frequent cleaning/mainenance issues associated with siphons. Ductile iron double barrel siphons are often used (maybe sometimes also with smaller sized pipes than the main line) e.g. for redundancy and/or to increase cleansing velocity in th emost often utilized brqanch etc.)

 

[rconner]

Oops (I should have said "siphons with two or more barrels"!)

 

[SHOchris]

well, the depth change has more to do with a terrible survey. in most cases, they were off by about a foot, but it was close engough for us to use this time, and find a new surveyor. It hasnt eroded away or anything... i think that the surveyors just didt want to get wet....

what are some good ideas for enbankment support, i was thinking something along the lines of a concrete winged structure around the pipe....

"Don't worry about the world coming to an end today. It's already tomorrow in Australia."
---Charles Schulz
"Beer is living proof that God loves us and wants us to be happy."
---Benjamin Franklin