Running Ductile iron water pipes under highways 2

[JohnWeal]

Good Afternoon,

We are making several crossings under a few highways.

The highways are dual carriageway so quite wide.

The pipelines are carrying potable water in ductile iron cement-lined material from 800mm to 1600mm.

Is it normal to change the pipe material to HDPE and use a steel casing?

As the ductile iron is buried, up to the crossing area we are using the push-fit spigot socket joints. So could the DI pipe be flanged under the roads?

Any advice appreciated and whether there are any preferred methods of doing this in accordance with AWWA etc.

Best Regards

John

 

[cvg]

HDPE is rarely used for potable water in the US. Flanged pipe is not common or recommended for buried service, use mechanical joint restraint such as megalug.
in most city and county arterial roadways, DIP or steel pipe is commonly used, with or without joint restraint as necessary.
under state or federal highways, usually in a steel casing.
AWWA does not have any requirements for highway crossings that I am aware of, this is a highway department requirement

 

[rconner]

Ductile iron pipe has been used for more than a half century, both uncased or cased, for highway crossings. The many pros and cons of cased vs uncased pipeline crossings, were discussed to some extent generic re all piping materials, in ASCE MOP No. 89, "Pipeline Crossings" in 1996.
While I think it is more common for many ductile iron piping installations of substantial highways such as USA Interstates to be of the casing carrier pipe-type, I have seen some in fairly recent years installed uncased. Some guidance for USA ductile iron casing/carrier pipe installations (I think as referred to by cvg) is mentioned in ANSI/AWWA C600 Installation of Ductile-Iron Water Mains and their Appurtenances as well as AWWA Manual M41. In the international field, a good bit of concrete-sheathed ductile iron pipe has even been used particularly in Japan and the Middle East for uncased jacked/trenchless crossings of substantial carriageways, and such makes for a quite formidable composite pipe.

 

[JohnWeal]

Many thank cv god and rconner.
This pipe will be installed in Kurdistan region and not the more common oil field type sand areas.
I am puzzled why the drawings show PE100 pipe just for the road crossings hence my post!!
Especially as in some of the cases we are up to 17 bar and that's without surge possibilities.

Regards
John

 

[LittleInch]

I was thinking you didn't mention location or whether the crossing was of new roads, open cut, trenchless or such details.

PE100 SDR 11 is good for 16 bar as I'm sure you know which seems high for push fit spigot joints to me.

I can only guess in Kurdistan in the past that the road has sunk and pulled the pipe with it or earthquakes have also resulted in sprung pipe where the road has been a more solid item than the pipe. Also open ct road crossings tend to suffer from collapse, compression and shock loading as the trench is never put back right so PE is a much more forgiving material than DI.

In the main though if you're auguring or other trenchless types of crossing I would have thought you need a casing of some sort but that size of pipe is huge to go under a road - what are transporting? the entire water supply of Kurdistan? - it's not that big a place

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[cvg]

pressure rating is not a factor.
ductile iron with push on joints can be designed for 350 psi working pressure (plus 100 psi surge) for a total of 450, see Table 7 in ANSI/AWWA C151/A21.51 “Ductile-Iron Pipe, Centrifugally Cast, for Water” Higher pressure design is also available. Push on joints allow a significant amount of flexibility, so some settlement can be tolerated. However, for a pipe this size and cost, I would make sure the "trench gets put back right"

https://www.dipra.org/ductile-iron-pipe-resources/frequently-asked-questions/design

 

[JohnWeal]

LittleInch,

We are pumping 630 MLD in two parallel pipelines each 1600mm diameter.

In the U.K. We use Saint Gobain 'natural' for drinking water supply pipelines. It has from 4mm to 9mm cement mortar lining depending on diameter.

Difficult to understand why the material change under the road unless the chief engineer is perhaps worried about making the spigot joints over approx 40m.

Does this have to be an open-cut installation?

It is normal for the top of the casing pipe to be 1.7m (5.5 ft)from the road/rail. So that's a deep trench.

But as I'm not an installer I don't know if 1.7m plus trench depth under pipe is considered 'deep' or it's common installation detail for pipe crews.

Grateful for your help and have a great weekend.

Regards
John

 

[cvg]

minimum cover is generally at least two feet (600mm) in order to reduce the dynamic loading from traffic. More if it is below a rail line.

your trench is 1700 plus 1600 = 3300 total to the bottom. that sounds reasonable within a highway right of way. The government or other right of way owner should be dictating whether it goes in a casing or if it needs to be jacked and bored, or not.

 

[rconner]

In the USA I believe large diameter crossings of major highways, i.e. with high traffic volume no one really wants to divert, are often accomplished by a trenchless process often referred to as "jack and bore". The steel casing pipe is first jacked into place, followed by the carrier line with same often assembled and installed with the same shored jacking pit and even with the same equipment to jack the casing into place. When installed in this trenchless manner, the design invert is typically much deeper than what cvg mentioned (I suspect he was likely referring to open cut of most common smaller pipelines) primarily to reduce any chance of disturbing the roadbed and paving/traffic support by the trenchless excavation etc.