General Questions about Horizontal Boring for Utilities

[cieg22]

Hello, all.
I've never worked with horizontal boring before, and I could use some pointers.

I'm working on a conceptual design for a new building. There are no water/sanitary mains in the street in front of our site. There are mains in a nearby intersecting street, that we plan to connect to. Sewer would need to be pumped. The Township also wants us to extend the water main, rather than tapping in with a connection. Code requires cast iron for both. For conceptual purposes, I assume we'll be putting in a 6" water main and a 2" forced sewer lateral. The connection point is about 120' from our site (paved the whole way).

I have some general questions about the boring process:

Is it feasible to install cast iron? If so, how do you ensure that the pipe has proper bedding?

I expect that our ground water is very high. Is dewatering any more than a headache than with open-trench? Are there any othe concerns?

Does anyone have a rough idea of costs for this process? I've been quoted $35/ft for the 6" line and $20/lf for the 2". However, I get the impression that this is a price for installing HDPE pipe, which I assume would be much easier.

Are there any other issues you'd recommend taking into consideration?

Thanks in advance, everyone, for your time and help.

 

[bimr]

Directional drilling with "ductile iron" pipe is feasible and can be done without much trouble. Bedding is not an issue since installation wiill be with a directional drill method.

Dewatering should be less of an issue than with open cut installation.

You should plan on having an inadvertent frac-out and/or mounding. You also need to allow space for the staging areas. You should plan on doing underground investigation and locating using potholing. You also have to allow for the turning radius of the pipe.

A more reasonable cost estimate is $75/ft for the 6-Inch and $65 for the 3-Inch ductile iron.

Note that water main is typically a minimaum of 8-Inch and sewage force maine are a minimum of 3 to 4-Inch

 

[coloeng]

Other things you need to consider are the soil conditions. Because the bells on DI pipe are have a greater diameter than the body of the pipe they may tend to pull the soil and create more resistance to the pull back. I have seen pipes get jammed and broken when pulling them back. This can especially occur in very sandy or cobbly soils. HDPE or fusible PVC can help alleviate this problem.

Unless there are other factors that make open cut more expensive, open cut is usually more cost effective, even under paved areas.

 

[rconner]

Ductile iron pipe, and gray cast iron pipe before that, has been installed with great success and essentially also to line and grade in “trenchless applications” such as jack and bore, casing and carrier pipe as well as “sliplining” (of other failing pipe material) applications for many decades. For the last few decades, various ductile iron pipe/joint configurations have also been successfully pushed and pulled directly into the ground worldwide, without casing pipes.

While I am aware of many problems with HDD installations of welded steel and fused plastic pipes (e.g. getting collapsed, drawn out and/or being hung up etc. or locked into position before successful placement for various reasons etc.), some ductile iron pipe manufacturers have on the other hand had minimal problems, as they have furnished specific flexible restrained joining systems for at least 14 years that have not proven to be significantly obtrusive in pulling loads, nor inherently breakable as was indicated in a prior post.

The joining systems of such strong and flexibly joined ductile iron pipe HDD installations can be pulled essentially as “chains” in a borepath (normally made fluid and stabilized with drilling fluid and soil cuttings), and without having to bend or bind the curved pipe barrel against the borepath wall as is necessary with welded or fused pipelines (the latter with also obviously putting incumbent bending stress in the pipe wall to deal with in any curved section, in addition to all other installation and eventually service loadings). One explanation for often very low pulling loads of many common sizes of ductile iron pipe for HDD is that the weight of empty pipe more substantially off-sets the “buoyancy” of the pipe in a fluid borepath. Once the line is placed, there is incidentally no problem now or in the future tapping that piping installed in curved alignment (e.g. for air release or services etc.), as has reportedly occurred with bent or axially loaded plastic pipes.

[Incidentally, while not saying it does not have utility, it is my understanding also fusible pvc has a service history in the USA of only ~ 6 years.]

 

[JedClampett]

Take a look at this:

http://www.dipra.org/pdf/HDD-brochure.pdf

It's a great publication.

 

[csd72]

I have some experience with HDD but I have never used it for ductile iron so this is an eye opener for me. It seems rather behind the times that they are specifying DI as over here in the uk they are all being replaced with PE or concrete pipes due to their greater ductility and durability.

A few useful sites:

http://www.eco-drill.com/auger.html

http://www.astt.com.au/trenchguide.htm

http://www.nastt.org/store/technical_papersPDF/

 

[cieg22]

Thank you all so much for these responses! This is more info than I could have hoped for.

One last question - I noticed that a number of you mention DI pipe. Would the same comments apply to Cast Iron? Unfortunately, CI is the only acceptable material listed in the Township Code, and I already anticipate a long review process......

Thanks!

 

[bimr]

Cast iron was replaced by ductile iron some time ago. It would be considered equivalent.