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# Jack-and-bore under-roadway crossing for 6"-10" pipe

## Jack-and-bore under-roadway crossing for 6"-10" pipe

(OP)
To install 8" water main under-crossing a roadway. If open-trenching is not allowed, is jack-and-bore the best/low-cost method to use?  Versus, directional drilling? Are there any known problem areas to this approach? Any good references concerning this method?

### RE: Jack-and-bore under-roadway crossing for 6"-10" pipe

Boring-drilling and jacking is a good method to use and is routinely done.  Problem is depth of excavation needed to get the boring-jacking machine down low enough to push the  pipe in below the minimum cover required for the pipe under the road.  Soil suitable for boring and jacking is required.  Rock would require tunneling.

Horizontal drilling is more dependent on pipe and soil conditions.  Disadvantage when compared to horizontal boring is the stand-off distance needed to slowly curve the pipe down under the road, cross underneath, and curve it up on the other side, without overstressing the pipe in bending a radius too tight.  I'm guessing you will need a radius of around 1000 feet, although I don't know the wall thickness of your pipe.  Say 800 to 1400 ft radius might be average.  So using that radius, you have to curve down, curve flat, then curve back up then curve horizontal again.  You may have to get back away from the road several hundred feet to begin the drilling poing, use a heavier wall thickness pipe, and receive the pipe several hundred feet on the other side of the road.  Large bolders that can deflect the boring head are a problem as well as sand that can collapse around the bored hole before the pipe is pulled through.

Going the Big Inch!
http://virtualpipeline.spaces.msn.com

### RE: Jack-and-bore under-roadway crossing for 6"-10" pipe

We have had some recent cave-ins in Michigan where the jack-and-bore contractor got ahead of themselves.  Caused the shutdown of a major highway off-ramp in one case.  Two of the cave-ins involves dry, poorly-graded sand soils.

Another thing to be aware of with both techniques is bolders.  They can cause problems.

### RE: Jack-and-bore under-roadway crossing for 6"-10" pipe

Gray and ductile cast iron pipes have been e.g. push inserted inside various types of casings e.g. installed by various boring, jacking, and tunneling means as well as larger existing pipelines for many decades.  This has been described to some extent for many years with regard to "Highway and Railroad Crossings" in a section of ANSI/AWWA C600 as well as AWWA Manual M41.  I agree with Mr. BigInch that boring, jacking, or tunneling with conventional casing pipe, and then placement of a carrier pipe (often from the common boring/jacking etc. pit) for watermain or sewer service, is probably still the most common approach.
There are however now available many styles of quite formidable strength ductile iron pipes that can also be installed by many different “trenchless” (or perhaps more accurately in many cases, “less trench”) means, e.g. as can be observed through the portal   http://www.acipco.com/adip/trenchless/) where same procedures are preferred and acceptable to authorities.
We have seen increasing numbers of these projects since the early 1990’s, with a marked increase in horizontal drilling projects with flexible, restrained joint ductile iron pipe since 1996.  I would only further point out that with contemporary ductile iron joints/systems, the long piping assembly/layout area mentioned in some of this thread (as a disadvantage common to HDD with other types of pipes) is not necessary with ductile iron pipes, as the very rapid assembly of these contemporary joint structures does not require lengthy field welding and/or cooling periods, and thus also allows for quick insertion of individual pipes, e.g. in a relatively short “pipe insertion/assembly pit”, in “cartridge” loading fashion.  In fact, in the first 6” (`150 mm) ductile iron project I saw installed by HDD in 1996, I think the pipe never even hit the ground after a pulling head was assembled onto the first plain end and dropped down to connect to the drill string behind the reamer, but thereafter the pipes were basically loaded from a stack on a flat bed truck that was parked next to the pipe insertion pit, which in turn was basically just a “trench box” for worker joint assembly safety that had been quickly dug/sunk into a rectangular trench with a backhoe that the contractor had drilled to/reamed from at desired pipe depth.

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