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
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.
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RE: Jack-and-bore under-roadway crossing for 6"-10" pipe
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
On a recent project, 6" diameter pipe was directionally drilled instead of jack and bore. When you get into the smaller diameters it is not economical to put the pipe in a casing. The casing pipe should be 6" larger on all sides or plus 12"
RE: Jack-and-bore under-roadway crossing for 6"-10" pipe
Here's how to design a HDD,
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RE: Jack-and-bore under-roadway crossing for 6"-10" pipe
For directional drilling in most soil conditions bentonite or polymer is needed. This should hold the excavation open preventing the collapse of soil, including sand, before the pipe is pulled through.
I think directional drilling would be the more economical method for a 6-10" water main.
RE: Jack-and-bore under-roadway crossing for 6"-10" pipe
Most of the municipalities where I work require casing for water and sewer work.
RE: Jack-and-bore under-roadway crossing for 6"-10" pipe
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RE: Jack-and-bore under-roadway crossing for 6"-10" pipe
RE: Jack-and-bore under-roadway crossing for 6"-10" pipe
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.