Directional Drilling sewer pipe 2

[looksatstars]

I was wondering if anyone had any experience with directional drilling sewer pipe.
I'm very interested in doing a small project (150metres) this way. I heard you can use a conintuous length of PE pipe and fuse the connections as you go to keep adding length.
I would like to hear any opinions if anyone has done this kind of placement.
Thanks

 

[TDAA]

I was involved on the construction end of this set up once. The design engineer was likely to not do it again.

We had a very steep cross slope, adjacent to a busy highway, which they did not want to alter much to allow equipment access. This lead to the DD. Unfortunately, the pipe was designed near minimum slope, and we ended up with some reverse flow near the end due to the drilling technique. A section of pipe at the end had to be removed, and a manhole was shifted to be avoid any connection type issues.

I would say it is feasible, as long as your design allows for some change in slope, and that your slope is definately above minimum.

 

[jartgo]

I've never done it with gravity pipe, but it's commonly done with force mains. The pipe would generally be fused in one long length, then pulled through the previously bored hole. I've had no problems, but again, I've only used it in a force main situation.

 

[looksatstars]

Thanks TDAA

In talks with some collegues, I found out the same thing. The HDPE pipe comes in rolls so it is very hard to lay it flat even when directional drilling. So it is, like you say, only should be used in high slope areas.

Its amazing, when directional drilling is cheaper than conventional. Good to see technical advances such as these.

 

[rconner]

HDD is typically accomplished with drilling fluids and/or at depths that invite the presence of groundwater around th epipeline. I understand drilling fluids and/or mixes of drilling fluids and soil cuttings are typically a more dense "fluid" than even clean water. While often touted as a selling pitch, in reality "lightweight" hdpe pipelines, even e.g. if somehow/presumeably weighted full of water, have a bulk density less than (and will float in) even clean water, let alone any heavier fluid like fluidized soil!) While I am aware there have been some folks who claim they can HDD (and even promoting hdpe for this installation) to grade, e.g. by not over-cutting much, in reality it has been perhaps been kind of hard to fool ol' Archimedes (Archimedes Principle) for a couple thopusand years/everywhere in such a disturbed environment. Other types of piping materials are available for many trenchless installation procedures, including HDD.

 

[ufcivilengineer]

I've designed a directional drilled gravity pipe. The gravity pipe itself is typically inside a casing. The casing allows the gravity pipe to have a continuous and constant slope.

 

[jartgo]

Doesn't that mean you've directionally drilled the casing, not the carrier pipe?

 

[Zambo]

I would be very surprised to hear that it is possible to directionally drill a gravity sewer pipe. Generally the accuracy of directional drilling is suitable for pressure pipes.

I didn't really get rconner's point, but HDPE is suitable for use in directional driling for pressure pipe - water mains for example. The drilling fluid would normally be bentonite or polymer.

Fot trenchless installation of sewers the required accuracy can be achieved with pipe jacking or micro-tunneling. In this case due to the heavy duty pipes needed open cut is usually less expensive if possible.

 

[dicksewerrat]

The technology is available for HDD to install gravity lines. It is the contractor that you have to investigate thoroughly. This process can install a line that is just as accurate on line and grade as an open cut line. HDPE is fine for graity and pressure mains.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[TBCEng07]

I agree with dicksewerrat. It depends largely on the contractor's ability. HDD Sewers can be done, but the contractor has to work more carefully and often slower to be sure he doesn't deviate from the proposed grade. You also are going to want to be sure of the type of soil you are boring through. if significant boulders or differential soil conditions are found, it can push the bore head off of the desired alignment and grade.

 

[rconner]

Hummm… I will try to be a little clearer. It is my understanding sags are areas of a sewer line that (e.g. in a video inspection, after water has been introduced into the line) have the appearance (i.e. from depth of ponded water) that an area of pipe has settled. I believe ponding can be due to the line simply being installed by the contractor to the undulated grade, subsequent settlement of the area after installation (as is probably/frequently assumed) , or arguably less obvious relative flotation of the pipe in wet or otherwise liquefied soils on each side adjacent the apparent “sag”.
At some degree of severity, I believe some sag “defects” have been implicated in eventual sedimentation/formation of slimes, accompanying generation of hydrogen sulfide, various blockages, and maybe even some subsequent overflows with potentially now quite serious contemporary ramifications (at least in some areas). As a consequence, I also believe that for whatever reasons at least some jurisdictions/authorities are attempting to enforce quite stringent sag inspection criteria, at least for new construction and even on gravity sewers laid to slight/quite flat grades, e.g. in some cases ostensibly allowing no more than ½”-5/8” of standing water.
I suspect those (at least those carefully studying the issue) who advocate installation of plastic (very lightweight, slick on at least the outside) gravity pipes by HDD, or maybe even by other means in deep wet, high-ground water areas are doing so by suggesting relaxation of the sag criteria, a substantial increase of design sewer grade, or both. While I am not knowledgeable enough to gauge the long term effects (if any) of the former practice, I know the effect of the latter increase of the design grade can be that one gets quite deep in the ground quite fast on the way to the plant (I believe not generally helpful when trying to serve a large area with gravity pipes!)
I have incidentally been a proponent of trenchless construction, as another tool in the toolbox, for about 25 years. I have therefore watched the rapidly developing “technology” as closely as I could. While I have great respect for the ingenuity/value of some “contractors” and developments of “technology”, I have even more respect for the laws of physics/geo-physics and I believe some caution is in order lest over-selling without detailed education set the industry back some in this area.

 

[CharlieConklin]

Regarding directional drilling of gravity sanitary sewer pipes, it is possible with conventional HDD at slopes steeper than one or two percent, but if you want to have a controlled or lesser slope, you need to use the ArrowBore (TM) process. It is a patented process that improves the HDD method by controlling the slope and depth of the cutting head and drill rods. I liken it to what microtunnelling does compared to regular bore & jacking. You can use HDPE, but it helps to use a stiffer pipe like C900 PVC pipe (CertaLok). The City of Orlando and Orange County Florida have used the method and it works pretty well under most conditions. You won't get perfect results where you have hard rocks that might deflect the cutting head, or loose sand below the water table when attempting an extremely low slope, but it is a very effective method under most normal conditions. If you want further information about the process, you can contact:
Ted Dimitroff - President
Trenchless Flowline, Inc.
7850 East Highway AB
Columbia, Missouri 65201
573-449-6186 - office
573-449-1031 - fax
573-268-2294 - cell
tdimitroff@trenchlessflowline.com

 

[YoBob]

I have used directional drilling for gravity sanitary sewer pipes.
First, it is important to understand the distinction between directional boring and underground boring.

Gravity sanitary sewers cannot tolerate 'porpoising' or humps in the pipe. With conventional horizontal drilling, a strait, concentric bore cannot be assured due to rocks, lack of precise control, ect. This is why open trenching is the method of choice. However, in the case of highway or stream crossings, a trench may not be tolerated. Enter directional boring.

For example, say we wish to route a gravity sewer pipe under a highway. With a directional bore, two large pits are dug on either side of the highway. Next, a steel pipe sleeve is driven between two target inverts. The soil on the inside diamter is extruded in this process. The PVC sewer main is placed inside this sleeve. The PVC pipe is maintained concentric inside the sleeve using special hardware.

Directional boring is expensive due to high mobilization cost, tight concentricty tolerances and expensive special equipment. I completed a 50 ft section for $30,000.00. Most of this was for mobilization.


Hope this helps.

 

[Zambo]

YoBob,

by "directional boring" are you referring to microtunneling or pipejacking?