Ductile Iron Pipe Protected by an RC Pipe Sleeve

[Kinemenematics]

Bought about a whole lot of 3m long 450mm reinforced concrete pipes to be used as protection for my ductile iron pipes, which will be running up to a 100m under a main road.

Ran into two problems (and I still want to utilise those pipes):
1. If I place my two DI pipes, or even just one DI pipe, into these RC sleeves (diagram attached), and suppose I just clamp them, will my DI pipes vibrate excessively during a hydrostatic test, up to the point that the DI pipes would somehow disengage from their spigot/socket joints?

2. What about an adequate replacement for thrust blocks since i can't place thrust blocks inside these RC pipes.

Thanks!

 

[Kinemenematics]

woops the attachment is here

 

[robyengIT]

pay attention to the design of RC pipe too and its laying conditions

 

[LittleInch]

I'm struggling to see why you've done this, but leaving that aside, push fit pipes in a straight line, so long as you have enough clamps (how are these being fixed? how far apart?) should be ok until you come to a bend or tee, then just anchor it there.

what is the construction sequence here - concrete pipe first, or with sections of pipe pre installed?

All very odd.

I don't understand where you are getting the vibration from - especially during a hydrotest there should be no vibration for anything.

Why DI? for this section can't you use PE or steel and then just insert it or drag it in.

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

 

[bimr]

Your pipe will not vibrate from the hydrostatic test.

You will have to use restrained fittings, not bell and spigot. You should use spacers inside of the concrete pipe as well.

http://www.ebaa.com/files/pdf/brochures/Brochure.1100.pdf

 

[bimr]

I just looked at your sketch.

You do not want the pipes laying on the concrete as it will cause corrosion. You also do not want to clamp the pipes like you have them shown. You should have only one fixed constraint and allow the pipe to move with the temperature changes. You probably will have to have custom spacers made up.

http://www.apsonline.com/casingspacersendseals

 

[rconner]

Ductile iron piping and gray cast iron piping before it have together been installed successfully for a century or more inside casings and tunnels etc. of all materials, as well as being installed uncased, under roadways. Traditionally, these pipes when cased have most often been assembled in cartridge fashion from adjacent​ access pits, and then pushed inside casings under "main" roads with the same equipment used to jack and bore the casings. However, in the last few decades ductile iron piping with restrained joints has also been successfully pulled in place. The only supplied sketch of this one in the OP (as others have noted) nevertheless begs some questions. To help in this process, might start with the following:

1. How is the concrete casing to be installed under the roadway (by open cut, or instead by trenchless means, e.g. jack and bore etc.)? If the latter, that may perhaps be more common at least for existing "main" roadways, how is it planned to dependably form/pour? the inside level flat apron the full length on which the pipes are apparently to sit and at some point to somehow apply the clamps/bolted tie downs (450mm/~18" inside diameter casing occluded by a few inch thick apron as well as the carrier pipes would at least be a rather "tight fit" for the bolter!!)

2. While it might be possible at least with an open cut installation and special "exact length" pipes to do something functional that looks like this, do you also really want (as it appears two pipelines) permanently tied/bolted down up inside a long casing up under a roadway? It would appear that may be doing away with some of the published Engineering advantages of casings to begin with (e.g. the ability to readily upsize or replace a damaged line at some point in the future, if that were ever wanted?)

3. I suspect it is for similar reasons, and that you apparently may also have the casing pipe available, that bimr has suggested "custom spacers" (I think there are folks who will, furnish slick spacers that will position individual or for a price multiple lines in one casing, and also restrict same from unduly floating or moving around, as I believe is are incidentally other intents of installation requirements of pipes in casings e.g. ANSI/AWWA C600 standard).

4. Didn't see whatever "thrust blocks" you may be referring to in your sketch, but agree with bimr you can often substitute appropriate utilization of restrained joint ductile iron piping (thereby eliminating that need).

 

[Kinemenematics]

NEW QUESTION:
Suppose I bury these concrete pipes with just 3ft of cover. Would these RC pipes fail? They've got work-proof strength of 45kN/m and crushing strength of 52kN/m. Soil is clay-silt.Link Could you help me check if my calculation is flawed? (File Attached)

LittleInch:
They will be laid inside an open trench. Concrete pipe first and then D.I pipes slipped in. I suppose D.I. cause of contractual limitations. And the pipes have been bought.

BIMR:
It's a spigot and socket joint D.I. pipe. Also, how will laying the pipes on the concrete cause corrosion? I'm thinking of injecting a sand-water mix once the pipes have been clamped and laid. OK I get the spacers thing and avoiding clamps; sadly spacers aren't ready available in my country.

As I understand there is ~5degrees of deflection allowed at the D.I spigot-socket joints. I suppose then that injecting the annulus with sand-water is the other option I have..

RCONNER:
1. Open cut. Yeah, it would be a real hassle, so I'm thinking the strap/skid restraints will be about 3m apart.
2. I'm having fingers crossed for 40 years of maintenance free operation...
3. One other problem with the casing pipe bought is that by calculation, I need to bury these pipes with 1.5m cover.
4. Good idea.

Thank you!

 

[bimr]

Mixtures of soils in backfill may cause corrosion. In the ground there are usually areas of varying nature which might form galvanic cells. Clods of clay, for example, mixed into a sand backfill will lead to sever corrosion where the clay contacts the pipe. The same phenomenon causes corrosion on pipe exposed to soil and concrete or other highly alkaline backfill. The problem often develops where a pipe passes through a concrete wall or floor. The resultant cells lead to corrosion of the portion of pipe exposed to the soil.

The spacers are used to align the pipe within casing, and have nothing to do with the pipe joints. The pipe joints should be restrained in some manner unless the pipes are buried. Pipe clamps are not suitable for buried applications.

Why don't you just bury the pipes without casing?

 

[rconner]

Not to attempt to engineer or re-engineer what you've got here and trying to stay within the basic pipe/casing constraints you laid out (but still trying to accomplish the intent of minimum standards as much as possible), I would just want to throw a couple concepts out for discussion. I wonder if it would be possible for someone good with the tools/hands to basically craft (and maybe rather quickly and reproduceably/economically, ​with say a template and a bandsaw) some otherwise simple shaped skids to simply and firmly band periodically to the pipes as they are pushed in? I guess what I am talking about is taking some say ~100x150mm (4x6 inch) rectangular timber or plastic stock and basically cutting it in workmanlike manner to a shape something like what is depicted in the attached crude sketch. If they couldn't easily cut the small pipe radii/saddle, maybe could simulate same with essentially a V-notch. [I guess it wouldn't hurt to notch these skids circumferentially as well near the axial center the width of the banding, so same can't come off]. If the banded together pipes are to be pushed any significant distance up the casing, it may also even be necessary ahead of time to anchor some guide angles/channels to the inside of the concrete pipe above the skid ends so that the unbalanced twin lines can't twirl around (like licorice!) as they are pushed in, and also flare the ends of the guide channels up so the skids don't get hung up on same as they clear the concrete joints! I guess also wouldn't hurt to lubricate the bottom of skids or casing when they are installed with say something like pipe lube that wouldn't hurt the pipe or system to minimize force required.
While I am also not an expert in the process, as I have not seen same done myself, I believe one traditional means of stabilizing pipes/joints (per your OP question?, and to some extent even environments?) at their installed position within some casings has been with the use of (air) "blown" sand. You can see one reference to same in e.g. ​the specifications at

http://mnwd.com/wp-content/uploads/2013/05/02315-Jacked-Casing.pdf

. Once the sand settles around the pipes, it would appear you would basically have two pipelines embedded roughly where they are supposed to be in sand (and fully so between the skids), with the skids or spacers perhaps not doing much or needing to do much from that point forward?
Perhaps an advantage of clean sand as opposed to grout is also that if anyone ever wanted to in the future it might be washed/drained out of the casing, if that were ever desired for any reason?

 

[rconner]

[p.s., a good place for skids, or for that matter any sort of supports for ductile iron piping systems, is say within a couple feet behind the bells as depicted e.g. at pg 7-19 at

http://www.american-usa.com/system/...e_Iron_Pipe_and_Fittings_Manual_(3-16-15).pdf

]

 

[LittleInch]

To be honest I think this whole design is a complete dogs breakfast. The design is nigh on impossible to construct and offers no advantage over simply laying the DI pipes in the ground secured with concrete anchors and guides to prevent axial movement of the pipe.

you might already have bought these items, but it doesn't mean you need to use them here or that the design is a good one - it isn't.

DI and reinforced concrete pipes buried at this sort of depth are not at risk from collapse due to weight or traffic loads, only from settlement.

I honestly think you need to rethink this design as it will take much longer to build and will not look anything like your nice drawing.

sorry to be critical but I can only judge on what I have seen and so far it doesn't look good I'm afraid.

Casings are fine, but only really of use when you can pre-install and then insert your main pipe or pipes. This size is not big enough for man access, but too big really for the size of pipes. Casings can become transits and can fill with water, animals etc, but filling them in reliably is very difficult and costly.

compared to the alternatives available it doesn't seem to make sense to me.

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

 

[bimr]

Kinemenematics, is there a reason that you have proposed the casing? Several posters are advising that there is no need for the casing.

In addition, if the pipe requires replacement in the future, you can replace it without digging up the road using HDD, or boring.

 

[Kinemenematics]

The issue I've faced is really more of a commercial fault of a contractor - they bought pipes based off the wrong BQ - My company is just trying to maintain relations with them. However now that all the comments are quite unanimous here that the casings are more trouble than they're ever worth.....

rconner, looks like an interesting solution, and I've seen a similar concept where the skid is precast with the casing. Thanks for the idea- although timber skids look costly. Are you suggesting this be the only support or M/Js or spacers too?

Littleinch - It is. Because it does take much longer to build. Lets say I use restraint harnesses for the pipes, and then fill up those casings with sand/water, AND use timber piles (pg 7-19 at

http://www.american-usa.com/system/assets/346/orig...

]) Even if it's dogs breakfast, would it be plausible?


Anyway, to add onto the scenario, the pipes will be below unsurfaced roads for 2 years before the entire construction area will be filled up with another 800mm of soil.

 

[LittleInch]

Ok,

I'm not sure of your experience so apologies if this gets a bit basic, but then it covers everything.

page 7-19 is for above ground piping.

You normally only use a pipe sleeve like this if you either:
need to install this before your main pipes are ready
You need to add things in the future (pipes, cables etc)
You need to protect the things from excessive forces

In your instance I don't believe you need to protect new DI pipes from any forces imposed by a road 3 feet or more above it.

I would simply lay the DI pipes in the trench, possibly surround them in lean mix, or well compact the soil around them in a straight line and level and then anchor at the point where they change direction or enter your pit. If you are really nervous about them being damaged by the road above, lay some precast slabs over them. Use the concrete pipes for something else or sell them.

The difficulty with your current design is how you lay the base layer in whilst getting access to the pipes to bolt them down. I can't see a construction sequence that would work. Also the cross section seems to ignore the fact that DI push fit pipes have a flared female end with a larger OD than the pipe, hence they would be spanning from one end to the other.

I've seen this and tried many times to work around an original error, when in the long run the best thing by far is simply to admit the error, take the pain and get the right thing. What was on the original BQ?

If you really really want to use these concrete pipes then I would lay the concrete pipesto your line and level, insert your DI larger pipe in from the open endpushing one joint at a time, with the larger flared end protected by some plastic nylon, PTFE, PE something like that. Then flood the pipe up to halfway with a sand cement mix, let it of off and repeat for the second pipe. A complete waste of time and money, but as far as I can see that's the best way out.

Let us know how it goes - some pictures are always good!

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

 

[ZDR1985]

I believe the reason for the pipe sleeve is Non Destructive Road crossing (NDRC).

You can make your DI pipes restrained by using restrained joints on socket end, and weld bead on the spigot end to accommodate the restrained joints.

 

[rconner]

In the USA I'm guessing 4"x6"x8 feet long rough-cut oak timbers might run somewhere in the neighborhood of 16-22 USD each. If the cost of such timbers were say 24 USD per each and one were able to cut six of the skids/spacers I rough sketched from each, that would put the material cost per skid/spacer at say no more than 4 USD each. With say two skids per each 20 feet (6 m) pipe, this would put the material cost at 8 USD/20 feet or 40 cents/foot (or roughly 1.3 USD/meter) of crossing​. One would of course then have to add the labor and equipment for (saw?) shaping the skids/spacers, as well as banding and any stabilizing angles/runners etc. I guess these skids would be more or less "permanent" supports within the casing, or at least until the sand is blown in to surround the pipes in the intended positions within the casings. Assuming you have competent soil strata below where the casings are to be installed however, I doubt you need any other special supports e.g. exterior piers or piles.
As to intended purpose(s) of any sorts of "casings" used with any sorts of piping materials, I know ASCE MOP #89, "Pipeline Crossings" (1996) discusses varying philosophies of cased and uncased crossings with nearly a half century of background, and after recommendations to consult local, governing authorities it lists the "advantages" of casings as basically mechanical protection, ability of future removal or replacement, frost line insulation, sub-base and crossing protection in the event of a carrier pipe leak, and protection from third-party damage. As others are at least hinting in replies thus far, it also mentioned trends are toward more uncased crossings, perhaps influenced by the disadvantages also listed there of higher cost (and larger borehole, when all installed trenchless), two pipe installations required as opposed to one, extra cost of insulators or spacers as well as end seals, installation of casing vents, and when specified annular space "grouting" of carriers inside effectively does away with some of the "advantages"!
While not involved in this inquiry, I would only add casings (or sleeves) have also been employed in recent years also for some distance down in the entry area (and throughout) of some substantial horizontal directional drilling installations, I believe to somewhat stabilize areas that might otherwise become quite mucky and unpredictable due to the motions of water and drilling mud/cuttings etc.