Strongest Culvert material 1

[nutbutter]

I'm looking for the best culvert material to use in a specific application. The culvert will be running under a haul road that is basically a 2' thick aggregate road. The top of the culvert will only be covered by 18" to 24" of aggregate roadway surface at it's point of minimum cover. What would be the strongest material to use in this circumstance? I'm thinking CSP would be good? We usually use HDPE, but I don't think it would be good in this instance.

Take care,
Stoddardvilla

 

[eric1037]

We have used a steel outer casing (not corrugated) for pipes like this in the past.

 

[civilperson]

Class V Reinforced Concrete Pipe is the strongest pipe for the application cited. Using 100 psi flowable fill for backfill will enhance the available strength.

 

[VAD]

Steel casing is fine. Depending on what vehicles are using the road, the CSP would be fine as well. Generally 12 inch min can be used. HDPE as well. However, if cost is not an issue and you do not want to worry about aggregate cover reduction on a haul road that will inevitably occur then choose steel. Your call

 

[SlideRuleEra]

Concur with civilperson. Concrete pipe has the advantage of not only having high strength, but also a significant wall thickness (compared to the diameter). This means that the geometric properties of the pipe itself (moment of inertia, section modulus, etc.) are formidable.

http://www.SlideRuleEra.net

 

[rconner]

Ductile iron pipe, e.g. per ASTM A716, Standard Specification for Culvert Pipe with a minimum yield strength of 42,000 psi and a Young's modulus of 24,000,000 psi, is a quite formidable culvert pipe. It is available in minimum tabulated thickness included in that standard, as well as several heavier thickness classifications in other standards referenced therein. When available cement mortar lined as opposed to bare or asphaltic-lined pipes are utilized for this purpose, external loading design should be checked for such pipes per ANSI/AWWA C150/A21.50 and/or DIPRA's "Truck Loads on Pipe buried at Shallow Depths" when applicable etc.

 

[nutbutter]

Thanks, everyone for the valuable posts. I'm thinking about using class V RCP just so I don't have to worry about it. Like I said, it's only going to have 18" cover of aggregate (which is also the road surface).

Does anyone have a good reference for comparing the costs of these different pipe materials? I know HDPE is the cheapest, but how do RCP, CSP, and ductile iron compare? I'm sure ductile iron is more, but I have no idea how much more.

I used to have a sheet for estimating that called out a price per foot for different pipe materials. Unfortunately, I can't find that sheet.

Take care,
Stoddardvilla

 

[civilperson]

Call your local concrete pipe manufacturer for material costs. Comes in lengths of 6' to 7' depending on diameter. use $20-30/ft installation cost for budget purposes for a contractor already mobilized with excavator on site.

 

[nutbutter]

I guess I was wrong, and it looks like the culvert will only have 12" of aggregate cover or so. The road is a 24" aggregate haul road, so in effect, this culvert will be right in the middle of the "pavement" structure. It runs perpendicular to the road.

I'm trying to do the calcs right now with RCP (class V). I was considering the flowable fill as mentioned above too. How exactly does one use that? I don't know how the flowable fill would fit into my calcs though, so I may just go for it without the flowable fill. I'm almost tempted to just use DIP, save some time, and call it good.

Finally, what is the strongest culvert material available? Is it DIP? I would assume strength is probably in this order (strongest to weakest):

DIP
RCP
CSP or CMP (however you call it out)
HDPE or CHDPE
VCP

Can someone correct me if I'm wrong?

Peace,
Stoddardvilla

 

[SlideRuleEra]

The strength of the "material" is only part of the solution - the strength of the "pipe" is what is important.

Concrete pipe is a rigid pipe system that is over 85% dependent on the pipe strength and only 15% dependent on the strength derived from the soil envelope.

http://www.concrete-pipe.org/why.htm?cp_Session=40a348f898b1807f1d0311b8c660580f

IMHO, from what you descibe, this in NOT an occasion where precise engineering calcs will provide an answer - there are too many unknowns. Just use the best materials for the conditions and don't worry about it.

http://www.SlideRuleEra.net

 

[eric1037]

How about using a smooth steel casing pipe? With only 12 inches of aggregate, that would be my recommendation.

The advantage of the casing is that it will allow for some movement at the ends. That way your pipe won't deflect due to loading.

 

[cvg]

a better option would be to raise the profile of the road slightly as you go over the culvert providing the necessary cover over the pipe.

 

[rconner]

SlideRuleEra,
I noticed the quote you provided, it appears from ACPA. How about their statement also relating to their concrete pipe verbatim from their more recent ad in October 2006 Civil Engineering magazine, "Its inherent strength means it does not rely on soil support to provide the necessary structure, because it is the structure."
While I think I know basically where they are coming from and agree that all responsible engineers should carefully scrutinize the performance of particularly long-term weak, creeping types of piping (e.g. to make sure they are suitable for the level of soil support that can be practically expected in their application/area, and they will function for the Owner) that I suspect at times deal concrete some fits in the marketplace with attractive prices, "IMHO"(for whatever that's worth!) the latest ACPA ad statement is however arguably some "over the top", and perhaps even foolhardy.
While these are no doubt quite catchy words and may even sell some pipes, in my humble opinion particularly if/when you don't get good uniform support along under the haunches of any pipeline, greater loads than commonly anticipated can come to bear on some buried piping, concrete or otherwise, where it does happen to be supported by the soil mass, and these greater loads (perhaps not obvious to all practitioners in a promoted basically only two-dimensional design) might/do in some cases? compromise the load factors or longitudinal bending strengths/abilities/ductility of concrete pipes.
Thus contrary to the current claims of ACPA, I believe ALL PIPELINES REQUIRE SOME "SOIL" or other external "SUPPORT" to function properly!

 

[VAD]

rconner:

I generally agree with your comments especially the requirement for good uniform support from bedding and at pipe haunches. This is where sand or sized granular material plays an important role. However, for a CSP for example the performance is highly dependendent on a good structural backfill compacted around the pipe at say 95 % standard Proctor and loosely compacted material above the crown for about 600 mm in the case of multiplates. In contrast the reinforced concrete pipe because of its rigidity and less deflection characteristics of the pipe material can suffice without the expensive backfill required for other pipe types excepting steel.

Anyhow, performance of pipes as well invoke other considerations apart from backfill for example undermining, erosion. In those cases a CSP pipe would fail much more dramatically than the reinforced concrete pipe since if its backfill is eroded then it collapses as a tin can.

At that stage of the game for both pipes, their functionality would be totally compromised.

 

[SlideRuleEra]

rconner - Perhaps I am misreading the original post, but the question seems to be about lack of cover over the pipe - nothing is said about a problem installing bedding. For this reason, I assume that the pipe can be correctly bedded.

Where I work, coastal South Carolina, a high water table (usually assumed to be the surface of the ground) forces drainage pipes to be installed with very little cover, often less than the 12" specified in this post. On electric utility plant sites in this area we have used Class III and IV concrete pipe for numerous applications including aggregate haul roads used by large off-road trucks carrying coal waste products to on-site landfills. With proper bedding (but little cover), these pipes have performed for decades without problem.

In other applications, with rigid pipe, the surrounding soil is a liability rather than an asset:

Buried, pile supported pipelines going under roads. After a few years, you start to feel the "bump" as your car goes over the pipe crossing; as more time passes you can see the "bump". The buried, pile supported pipeline has remained at a constant elevation - the ground, including the road have settled. The rigid pipe is having to support the road and the traffic passing over it - yet, they can do it.

Needless to say, I am a big fan of rigid pipe, including RCP, steel, & DI

http://www.SlideRuleEra.net

 

[LCruiser]

Talking about RCP vs. CMP or HDPE is apples and oranges. The latter are flexible pipe and laterally compress the adjacent soil to develop structural integrity. So, the deeper one goes the more the lateral support helps, vs. the shallower point load scenario.

 

[civilperson]

The list of materials made by Stoddardvilla is probably correct as to material strength of equal thickness, however it is wrong to say DIP pie with 0.8" of wall thickness is stronger than RCP with 3.9" of wall thickness. I stand by my original statement. The strongest pipe for this application is Class V RCP. Use of flowable fill is better than the best class bedding listed. I used this pipe under taxiways for Boeing 747 traffic with only 15" cover to pavement surface and no failures have been reported. Compared to heavy trucks the wheel loading of a landing gear is much greater with tire pressures on military jets over 240 psi.

 

[rconner]

There can of course be healthy debate as to what exactly constitutes the "strongest" piping system. There is no doubt that concrete pipe has great ring strength and additionally has provided utility in many applications; however, it also possesses VERY little ductility when the strengths are locally exceeded and also must be quite fortified with steel if it is to function as an effective beam in any sort of bridging (or heaving?) or tensile stress loading. Concrete material in and of itself is less suited to handle tensile loading than steel or ductile iron, and could have issues in other applications.
While many of us know all these different types of pipes are "apples and oranges", unfortunately to an unknowing or unwary buyer they might just be "pipe X" and "pipe Y", at $X' and $Y' material cost per foot, respectively. [Consider the case of poor homeowner who chimed in near the latter part of the parallel thread regarding also a shallow culvert application though apparently residential at

http://www.eng-tips.com/viewthread.cfm?qid=155551&page=1

– there was apparently at some point some need to replace an existing concrete culvert that was for some reason somehow in a couple pieces, and this was done in one or more permutations reportedly by a good reputation installer with some sort of “black plastic” pipe. She said (while apparently the new plastic pipe itself didn’t break) her new asphaltic driveway unfortunately cracked within six months over the new pipe. What’s a lady to do?? It would appear to me the whole soil/pipe/pavement system should be considered along with practical/expected installation/inspection field quality, not just the alleged “strength” or “flexibility” of the pipe?]
Incidentally, civilperson is quite correct that Boeing 747 live loading is much larger than e.g. H20 truck loading; however, I would only like to add that it is my understanding ductile iron and I’ll bet also steel pipes have also been successfully installed under taxiways etc. (and I believe an external loading design procedure is even available from DIPRA for ductile iron pipes upon request for this application). Everyone have a good weekend!