Pipe Arch culvert... any experience?

[Dadnatron]

I have been putting in a new road, and finally have reached the last 2 places which will need culverts.

One is a relatively shallow but wide ditch, approximately 18" deep by about 8' across. I have kept it very shallow, flat, and wide as that is the best way to prevent erosion. Typically, it has only a little bit of water which could easily be handled by a 10" culvert about 90% of the time. HOWEVER, about 2-3 times each year, we have a deluge which will result in the entire ditch being full. Also, this ditch runs along about 100yds of my new road, before it dumps out to the side and away.

I need to add a culvert to connect my new road to an old access point and therein lies my issue.

I need something which will handle the high water, but I need it to be relatively shallow depth given the grade and adjacent road height. Overall, we figure an 18" culvert will handle the load, however, I don't have 18" of depth to work with, and cover it adequately. I looked at putting 2 culverts side by side, but putting in 2-12" culverts does not provide the amount of even 1 18". Close, but not quite. And I add in the difficulty of putting 2, in line culverts side by side, in such a way that they don't wash out. I know I can use concrete and build a wall, etc, but I am trying to keep this as simple and 'unobtrusive' as possible.

So I found a 'pipe arch' which sounds like it will work, but I have spoken to no one who has used them before. Typically, it appears, they are used in more major road construction and are larger in diameter, ie several feet. But they do make an 18" pipe arch, which is basically an 18" corrugated metal culvert 'squashed down' to a semi-oval 12" height. Apparently it maintains the capacity of the 18" culvert but takes up the 'height' of a 12". This would allow me to install it with adequate cover in place of a 12" culvert but provide the needed capacity.

In reading about installation, it appears to be pretty standard, just must be sure to adequately compact soil below the lower curvature, then install with normal compaction and cover.

But I wanted to ask whether anyone here has used them and has anything more to offer in thoughts and/or recommendations in their use or avoidance.

 

[ovrszd]

I've put in hundreds of culverts but never had to use one. I see no negative. They are designed for situations like yours. I'm guessing they are pricey?

 

[blacklion66]

After it is installed, will gravel fill stop it from squashing down under a heavy load? Me thinks not.

I think if I had to use something like that I would pour cement on both sides and then gravel over it.

If you had the use of a excavator you could flatten your own culvert rather than buy it ready
squashed ☺

 

[bcp]

Precast box culvert?

Bruce

 

[fried1765]

I have been putting in a new road, and finally have reached the last 2 places which will need culverts.

One is a relatively shallow but wide ditch, approximately 18" deep by about 8' across. I have kept it very shallow, flat, and wide as that is the best way to prevent erosion. Typically, it has only a little bit of water which could easily be handled by a 10" culvert about 90% of the time. HOWEVER, about 2-3 times each year, we have a deluge which will result in the entire ditch being full. Also, this ditch runs along about 100yds of my new road, before it dumps out to the side and away.

I need to add a culvert to connect my new road to an old access point and therein lies my issue.

I need something which will handle the high water, but I need it to be relatively shallow depth given the grade and adjacent road height. Overall, we figure an 18" culvert will handle the load, however, I don't have 18" of depth to work with, and cover it adequately. I looked at putting 2 culverts side by side, but putting in 2-12" culverts does not provide the amount of even 1 18". Close, but not quite. And I add in the difficulty of putting 2, in line culverts side by side, in such a way that they don't wash out. I know I can use concrete and build a wall, etc, but I am trying to keep this as simple and 'unobtrusive' as possible.

So I found a 'pipe arch' which sounds like it will work, but I have spoken to no one who has used them before. Typically, it appears, they are used in more major road construction and are larger in diameter, ie several feet. But they do make an 18" pipe arch, which is basically an 18" corrugated metal culvert 'squashed down' to a semi-oval 12" height. Apparently it maintains the capacity of the 18" culvert but takes up the 'height' of a 12". This would allow me to install it with adequate cover in place of a 12" culvert but provide the needed capacity.

In reading about installation, it appears to be pretty standard, just must be sure to adequately compact soil below the lower curvature, then install with normal compaction and cover.

But I wanted to ask whether anyone here has used them and has anything more to offer in thoughts and/or recommendations in their use or avoidance.

View attachment 580291

Per pipe tables: For 15" - 30" elliptical corrugated steel pipe you will need a minimum of 12" cover for private installation.
More cover is required if it is a commercial installation.
I suspect that you can buy 2-12" culverts for something less than one 18" elliptical.
The total area of the 2-12" culverts is only 11% less than the area of the 18" elliptical.
The best solution actually might be 2-15" culverts, and.... maybe separated by a few feet if possible.

 

[stevewarner1957]

I’ve used many in road entrance situations. They are great when you can’t use round pipe and get the needed cover over the top of the pipe. In shallow flow line situations the ADE (Arch Diameter Equivalent) pipe are great. You can get 15” diameter pipe flow with 12” pipe height but it’s 18” wide, great for wide shallow ditches.

 

[oosik]

I have, in my travels, seen ONE such arched culvert. It was used where a private driveway entered onto a county road. As I remember - its somewhere down is SE Idaho - not that its location makes any difference. Obviously - the culvert was expensive - each side of the driveway, at the culvert, had been "decorated" with native stone set into the dirt embankment. Some private party was very proud of this culvert arrangement.

Now - those box culverts that Bruce(bcp) is showing. One of the railroads that pass thru this area use those things quite often. They serve a multiple purpose - with a poured, flat concrete bottom they allow cattle to pass from one side of the railroad to the other and of course if there is ever enough rain - they pass water. Obviously - somewhat taller than bcp has pictured.

Certainly - there must be specifications for installation and load capacities on such a culvert.

 

[CobyRupert]

Typically, it appears, they are used in more major road construction and are larger in diameter, ie several feet. But they do make an 18" pipe arch, which is basically an 18" corrugated metal culvert 'squashed down' to a semi-oval 12" height. Apparently it maintains the capacity of the 18" culvert but takes up the 'height' of a 12". This would allow me to install it with adequate cover in place of a 12" culvert but provide the needed capacity.
]

I don't think a squished 18" maintains the same capacity as a round 18".

Playing with numbers:
(2)-12" diameter round culverts have a total area of 226 sq. inches.
A 18" diameter round culvert , with an area of 254 sq. inches, can handle more water.

Note that 18" round culvert has a circumference of 56.5".

If we take that same 18" culvert and squish that 56.5" circumference down to 12" high, we see it would be 23" wide
(circumference of an ellipse - Google Search)

A 12" high by 23" wide ellipse has an area of: 218 sq. inches.
area of an ellipse - Google Search

This is less than an 18" or (2)- 12" round culverts.

 

[DJ54]

I've helped put in more than several of those over the years working at ODOT. The easiest way to get compaction down under, and along side the pipe is to use sand, and heavily flood it with water, to wash the sand down around it. We normally put a load of #2 limestone on each end to keep the sand contained, but, let the water out. I can't emphasize enough, that it needs to be flooded to the point, where you get a slight ponding of water, not just run a water hose on it for a few minutes. On a shallow pipe, you need just enough to cover the pipe, the rest is most generally 67D/411 crushed limestone, compacted to the top, in no more than 8" lifts. On a shallow pipe, a plate tamper works great. It's a good idea to stake the pipe down, to keep it from floating.

Another way, is to use a low strength grout. Basically, a 1, or 1-1/2 bag per yd., and sand only concrete mix. That mix will cost you pretty much the same as regular concrete, but saves a LOT of work. That too, we put #2 limestone at the ends to let the water perk out. Again, using this method, the pipe needs to be held down, to keep from floating. We most generally used T-posts driven in at a 45 degree angle, contacting the pipe in an X fashion, over top, and wired together at the top, to hold them in place. Drop the grout in directly on top of the pipe slowly, and let it run down around the sides. It needs to be pretty wet, and sloppy. If fly ash is available, and added, it will help it flow, and run. If not, no big deal. Use a concrete vibrator, and just enough to flow the grout around the pipe nothing excessive, or the grout will go under the pipe, floating it. You only need enough to cover the pipe a few inches, then finish to the top with compacted 67D (3/4" to dust) limestone, or whatever is available in your area.

The ends can be dressed with the appropriate sized stone, for erosion control, if it tends to get that wild.

 

[ovrszd]

The biggest inhibitor of flow is wall resistance. This is partly why the larger culvert seems to gain more flow than the size ratio difference would indicate. For this reason we use dual wall plastoc culverts. They are smooth bore.