Re-enforcing a Big Culvert

[Syncro]

We have a 6' steel culvert out at the ranch that is plenty strong for tractors, bailers, and my backhoe, but it had me a little concerned about driving a fully loaded mixer truck over it. The more I thought about it the more I envisioned a mishap with 11 yards of ready mix along with a very expensive truck breaking through. To beef it up I contemplated various methods, one was to use railroad ties, or other heavy timbers but re-enforced concrete seemed like the best solution.

Attached are a few pics of the job.

Pic #1 setting the #4 steel, we used plenty of it 12" o/c each way.

 

[Syncro]

Pic #2 shows the 3" pipe chases we laid at the bottom for furure use. 3 on one side and 1 on the other. Also evident are the 4" vinyl post cut-offs we encased in the concrete for future railings. The steel was ran about 16" past the forms on each side for widening the bridge at a latter date. Average depth of the slab was 9 1/2" with the steel placed mid-way in the 6 sack with fibre concrete.

 

[Syncro]

Pic #3 shows the slab before we added the railings and final road base approach grading.

 

[Syncro]

Pic #5 is the finished bridge. Its a pretty stout crossing now and I'm much more confident about driving any size truck over it.

 

[Syncro]

Pic #6 Using my trusty MF 1240 CUT to spread road base for the bridge approaches. Small tractors like that are handy for tight jobs and the reduced weight makes driving on fairly new concrete all the safer.

 

[pekabu]

Pic #6 Using my trusty MF 1240 CUT to spread road base for the bridge approaches. Small tractors like that are handy for tight jobs and the reduced weight makes driving on fairly new concrete all the safer.

The view in this picture is beautiful!

 

[3RRL]

Oooh Syncro,
That turned out super nice! No worries about that anymore. Nice job.

 

[EddieWalker]

I wasn't understanding your situation until I saw the pictures. Is there a formula for how much dirt is supposed to be on top of a culver for maximum strength?

I like your solution and the final results!! That concrete will spread the load and handle anything there is!!!! Very nice.

You still have me a little confused about the 16 inches of rebar off the sides. If you make it wider, will you relocat the railing? Are the posts removable so you can use the bridge at full width at certain times and then replace the posts to have it narrow again? I don't understand this.

Or are you going to pour a wall that goes down to the culvert and ties into the pad to form sides to protect the material under the pad from washing out during heavy storms and flooding??

You did a really nice job and it was fun to see you pictures.
Thanks,
Eddie

 

[HomeBrew2]

Wow!, the ditch tenders in your part of the country sure are pretty!

 

[Syncro]

.....Is there a formula for how much dirt is supposed to be on top of a culver for maximum strength?

You still have me a little confused about the 16 inches of rebar off the sides. If you make it wider, will you relocat the railing? Are the posts removable so you can use the bridge at full width at certain times and then replace the posts to have it narrow again? I don't understand this.

Or are you going to pour a wall that goes down to the culvert and ties into the pad to form sides to protect the material under the pad from washing out during heavy storms and flooding??

Eddie

The usual rule of thumb is 1/2 the culvert diameter for ground cover. 12" dia = 6" cover etc.

The railings are removable. I placed 16" long post sleeves in the concrete and have pieces of sch 40 4" conduit that fit inside these bases and up into the posts, so its solid but easily pulled up and off for wide equip. I just ran a 16' wide swather over my 15' wide bridge by taking off the railings.

You are right about rain washing away the base under the slab. I'm going to extend the slab to the edge of the 20' culvert and also pour a head wall at each end down below the water line, thats the reason I left the re-bar stubs to connect the new steel. When I do that I'll put in permanent railings and fill in the existing sleeves.

 

[MikeD74T]

Nice looking job !!! I'd make one recommendation for future work. Reinforcing rods in the middle of a thick pour loose effectiveness as the slab gets thicker. I've poured several bridge decks on state & interstate highways. The thickness is 8-10" with a double rebar mat 12" on center - one 2" from the bottom & the other 2" below the top. Rebar varies from #4 to #6 depending on span/slab thickness. You may experience breaking in the middle from the ends bending down if the fill settles.

 

[Syncro]

Nice looking job !!! I'd make one recommendation for future work. Reinforcing rods in the middle of a thick pour loose effectiveness as the slab gets thicker. I've poured several bridge decks on state & interstate highways. The thickness is 8-10" with a double rebar mat 12" on center - one 2" from the bottom & the other 2" below the top. Rebar varies from #4 to #6 depending on span/slab thickness. You may experience breaking in the middle from the ends bending down if the fill settles.

Thanks Mike, that is interesting, wish I'd have known that before. Still, I think it will distribute the weight (I hope!) Now that I think about it a double layer of steel makes a lot of sense. Next Time!

 

[Iowachild]

Very good looking project and I agree pekabu, the view in pic #6 is magnificent!

 

[CharlieTR]

Looks like a great job!
I have a ditch I was planning on building a bridge to allow direct access to the back 40 acres. Now I need to drive about 1.5 miles to get across.
After seeing this I think a culvert would be a faster and cheaper alternative.
My only concern is the high fast water in a flash flood washing away the sides around the culvert. Water does wash up much higher and wider than the ditch. Have yo had any problems with high water?

Also not sure if two pipes are required.

Thanks

 

[Syncro]

Looks like a great job!
My only concern is the high fast water in a flash flood washing away the sides around the culvert. Water does wash up much higher and wider than the ditch. Have yo had any problems with high water?

Also not sure if two pipes are required.

Thanks

I don't have fast moving water, but I'm still going to pour a solid concrete head wall at each end of the culvert. That will help keep the whole thing together. Fast moving water can be a pretty powerful force though, and if you have a severe enough overflow it could still wash away. As far as using 2 smaller culverts, if it were me I'd favor one larger one to reduce blockage from debris that may wash into it.

Have fun.