Bridge building!

[aighead]

Hey Gang, I've previously posted about a pretty small bridge I've built over my small creek that goes to the back couple acres of my yard. Well, I have been offered a decent pile of concrete block and I already have some that the previous home owner so sweetly stored in the fence-row. My question is has anyone built a bridge out of this material and would you trust driving a backhoe over it when it's complete? The picture below is the bridge I currently have, but picture it covered in packed dirt that likes to fall apart off the sides.



The plan would be to dig up the bridge that is there, plus some, to get a decent spot to lay the blocks and fill them with dirt/gravel/concrete(?), probably try to keep the same pipes I have there but make the layout a bit nicer, then fill the empty space with more dirt/gravel/concrete, then lay additional blocks on top probably a couple layers high, and maybe re-cover that with dirt (though I think it'd be nicer if it was just the block to drive over). I assume that if I pack the empty space between the leading and trailing stacks of block and the pipes then I could pretty securely stack block over the pipes so it's all sturdy enough to drive over, but maybe I'm wrong... I just realized that it can't be dirt that would just wash away.



What am I not thinking of?

 

[redneckracin]

If I may make a suggestion, One big pipe flows better than 3 smaller pipes however, if you can't get enough cover to protect the pipes (I don't know what material that the are made of. I'm assuming they are plastic.) I would lay the pipes flat to get more cover over them. If you "pave" over the pipes with the blocks, that's all the better, it should help spread the weight out plus make the driving surface more durable!

 

[treemuncher]

Culverts, unless they are really large, tend to get plugged and overflow around and over the structure and cause failure. Have you considered building a shallow (low) water crossing instead? You could still use the block for that. I would fill it with a dense grade limestone gravel. I normally just use limestone rip-rap 6's & 8's then topcoat with #3's to fill the larger voids. Works well for most high water events and will not plug up. I learned this technique at a Loggers BMP tech day. It's much easier than culverts and won't wash out. If you need to cross the creek during high water events, this may not be the best choice.

See this link for a fancier design. https://www.conteches.com/knowledge...sing-design-use-of-articulated-concrete-block

 

[DMiller]

We have five Terrace Head crossings on our drive, two have larger 24" culvert drain pipes, thought could get by with slow rate low water crossings on the last three as were very low rate of angle, was terribly incorrect. After re-rocking the road three times and grading several in between added 12" culvert pipes to those and has been enough until some 3-5" rains in less than 8 hours and they do choke rapidly with debris in the farm fields. May soon end up installing 24" to all three of these yet. The original lay was terraces directed water to their end at this point with a grassy steady grade area for runoff, the terraces were extended to allow the drive to work less erosive blowouts.

 

[aighead]

Thanks guys! Here's a new thought... What about removing the fill and pipes entirely and either finding some steel plates to brace in the sides and top (for the top blocks to sit on) or concreting the whole thing together? I'm pretty positive that I couldn't drive the backhoe over it just concreted but maybe I could figure out something there too..

@redneckracin The single big pipe is ideal and now that you mention it I've forgotten several times that I do want to go that route. I tend to never want to spend money on that sort of thing, so I usually use junk laying around. I think I saw big pipe like that for around 3-400 bucks so it's almost manageable and would definitely be better than the 3 12-16 inchers currently in there (one concrete, two very thin pvc, all clogged up a bit).

@treemuncher I'd never thought about a shallow water crossing... I'll take a look at the article you linked to. It's an interesting idea but I'm not sure it suits my needs. It would be significantly more steady and sturdy I think.

@DMiller That sounds like a lot! I now feel fortunate that I'm not messing around with that much!

 

[redneckracin]

Those low water crossings can be pretty stout, Ive seen several in WV that were either just large stone (<6") and I've also seen some that had several small pipes that were concreted together to keep them in place, but let high water flow overtop and not take the pipes with them. Hopefully you have a solid bottom and not feet of silt to work with though.

In regards to the "bridge" How big of a span would you be shooting for? If its less than 5', some heavy timbers may work out just fine.

 

[JBrady]

My only suggestion is just to know very well what your crossing CAN look like in different weather situations. I have several crossings on my place. Right now all of them are dry, however, I have seen them 4' deep with water and 30' across. No culvert in the world is going to handle that. As an old dozer operator told me one time, "that valley didn't just get there by happenstance!".

 

[aighead]

While I like the low water crossing design a lot (and that article is really well written) I don't think it'll work for me unless I were to really do some extensive creek regrading. I take my small mower across the bridge more that the backhoe and it would be axle deep pretty quickly. If it were just the backhoe I think it'd be ideal.

I can't seem to find a decent picture of the creek at its fullest. Below is one that is an overflow before I redid it and this was a fairly normal level in the spring with a couple major overflows a year, as seen by my crude drawing, the dark blue line is where the creek runs, the light blue is the flooding in the lowlands of the yard.


The bridge is only "crossing" a section maybe 8-10 feet wide, if I regraded a bit it may not be that much. However, to @JBrady 's point it's not uncommon for the creek to fill and overflow, where in that area it could be running pretty hard at around 3-6 feet deep, though likely only for a day or two. Normal spring time I'd say it's 6 feet wide but only a foot or two deep, but running. We've had times of heavy rain where there is a low section of the yard that will be ankle deep for maybe 100 feet wide from the creek and maybe 200 feet of lateral creek bank.

 

[DMiller]

Based on the above Flow picture, you need a 'Real' bridge. No low water crossing, no culverts. Set up abutments on each side two to three feet Above and at least as much below grade. Ramp UP onto bridge of sufficient steel members to support four times the expected weight to cross and establish a decking either wood, concrete or steel flooring. If MUST continue down a path of Culvert pass thru, then buy Three of at least one and one half times the internal ID of the one being overloaded set side by side and incorporated into a crushed stone retention berm.

 

[terex herder]

There are also shallow water crossings that have a small culvert buried. That way you have a dry crossing most of the year. The point to a low water crossing is to build a structure that can withstand the current when its flooded. As long as you can handle the dip at the bottom, its the cheapest and most long lived solution.

 

[Vetech63]

While I like the low water crossing design a lot (and that article is really well written) I don't think it'll work for me unless I were to really do some extensive creek regrading. I take my small mower across the bridge more that the backhoe and it would be axle deep pretty quickly. If it were just the backhoe I think it'd be ideal.

I can't seem to find a decent picture of the creek at its fullest. Below is one that is an overflow before I redid it and this was a fairly normal level in the spring with a couple major overflows a year, as seen by my crude drawing, the dark blue line is where the creek runs, the light blue is the flooding in the lowlands of the yard.

View attachment 223416
The bridge is only "crossing" a section maybe 8-10 feet wide, if I regraded a bit it may not be that much. However, to @JBrady 's point it's not uncommon for the creek to fill and overflow, where in that area it could be running pretty hard at around 3-6 feet deep, though likely only for a day or two. Normal spring time I'd say it's 6 feet wide but only a foot or two deep, but running. We've had times of heavy rain where there is a low section of the yard that will be ankle deep for maybe 100 feet wide from the creek and maybe 200 feet of lateral creek bank.

View attachment 223417

I’m seeing a nice spot for my RV to sit for a month!

 

[aighead]

Thanks guys, @DMiller what you are proposing sounds right just expensive! I would imagine this will be the end result though I do like @terex herder 's buried culvert idea too...

Come on out @Vetech63 , rent is somewhat affordable!

 

[DMiller]

Build it Correct ONCE or rebuild it in imaginative ways enough times to have paid for the Correct style ONCE.

 

[crane operator]

I’m seeing a nice spot for my RV to sit for a month!

Ha! Surely oklahoma has too many broken machines- you can't take a month off work! I know of at least one trailer project.....

 

[aighead]

@DMiller now you are getting my style! I'm too poor to do it right the first time, so, unfortunately I have to make do...

 

[crane operator]

I set this premade mat material a few years ago. It actually has cables cast into the blocks to tie them together. Then filled with crushed stone. It has a geo fabric under it. I think you are trying to do something similar with just the blocks? Keep the culverts in, and then put the concrete blocks on top and if the creek gets high- it just goes over the blocks?

 

[aighead]

That's correct @crane operator though I wish I had a scale model of what you are doing there... Looks pretty slick!

 

[treemuncher]

Another cheap method of bridging is a used semi flatbed trailer. Knock out the axles and landing gear and place it on supports. Old flatbed RR cars should provide an even heavier load bearing amount.

Remember that the fastest and most powerful water flow is at the surface. The slowest flow is always at the bottom of the river/creek and will have the least amount of hydraulic pressure on an obstruction to flow. This, and failure to clog, is why shallow crossings work well but not as a daily bridge. You might also be able to find used concrete slabs that you could place. I've sold a number of former concrete steps from a federal installation demolition job for shallow water crossing building blocks for local farmers. 4'x8'x6" concrete slabs bear plenty of weight and will not shift easily.

I've never forgotten having to cross a semi trailer bridge on a customer's hunting property. It was 8' wide max and 12' above the ditch. I don't think that I had more than 12" of tire on that bridge on either side, with more than that hanging off each side, with very limited visibility on the Barko 937. I crossed it twice without issue other than heavy sweating and rattled nerves. I never did see the "bridge" flex as I crossed it with that 40k lb machine.

 

[DMiller]

Biggest issue with any solid placed In the flow is Scour, end up anything loose around the solid materials gets washed away and the entire solid structure blows out.

 

[aighead]

@treemuncher a flatbed sounds great! I would have never thought of that! I don't know what one goes for but I love the sound of it, a 20 footer would work beautifully! Also, I got butterflies in my stomach at your story of driving over one, so sketchy! I took my backhoe to my buddy's house and loading it onto the trailer felt the same. I did a pretty serious wheelie upon approach and while I don't think they were it felt like the tires were just barely on the bed. My current bridge is also very narrow and likes to crumble a bit on the edges so I'm pretty nervous I'll go over one of these days. Luckily, I don't have to drive over it very often but when I do I lower the outriggers as much as possible and drive over quickly!

@DMiller I think this is my biggest concern too... Our current bridge is holding up well but we haven't had a yard flooder since it's been built and it already loses a bit off the sides just about anytime it rains. We have a fair amount of rock and chunks of concrete packed in there and while it's solid I've seen enough water flowing through that area to make me nervous about it.