Need Span Load Advice for Small Bridge

[Natty Bumppo]

I am trying to cross a small brook on my land with my JD 990. It weighs 5,500 lbs. The brook is shallow and barely runs during the summer, but can run quite vigorously in the spring. A culvert is not an option. The land is swampy and wet. Fording the river is possible but just destroys the banks.

I would love to be able to use PT 4x6's for stringers. The total span is 8' but really with a foot and a half of 4x6 on each end resting on the ground, the actual span is on'y about 5 or 6'. I tried looking up some kind of a load calculator but found nothing that didn't just confuse the heck out of me.

I was hoping somebody could tell me if I could get away with 4x6's. Price isn't an issue....I don't care if I had to use 5, 6, or 7 of them. If not 4x6's...if I doubled up some 2-by boards what's the smallest dimension I could use...2x8's? 2x10's?

Thanks in advance. It's a small brook...but it's turning out to be a pain in the arse to cross.

 

[Ben.MN/WI]

If you go with a bridge, you'll likely need to set your boards on some type of concrete bases/supports. Even if you have wood that is strong enough to hold 5000 pounds, the whole bridge could collapse if you had it sitting on bare dirt which could shift or collapse under load. Load calculators require a lot of assumptions, so your bridge could have plenty of strength on paper only to fail when you drive across it. You could build and test a bridge in your yard or driveway pretty easily by just building it a foot off the ground. Then if it fails you likely will not be injured.

You might save some money (and potentially your tractor) by bringing in a load of rock to create a creek crossing there. 6" of packed down rock would makes a really nice crossing that will last longer than the best wood bridge.

 

[j-bird]

I try not to mix wood and equipment.....too many variables. Without using engineered timbers you have little idea of what sort of strength you are actually getting. Then you take into account how quickly (even pressure treated) they can degrade and I just try to avoid the entire thing! I would look at ribbed poly culverts or steel stringers (I-beams or wide flanged beams). We used a 48" ribbed poly culvert pipe on my place when we did some logging and they ran all sorts of stuff over it without an issue and it will last my lifetime. They are pretty light as well. We simply tossed it into the ravine and back filled with dirt and gravel and have been great ever since. With water flow you will have to do some digging to make sure you get the water going thru it and not around it. Proper support for a bridge as Ben speaks to is also important. And I like his idea of testing anything you wish to try at a far safer height as well first. I know wood is a great building material, but there are reasons we don't have many wood bridges any more.

 

[Natty Bumppo]

Thanks Ben.MN/WI and j-bird. I hear what you're saying. The brook only has about 14 to 16" of drop to it below grade. I am basically trying to cross a very flat swampy area that sits between my house and my land no matter which direction I travel. The trail leading to the brook is a wet swamp....I have had to lay down 90 feet of spruce and fir logs across the trail just to support the weight of my tractor without leaving massive ruts. It's a lot of labor...but it works just fine.

Ben, the packed rock idea sounds good. I am just not sure if that just disappears into the black muck when I try driving over it.

I am going to look into ribbed poly culvert. I suppose I could find a 24" piece and set it in the stream bed so it's below grade a bit an then bring in dirt and fill. Maybe even set two side by side.

Thanks.

 

[Ben.MN/WI]

I have experience with the muck found below black spruce swamps and that stuff sucks. But it will firm up if you keep sinking enough rocks into the endless goop. it works best if you can scoop out some of the goop and replace with rocks and really pack them down.

I'm impressed that you could lay down enough logs to get a tractor 90' in that stuff. I've had to create my own spruce and tamarac boardwalks in some areas in my swamp to get my ATV in there. it's a lot of work, but it sure is nice once done. I couldn't imagine doing that for a tractor though.

 

[MRBB]

are you sure your even allowed to do this?
I ask, due to here in PA< its NOT even legal to do, without a huge amount of paperwork and approved plans
NOT getting the paperwork here can lead to HUGE fines, ten's of thousands of dollars in fines!
wet lands, or not, here crossing any waterway even a small creek is a night mare to make a bridge , even a walking path one, never mind one to drive across?
I just don't want to see anyone get into trouble, so, food for thought here!

THAT being said, ever look into maybe finding a older tractor trailer and using that as a frame work?? to lay across?? then add material to floor it?


some of them are 50 ft long and should hold the weight rather easy?

 

[Tree Spud]

I am trying to cross a small brook on my land with my JD 990. It weighs 5,500 lbs. The brook is shallow and barely runs during the summer, but can run quite vigorously in the spring. A culvert is not an option. The land is swampy and wet. Fording the river is possible but just destroys the banks.

I would love to be able to use PT 4x6's for stringers. The total span is 8' but really with a foot and a half of 4x6 on each end resting on the ground, the actual span is on'y about 5 or 6'. I tried looking up some kind of a load calculator but found nothing that didn't just confuse the heck out of me.

I was hoping somebody could tell me if I could get away with 4x6's. Price isn't an issue....I don't care if I had to use 5, 6, or 7 of them. If not 4x6's...if I doubled up some 2-by boards what's the smallest dimension I could use...2x8's? 2x10's?

Thanks in advance. It's a small brook...but it's turning out to be a pain in the arse to cross.

I agree with Jbird ... even putting supports in for the bridge would be dangerous unless you have firm foundation cement piling into the soil ... which you won't have. Do you really want to risk rolling a 6k lbs tractor because one side of your bridge gave in?

Consider a Tennessee mud bridge ... lay down from 10' on either side of the bank, a 6-12" layer of rock. Softball to hardball size rocks filled in with gravel. Had a buddy do this on a couple of streams on his place and they worked very well.

Or do the culvert. If flows are low you could get away with 2-3, 10" culverts putting dirt & gravel over them.

 

[rocksnstumps]

Some guidelines to refer to on sills and span options. A railroad tie on each side spiked with 4 ft rebar on each span would probably work decent for a sill. If it's total loon $h&t might have to tie several together each side. If this little stream or brook shows up on any maps better consider how to approach a build. My buddy got a culvert put in and it was all handled by a snowmobile club. No open trail for the rest of the year however so he was ok with it. They even paid for gravel on the swampy part leading into the crossing.
https://www.fs.fed.us/eng/bridges/documents/snowcat/index.htm

 

[Natty Bumppo]

I have experience with the muck found below black spruce swamps and that stuff sucks. But it will firm up if you keep sinking enough rocks into the endless goop. it works best if you can scoop out some of the goop and replace with rocks and really pack them down.

I'm impressed that you could lay down enough logs to get a tractor 90' in that stuff. I've had to create my own spruce and tamarac boardwalks in some areas in my swamp to get my ATV in there. it's a lot of work, but it sure is nice once done. I couldn't imagine doing that for a tractor though.

Great input Ben. Thanks. I live on a 2,000 plateau called The Drowned Lands...a spruce, fir, and tamarack swamp. My house is on high ground and my land and food plots are on high ground. If I can cross this low drainage swamp I am on nice dry land and the soil is beautiful. I have a few other ATV trails and I have had to use the spruce and fir logs on them all. It is labor intensive, but it works just fine. As I work the land and do TSI and make food plots and trails I take down all kinds of spruce and fir and then use those for the trails. For this one trail I am making for my tractor I am using much bigger spruce and fir....trees that are 8 or 10" DBH.

Random side note.....I am a WWII buff and in WWII the Germans did this very same thing in Russia when the roads turned into a quagmire. Hundreds of miles of spruce and fir lined roads that supported tanks. When I am out there spending huge amounts of time and labor cutting down trees and hauling them to my trail I imagine the Germans doing it for 100 miles of road and then my little ATV and tractor trails don't seem too bad.

 

[Natty Bumppo]

are you sure your even allowed to do this?
I ask, due to here in PA< its NOT even legal to do, without a huge amount of paperwork and approved plans
NOT getting the paperwork here can lead to HUGE fines, ten's of thousands of dollars in fines!
wet lands, or not, here crossing any waterway even a small creek is a night mare to make a bridge , even a walking path one, never mind one to drive across?
I just don't want to see anyone get into trouble, so, food for thought here!

THAT being said, ever look into maybe finding a older tractor trailer and using that as a frame work?? to lay across?? then add material to floor it?


some of them are 50 ft long and should hold the weight rather easy?

Thanks for your thoughts. Appreciate it. A few things....there are bridges all over the place here in NW Mass. Snowmobile, ATV, logging, hiking...maybe it's a different culoture and climate of bridges and bridge building. Maybe less regulation? I am a member of several clubs...snowmobile and a ski club...and we routinely make bridges in the back country with Mass. DCR approval with basically just a verbal approval.

The creek I am trying to cross is so small, that I don't even think both the front and rear tires of my tractor would be on the bridge at the same time. The trailer idea I did read about and consider. Just way too big.

 

[Natty Bumppo]

I agree with Jbird ... even putting supports in for the bridge would be dangerous unless you have firm foundation cement piling into the soil ... which you won't have. Do you really want to risk rolling a 6k lbs tractor because one side of your bridge gave in?

Consider a Tennessee mud bridge ... lay down from 10' on either side of the bank, a 6-12" layer of rock. Softball to hardball size rocks filled in with gravel. Had a buddy do this on a couple of streams on his place and they worked very well.

Or do the culvert. If flows are low you could get away with 2-3, 10" culverts putting dirt & gravel over them.

Great thoughts Treespud. Spot on. I am heading downtown today to source some poly culvert.

 

[Natty Bumppo]

Some guidelines to refer to on sills and span options. A railroad tie on each side spiked with 4 ft rebar on each span would probably work decent for a sill. If it's total loon $h&t might have to tie several together each side. If this little stream or brook shows up on any maps better consider how to approach a build. My buddy got a culvert put in and it was all handled by a snowmobile club. No open trail for the rest of the year however so he was ok with it. They even paid for gravel on the swampy part leading into the crossing.
https://www.fs.fed.us/eng/bridges/documents/snowcat/index.htm

Great link. Thanks.

 

[Boll Weevil]

Built a crossing at a place much like you describe by placing a base of logs lengthwise in the ditch, a section 20" corrugated metal culvert atop the base, then stack logs lengthwise on top. Covered it with dirt, sowed grass, and it now looks like a land bridge. Low flow like you describe just seeps/trickles through the logs while higher flow may utilize some of the culvert pipe.

 

[S.T.Fanatic]

We built a bridge a few years ago out of used wood telephone poles. We layed down 4 poles and had 2 more cut into 3" thick planks for the deck. It supports my brothers Kabota just fine and its heavier than the JD mentioned.

The span is prob about 10' and is sitting on an old bridge foundation that is little more than stacked limestone and mortar. I wouldn't be afraid to drive a dozer across it.

 

[MRBB]

Thanks for your thoughts. Appreciate it. A few things....there are bridges all over the place here in NW Mass. Snowmobile, ATV, logging, hiking...maybe it's a different culoture and climate of bridges and bridge building. Maybe less regulation? I am a member of several clubs...snowmobile and a ski club...and we routinely make bridges in the back country with Mass. DCR approval with basically just a verbal approval.

The creek I am trying to cross is so small, that I don't even think both the front and rear tires of my tractor would be on the bridge at the same time. The trailer idea I did read about and consider. Just way too big.

they can cut down a frame from a trailer pretty easy these days, plasma cutters and zip right thru it

I belong to a few snowmobile culbs ,a nd all I know of need permmission to cross any flowing water way

again things sure could eb different were you are
but here in pa, if the water moves, it doesn't matter if it 6 inches across or 600 ft

we have a small spring fed creek behind our cabin, its about 3 ft wide, but pending weather, it can grow in high rains or snow melts
back in the 60's the older guys in hunting camp built a 12 ft long walking bridge across it, up about 6 ft above things so in high water it still worked!
well a few yrs back(early 2000's, bridge was getting very unsafe, so we re built it, exactly like it was, not bigger oir anything
and a local hunter seen it, turned us in, and we got a whole crap of grief and ended up tearing it down, due to we didn't go thru the proper channels??
and it was a simple waking bridge made of pine tree's we dropped off the property! OUR property!

so, again, some times its better to ask first than find out the hard way?

 

[j-bird]

I know in my area it's all a matter of the "classification" of the stream as to what you can and can't do to it. A "seasonal" stream you can essentially do whatever you want.....a perennial stream is an entirely different issue.

Just make sure you realize the power of moving water. I had a culvert "issue" last fall with one that went under the county road, where the metal culvert had rusted thru and water had gotten under it and then all hell broke loose. The entire road was gone for a good 10 foot span!!
The county came in and took 2 or 3 days and fixed it properly but it certainly demonstrated how a small stream and turn into a serious issue under the right situation. I think I posted pics in my property tour thread of this little issue (page 4 if you want to look). Keep in mind this stream is a perennial stream and flows water year round and was maybe 3 feet wide......so it's more than it sounds like you are dealing with, but just a good example of why stream crossings and the design of them can be so important.

I have a county road that is what is called a corduroy road, the foundation is logs like you mention and then simply covered with gravel. They did this in a swampy area so the road "floats" so to speak. Every once in a while when they grade it they catch a log and then it turns into a head and butt scratching session as to how best to fix it. It's about a 1/4 mile section of road that is not well traveled and I am the only full time resident on the mile stretch of that road so I don't see them ever doing much with it. If you didn't know it was constructed like that you would never tell.

 

[Natty Bumppo]

I know in my area it's all a matter of the "classification" of the stream as to what you can and can't do to it. A "seasonal" stream you can essentially do whatever you want.....a perennial stream is an entirely different issue.

Just make sure you realize the power of moving water. I had a culvert "issue" last fall with one that went under the county road, where the metal culvert had rusted thru and water had gotten under it and then all hell broke loose. The entire road was gone for a good 10 foot span!!
The county came in and took 2 or 3 days and fixed it properly but it certainly demonstrated how a small stream and turn into a serious issue under the right situation. I think I posted pics in my property tour thread of this little issue (page 4 if you want to look). Keep in mind this stream is a perennial stream and flows water year round and was maybe 3 feet wide......so it's more than it sounds like you are dealing with, but just a good example of why stream crossings and the design of them can be so important.

I have a county road that is what is called a corduroy road, the foundation is logs like you mention and then simply covered with gravel. They did this in a swampy area so the road "floats" so to speak. Every once in a while when they grade it they catch a log and then it turns into a head and butt scratching session as to how best to fix it. It's about a 1/4 mile section of road that is not well traveled and I am the only full time resident on the mile stretch of that road so I don't see them ever doing much with it. If you didn't know it was constructed like that you would never tell.

You nailed it. My biggest reason for considering a bridge is because of the flow I know I get every spring. If I go the culvert route I am going to need to lay down several pieces side by side to make it wide enough to handle the flow.

I have been calling my log trails corduroy with my family and friends but I wasn't sure if that was the correct term.

Thanks for your thoughts.

 

[alldaysit]

There are some good articles out there from universities on how to cross areas like this for logging. What you would most likely need is a "non-permanent" type. A bridge is permanent. Corduroy is not. I would lay down some non-woven geotextile matting, cover with those 8-10" logs, put some 8" or 4" schedule 40 PVC in there also to assist with draining. You could even cable the logs together to make a "mat".

My tractor weighs about 4000 pounds, and I have a corduroy road we made that goes over a swamp. I found out that using 6" trees is the easiest and most effective. I feel I could drive a Dozer on those 6" trees, but I also have a "bottom" to the swamp.


Sent from my iPhone using Tapatalk

 

[Natty Bumppo]

There are some good articles out there from universities on how to cross areas like this for logging. What you would most likely need is a "non-permanent" type. A bridge is permanent. Corduroy is not. I would lay down some non-woven geotextile matting, cover with those 8-10" logs, put some 8" or 4" schedule 40 PVC in there also to assist with draining. You could even cable the logs together to make a "mat".

My tractor weighs about 4000 pounds, and I have a corduroy road we made that goes over a swamp. I found out that using 6" trees is the easiest and most effective. I feel I could drive a Dozer on those 6" trees, but I also have a "bottom" to the swamp.


Sent from my iPhone using Tapatalk

Thanks Alldaysit. Great ideas. I do like the idea of adding some pipe to help the water flow under the logs.

 

[Redonthehead]

Commonly done in my area are "low water crossings" where the banks are knocked back and rock is placed in the bottom of creek. Then just drive down the ramp and through the water. They can require maintenance over the years due to loss of rock and silt building up in the eddys of the ramps.