Culvert question

[SouthernTier]

Snow's finally melted down at my land.  One project for this year is extending the driveway to where the cabin will be built.

I have to cross an intermittent stream.  It is dry most of the year (in fact it was dry last Sunday and it is still early spring), but of course need to plan for the times when it isn't.

Here's a view of it with as much water as I've ever seen in it; this is this past January when there was a huge mid-winter thaw:



It is just about 3 feet across (those are 2x6's in the photo below) and from the foot bridge to the bottom it is about 2.5' deep.



My dilemma is this:

My understanding of culvert installation is that ideally you need about one foot of fill (e.g. bank run) above the culvert to spread out the weight.  If I got a 2.5' or 3' culvert here, the top of the driveway surface would be well above the current elevation, and make installation difficult. 

I could dig down more I suppose, but I don't know what I'd run into since it is all rock in the creekbed (so actually maybe I couldn't dig down in reality) and then the bottom of the culvert would be well below the current upstream bed elevation.

I was thinking the best way to approach this would be to install two side by side 2' culverts.  However, I am sure there are probably drawbacks to this.  The obvious drawback is that water would try to flow between the culverts and wash out the fill.  But could that be overcome?  For example by filling sand bags with bank run and piling these up around the upstream ends of the culverts?  What about mixing up several bags of concrete and forming that around the culverts, possibly with some sort of wire lath?

Any thoughts on this?

[MountainDon]

A problem with multiple but smaller culverts is that they don't equal the same carrying capacity as the larger, as a rule.

A formed and poured in place steel reinforced concrete box culvert may be a  good alternative. It can be as wide as the ditch and low profile.

[Redoverfarm]

One of the biggest problems installing tandem culverts with minimal diameter is that trash will catch in them and against the middle.  Would a bridge work or something like a poured culvert?  Of couse you would have to "rip-rap" to avoid errosion.  If you go with twin culverts I would pour a diverter in the center and some sort of wing walls to force the water through them independently.  Amazing the force water has especially against soil. 

[SouthernTier]

Thanks for the quick responses.  I knew there would be some drawbacks. 

I don't have to worry about trash build up (limited upstream distance, and there's nothing up there) but if you define "trash" as rocks and twigs, then yes.

Part of the reason water can be so erosive is not just the power of that heavy stuff, but also because things weigh much less when underwater.  Rocks don't float, but it is way easier to pick one up underwater than in air.

I would really like to take advantage the inherent strength of corrugated plastic culverts rather than form and pour a concrete culvert.  in the end, that sounds quite expensive and really needs some engineering.

I'll look into what it would take to form and pour a diverter.

[cholland]

Maybe a 3'-4' culvert, cut in half. So it would be like an arch? A bottom-less culvert. I've seen it done on forest roads usually with steel not plastic. Up to 10-12 feet or more. On streams with fish it's better for fish passage, etc. I would go as big as possible. No matter what you plan for Mother Nature will out do it.

[firefox]

Maybe use the above idea as a form for some reinforced concrete.

[Don_P]

Our soil and water agent sized our culverts based on the drainage, slopes and cover and historic rainfall. They do this as a free service, they want good crossings. He suggested either a single 36 or double 30"... that made the decision pretty easy. For us the creek lay in a general depression as well as the creek cut itself. By starting well back and rebuilding the grade for a good distance either side of the creek it made good crossings.

[GSPDOG]

They will need to know the flow what I did for mine.  Used a double walled culvert (smooth on the inside ribbed on the outside for gripping power)  Used 2" clean gravel over the culvert.  Use 2" clean none of mine has moved even with a 4" rain over an hours period, ran over the top of it but did not move the rock.  I expect that will be the worst case I will ever see.  It also sheeted the water.  In my case I used a 24" culvert 90% of the time this area has no running water.  I would not cut on in half as it will compromise the strength, there are some that are designed specifically for that use.  Mine has had 22,000 lbs. driven over it several times without compromising the culvert.   To prevent erosion on the intake side I place several bags of concrete drove rebar through the bags and let them harden over time.  Then pulled the wrapping off of them later.

http://www.motherearthnews.com/diy/culvert-installation-all-you-need-to-know.aspx#axzz2RrntuVGN

http://hrpoa.org/Culvert%20Information.pdf

[SouthernTier]

I went ahead and pulled the trigger and put in a double culvert this past weekend.

Cutting to the chase:

Before photo (April this year).  The wooden stakes are the edges of where I plan to extend the driveway into where I will build the cabin.



After photo from about the same location.  You can see the same stakes at the lower middle and left (the upper middle ones I had to remove for building).



Did it all by hand.  Way too much work.

Couple of things:

It would be nice to have the diversion structures upgradient, but I have a built in diversion structure on the right with the tree there.  Here is a view before I put in the gravel.  I put in 8 80# bags of concrete mix along the heads of the culverts to armor them.



BTW, as you can see, I put in a 24" and an 18".  As I discussed above, I was thinking two 24" culverts because the natural width of the trench was 48".  The local stores only had the 24" and 18" in stock.  Almost canceled the build until I realized those were inside diameters.  Looking at outside diameters, these two were 48" wide, which is what I needed (still plenty of capacity).

As this picture shows, I have a pretty solid anchor on the right with the tree.  We will see how the left side holds up.  The soil is pretty non-erosive.  That also means it was just about impossible to excavate as well.  Here is a picture of one of the soil piles about half way through:



It was about 30% rock fragments embedded in loam.  To get this out, I had to first break it up with the pick/mattock, then manually throw up the rocks, scrape the soil with a McLoed fire rake which exposed more rocks to hand pick out, and only then could I push a spade into it.  Thankfully it was nice and cool all weekend.

But still, will have to keep an eye on the left side to see if starts eroding.  Also keep "trash" out of getting caught up in the middle.  But shouldn't be too much of that.  Still have some work to do at the lower end where the ends of the culverts are still below the old creek bed.  Will get to that later this summer; not worried as this should stay dry until fall if history is any guide.

Some more pictures:

Looking upstream after about 90% of digging done:



Another 90% shot.  This is two photos stitched together.  The culverts came in 20' lengths, but I cut them down to ~17' because the creek was already starting to bend at that distance.



First (24") pipe in.  I had to manhandle these in and out several times to make sure the walls were straight and the floor level.  I used native soil to build up under the bottoms to provide bedding once I got the floors and walls straight.



Another view of just the first pipe.  That was a lot of soil to dig out (note, two piles, second in back in the shadows is even larger), considering I had to essentially dig it twice - once to break up, and a second time to chuck out of the trench.  Some of the large rocks I dug out are on the right.



Second (18") pipe in.  Tight fit = good.



Overall, would have liked to have a longer more gradual lead in at the upgradient portion, but this is all I had to work with.  The pictures at the top of this topic are the most most water I had ever seen in this creek, and that was only 3" deep and 36" wide, and these culverts at full capacity provide 7 times that much flow (neglecting friction losses due to the pipe walls), so unless I get blockages at the point where they meet, I should be OK.

Will be putting more bank run over the top of the pipes when I put the driveway extension in.

[SouthernTier]

More than a year later, got the driveway in for which I installed the culverts.

This is a plan view of the extension (as planned):



Some before and after pictures (not all from the exact same spot):

Here is where it actually goes over the culvert:

Before:



After:



The Bend into the woods:

Before:



After:



Another view of the bend:

Before:



After:



The bend into the woods looking the other direction.  You can see my shed in the woods (just above the tools) if you squint hard enough:

Before:



After:



It came out really nice.  100 tons of bank run and a very talented machine operator.

Next up, the cabin, which will be at the end of this road (to the right in the last picture pair).  My wife says I may be able to afford starting building next year.  We'll find out.

[Erin]

Looks good!   

[SouthernTier]

I just finished updating my cabin design thread, but I actually have been making incremental progress towards the actual construction.

After getting most of the driveway in last year, it still didn't go all the way to the cabin site.  The guy who did the driveway did a fantastic skilled job, but his tractor wasn't capable of bench cutting the side slope beyond what you see above.  So I spent a couple of days this summer with a pick digging the bench cut.  I moved the topsoil up to the camp fire ring where it needed it, and did a cut and fill with the mineral soil to make a a good 11+ foot wide surface.

I then ordered two 20-ton loads of bank run and borrowed my neighbor's tractor.  It took a while since I'm not that skilled with the machines, but I got it all moved and now the driveway extends to where the cabin will be built.

[Mike 870]

I think your bench cut looks pretty good.  Still a slight pitch to shed water, but not too drastic.

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[garyc]

You're place is looking good, I would like to give you a warning do not have any fires near your plastic culvert pipe. It is highly flammable and it burns like gas and it is difficult to put out. 

[SouthernTier]

Thanks for the warning Gary.  Not much fire danger here in the northeast, but I will make sure I don't burn any brush near it.  Plastic pipe is what is used pretty much universally around here, including what the town put in at the ditch where the driveway hits the road.

Here is a picture of the bench cut before I placed the gravel, showing some trees I dropped to help provide some stability as the gravel set up.  They will rot in time, but by then the gravel and fines should be set up well.