Small creek bridge abutment design?

[Slackdaddy]

I figured I would start a new thread for how to design/build an abutment,, as my other thread was about beam sizing.

So, my creek runs through a bottom that is about 100 yards wide and absolutely flat.

The soil is silty clay,, problem is when I put in a foot bridge 10 years ago, I concreted the post in about 1.5' back from the bank,, but over the years the bank has washed away, exposing the footer.

So, I will be putting my Tractor bridge in upstream about 100 yards,
The 2x4 in the picture is 12 feet long,, and has 1 and 2 foot marks on each end (black lines)
The water is somewhat low for this time of the year, but gets a few inches lower mid/end of summer.
One summer it did dryout,, and most spring/summer it over flows it's banks once or twice, putting a foot or so of water across the whole bottom.

Any Ideas on Abutments? I am very skilled in Masonry and structural concrete.
I was thinking trying to dig down even with the bottom of the stream (even with the top of the bank) and pouring a footer about as high as the water is now,, (this would be easier if the water goes down come late summer.)
Then forming and pouring a abutment wall on the footer.

Other idea was to get some used "sheet Piling" about 4' long and driving it down just below the lowest part of the stream bed, digging out behind it about 2' back, and back filling with concrete and stone.
No mater what, I want the abutment to abutment distance to be no tighter than the top of the stream bank,, I do not want it to be a constriction when the bottom floods.

Any ideas or words of wisdom??

 

[Streetcar]

Can you drill piers below creek level

 

[2manyrocks]

Is there bedrock below the water or just more dirt?

 

[Slackdaddy]

Is there bedrock below the water or just more dirt?

No bedrock, nothing but clay, silt and soil in this area.
You may find a stray rock 2-6" dia on a rare occasion.

 

[Slackdaddy]

Can you drill piers below creek level

Hmm, drilling them would not be a problem.
Depending how close to the creek, they may fill with water.
That "should" not be a problem come late summer.

Hoping to get my abutments (or piers ?) about where the top of the stream bank is,, that is ~8 foot span,, I could easily span that with 5" High I beams, and transporting them would be no problem.

 

[2manyrocks]

No bedrock, nothing but clay, silt and soil in this area.
You may find a stray rock 2-6" dia on a rare occasion.

Our bridge is sitting on the limestone bedrock in our creek. Not really knowing how to make this work on pure dirt, I'm going to shut up and hope someone who actually knows what they are doing will offer some suggestions.

 

[dodge man]

I’ve done construction staking on highway and a couple of railroad bridges. There is a couple of different ways it’s done. The most common way is piles driven down. This are usually steel I beams. Then a concrete abutment or pier is formed on top.

The other method is just a concrete spread footing. It usually ends up pretty large for highway bridge but the one I remember wasn’t that deep. I’m sure it was below frost depth.

Some kind of concrete is probably the only practical way for you unless you have access to some heavy equipment. It should probably be deeper than you are planning but unless you plan on building some kind of coffer dam. On bigger bridges they also have a lot of rebar in them, once again I’m not sure it’s needed for you.

I‘m not sure just a chunk of concrete behind the creek bank won’t work for you and be the simplest. If you have a backhoe it can be deeper than the creek, just dumping concrete in a wet hole won’t hurt anything.

 

[Streetcar]

Hmm, drilling them would not be a problem.
Depending how close to the creek, they may fill with water.
That "should" not be a problem come late summer.

Hoping to get my abutments (or piers ?) about where the top of the stream bank is,, that is ~8 foot span,, I could easily span that with 5" High I beams, and transporting them would be no problem.

Drill hole 12 in or more in diameter . Go below existing creek bottom. One hole at each end of abutment
put rebar in hole, rebar should extend into your abutment
fill hole with concrete, pour abutment on top of piers with rebar in abutment

 

[EddieWalker]

If it was me, I would dig out the footing in the shape of a T. I would want the long part of the T to come back from the creek at least as far as the T is wide, but probably twice that distance would be ideal. Depth would be two feet, but I don't have to deal with freezing temps. If freezing is an issue, maybe drill down with an auger to get extra depth at each end of the T.

For retaining walls, I believe this is called a Deadman.

 

[Streetcar]

You want to be at least a foot back from existing creek bed with your piers. The pedestrian bridge is failing from scour. Having new bridge footing below the creek bed helps protect against scour

 

[Slackdaddy]

Welllll,
A not so good turn of events.
I was talking to an engineer friend about abutments, beam span, etc for my bridge.
He stopped me mid sentence and asked if I had secured permits with the State Environmental agency and/or the corps of engineers ???? Say what??

He said according to the USFW maps, my creek bottom is a potential/likely wetlands.
I said it is dry except the creek, even when I dug post 2' down.
No matter, the state considers it non tidal wetlands UNTIL I hire an engineer to survey it, etc, etc to determine if it is wetlands or not. ~ 3,000.00 to have that done and at least a 50% chance he will determine it wetlands.

If I were to disturb anything down there I would be looking at 20K to undo it.
I asked about the neighbors riding 4 wheelers in the bottom on their property,, he said "recreating" is not something they inforce,, but building a bridge over a stream,, any excavating (digging a hole), filling (concrete),, they will crucify Me.

So much for my bridge

 

[Waterskier]

You didn't say what state you are in but you are right to fear the wetlands permit. Usually your best defense is that you must have the construction to avoid diminishing the value of the property due to not being able to access both sides of your property.

FWIW an abutment and beams is the hard way. Consider a "low water bridge" which means lay a bunch of culvert pipes side by side in the creek, place heavy stone fill in the center and then encase in concrete to form a road over the creek. Keep the level as low as possible so flooding can easily flow over the top of the bridge.

Good Luck!

 

[rogerius]

Why are you not install culverts instead building a bridge?

 

[Slackdaddy]

Why are you not install culverts instead building a bridge?

I am in MD,
I have talked to a few people who deal with situations pertaining to non tidal wetlands,, They ONLY form of creek crossing would be a temp bridge that spans from bank to bank without disturbing the actual creek bed.
A temp bridge would be allowed for forestry and Ag purposes,, "Temporary" is the key word.
I could apply, about $300, they would inspect before, then after I remove the temp bridge.

But a culvert is beyound a big "No" from everyone I have talked to.

 

[Streetcar]

You didn't say what state you are in but you are right to fear the wetlands permit. Usually your best defense is that you must have the construction to avoid diminishing the value of the property due to not being able to access both sides of your property.

FWIW an abutment and beams is the hard way. Consider a "low water bridge" which means lay a bunch of culvert pipes side by side in the creek, place heavy stone fill in the center and then encase in concrete to form a road over the creek. Keep the level as low as possible so flooding can easily flow over the top of the bridge.

Good Luck!

If he worried a bridge over the creek will run into wetland issues, a culvert will not work

 

[dodge man]

If it’s out in the middle of nowhere you might be ok but…………

 

[Jstpssng]

That stinks. Sometimes rules create the very problem which they are supposed to guard against...
Now you will continue to drive through it, creating mud everytime that it rains.

 

[Slackdaddy]

Funny thing is,,,,, When I was talking to the engineer who is well versed in the wetlands issue, I asked about my neighbors who have acreage just down stream of me. They race their 4 wheelers down on there property in the bottom. Through the creek, etc.
He said "they will not touch them, because they are not excavating, filling or building, even though they are destroying the stream, nothing can be done. But if you BUILD a bridge, you will be crucified."

 

[EddieWalker]

Where I grew up in California, a buddy had some land next to a Park. The Park Police and Rangers where always messing with us because his easement allowed us to drive through the Park, but vehicle traffic was off limits to people using the Park. They even landed helicopters to check our ID and make sure we where allowed to drive to his land on his easement. When the road started to erode, the Park arrested his son for fixing it, which lead to a court battle that he won. This happened over and over again. He was a local government employee and he enjoyed fighting with the Park, so these things happened all the time.

The biggest battle was when he "cleaned" up an old pond that was full of trees in a canyon near his cabin. Since the Park was not able to prove that the pond wasn't there before he "cleaned" it up and "rebuilt" the dam, they couldn't do anything about it.

If there was a bridge there previously, say 50 years ago, and it was in need of "repair", couldn't you just "rebuild" the bridge and not violate any of their rules?

 

[2manyrocks]

Wonder if they'd have to inspect and permit this before each use?

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