Lake traffic undercutting retaining wall

[85Hokie]

Guys - Girls,

I got a problem that I need someone with experience on this to lend me a hand.

Back in 2001 I bought some property on a large lake here in VA, gorgeous place, then it was a shoreline.

AT THE TIME the water had receded almost 5 feet!! WHICH was very rare! While this was going on, I constructed a fantastic wall that no owner has on the lake (hard to do when water is there!) - it took me months to do and was a hellva lot of work!

As you see in the pictures, the water when up to full pond comes up about 2/3 of the wall - last picture. 15 years later I have a serious problem!

The same effect that pulls gas through a carburetor is undercutting my wall!!!! AND doing a damn fine job of it!!!!

The water has receded again, about 3 feet - and I can walk in front of the wall, the gravel that was packed with a tamper in 2001 has been undercut by the boats that come around at the end of the cove where I am located, and the wakes come through and run across the face of the wall creating the venturi effect.

I can stick my flat hand under the wall at this time!!!

I am not fear that the wall will collapse - if you look in the pictures you can see the tie back system I used - and there is are 2 pieces of #4 bar hammered down through each of the entire block stacked. SO I feel ok that it will not tumble - but if this keeps up, something bad is gonna happen!

I have raked rock BACK in front - and this might help a bit, but these rock will wash back out........

I can place rip-rap in front, this will help and they will not move, however, it will look like......

I am thinking of actually digging out about a 3" wide trench in front of the wall and using a loose mix of mortar, flowing the mortar BACK under the wall......I have a feeling all that work (100 ft of wall) will not work either!!

I have built a jetty on the incoming side....it seems to help a bit, but the waves stillllll come in and undercut the wall.

Anybody have any thoughts???

thanks in advance

 

[North Idaho Wolfman]

You need to put some typar / Landscape cloth covered in rock.
It will keep the sand / dirt from washing out.

 

[Mike.O]

How many feet or inches is the base of your wall below bottom of lake ELEV.?

 

[William1]

I'm no expert but, I strongly suspect it is the footing. At some point the wall will dip and the the tie back you have will loosen and the wall will not longer be straight.
I did a creek that fills my lake ten years ago. I did a rebar'd 2' deep by 18" wide concrete foundation.I put perf drain pipe behind it as well as fabric and gravel. I have had a few massive rains and everything has stayed in place.

 

[85Hokie]

How many feet or inches is the base of your wall below bottom of lake ELEV.?

When the lake is at normal pond....there is about 18" of water above the footer.

The footer consisted of 6" of 57 and crush-n-run that was tamped with a jumping jack tamper.

NIW - the cloth was laid on the shore side......hard to place a cloth on the water side at the footer level

 

[Mike.O]

When the lake is at normal pond....there is about 18" of water above the footer.

The footer consisted of 6" of 57 and crush-n-run that was tamped with a jumping jack tamper.

NIW - the cloth was laid on the shore side......hard to place a cloth on the water side at the footer level

The main factor isn't water above the footer, it's how deep the bottom of your first block is below the bottom of the lake bottom soil. If the bottom of your first block was set at the same elevation of the dried up lakebed then the movement of the water will wash away below the wall in time. If it was set 8+" below grade then the bottom of the wall would be in equilibrium and would be stabil.

If this is the case then I believe your "flowfill" option would be the best. You could get a 5000psi mortsr mix and mix it loosely. If you can get it under the wall then you could prevent more washout, As long as you bury the mortar so that doesn't undermine. This mortar would essentially increase the overall depth of your wall

Just my thoughts. Also a decorative riprap at the base after you stabilize the wall would break the wave action beating on the base of your wall and surely help

 

[85Hokie]

The main factor isn't water above the footer, it's how deep the bottom of your first block is below the bottom of the lake bottom soil. If the bottom of your first block was set at the same elevation of the dried up lakebed then the movement of the water will wash away below the wall in time. If it was set 8+" below grade then the bottom of the wall would be in equilibrium and would be stabil.

If this is the case then I believe your "flowfill" option would be the best. You could get a 5000psi mortsr mix and mix it loosely. If you can get it under the wall then you could prevent more washout, As long as you bury the mortar so that doesn't undermine. This mortar would essentially increase the overall depth of your wall

Just my thoughts. Also a decorative riprap at the base after you stabilize the wall would break the wave action beating on the base of your wall and surely help

Mike,

you are correct - the tamped 57, crush-n-run was set below what was grade.
So basically the top of the crush-n-run was "zero" grade. And the blocks placed on top of the gravel bed.

The water is very rare to be near or below the wall.

Over the years, the waves come "crashing" in - like a roll after roll - all the while the water is being forced against the wall at about a 45 degree angle. The bernoulli effect is what is happening -
https://en.wikipedia.org/wiki/Bernoulli's_principle

the water rushing by at an increased speed, creates a low pressure at the base of the wall, and the low must then allows the small rock to be pulled away. Much like someone smoking in a car with the window cracked, speed increase outside the car, low pressure on outside,higher pressure on inside - smoke rolls out.

I will need to dig down to a point that will allow the water to pass but not allow the undersilt to be pulled away.

And yes - I may still have to place something there to break up the pressured effect.

 

[Mike.O]

Mike,

you are correct - the tamped 57, crush-n-run was set below what was grade.
So basically the top of the crush-n-run was "zero" grade. And the blocks placed on top of the gravel bed.

The water is very rare to be near or below the wall.

Over the years, the waves come "crashing" in - like a roll after roll - all the while the water is being forced against the wall at about a 45 degree angle. The bernoulli effect is what is happening -
https://en.wikipedia.org/wiki/Bernoulli's_principle

the water rushing by at an increased speed, creates a low pressure at the base of the wall, and the low must then allows the small rock to be pulled away. Much like someone smoking in a car with the window cracked, speed increase outside the car, low pressure on outside,higher pressure on inside - smoke rolls out.

I will need to dig down to a point that will allow the water to pass but not allow the undersilt to be pulled away.

And yes - I may still have to place something there to break up the pressured effect.

Yes i fully understand the Bernoulli principle (civil engineer). Took numerous fluid dynamic courses back in the day.

So you know whats causing it, so I would stabilize the wall, via flowfill, and get material in front of the wall. That way the action of the water removes the excess material not the material below your wall. There's no altering physics, so let the waves move the excess material away, not your base material.

Sounds like you have a pretty good understanding of whats going on. Good luck! And what a nice piece of property you got yourself there!

 

[coachgeo]

Can you drive in some post in the water in a line that is at a angle from the wall and string in a used Trampoline bed across them. Water can go thru it..... but it slows the wake way down... probably stops it. no more Bernoulli effect. You will need to replace bed occasionally but I bet you can find free ones..... an upholstery shop can repair/modify them too.

 

[skeets]

I know its not pretty but how about a couple loads of big rip rap dumped along the wall I would think that would defuse most of the wake into little movements instead of big ones,, but what do I know

 

[D2Cat]

I k now its not pretty but how about a couple loads of big rip rap dumped along the wall I would think that would defuse most of the wake into little movements instead of big ones,, but what do I know

Pretty much what post #2 said. Make sense to me, just like on the face of a Corp of Eng. dam.

 

[niteshiftfromkc]

I have a creek that goes through the front of my property. It was eroding away under the foundation of the bridge for our driveway. I had to bring in a bunch of fill dirt to bring the level up and tamp in the dirt under the foundation. I then installed a geofabric over the dirt. I can't remember the actual product name, but it is a heavy duty fabric (looks like felt) that comes in 12' wide rolls. I would say it is approximately 1/16" to 3/32" thick. I got it from our local USDA outreach office. They were selling it to farmers to use as an underlayment for gravel driveways. This fabric then got covered up with 6-8" size rip rap.

This fabric/rip rap combination has really stabilized that area from some of the drenching floods that we get. I haven't had any undercutting of the bridge foundation in the 6 or so years since I put it in. The only problem that I have is when the creek gets to full capacity it moves some of the rip rap around and uncovers the fabric. After it goes down I have to go move the rocks back into place.

As far as your wall, if I am reading the post correctly, you do not have any of the blocks below the lake bed? On the retaining wall that I installed, I had 16" of block below grade. If memory serves, the manufacturer said to have 1" per every foot of wall, with a minimum of 6" below grade. I had to have mine engineered due to the height and the soil testing, so my engineer had it two courses below finished grade with a 8" AB3 footing that was tamped into place.

My suggestion would be to fill in the undercut areas, then use the geofabric and the rip rap. You might consider adding in some fill dirt on the lake side to go up a few inches on the bottom course prior to putting in the fabric. Do a search for geofabric online that people use for pond liners. That geofabric will help with the eroding and the rip rap will help keep the fabric in place. If you don't like the look of the rip rap, you might consider large river rock. That is pretty pricey though.

 

[skeets]

Pretty much what post #2 said. Make sense to me, just like on the face of a Corp of Eng. dam.

I though it sounded familiar

 

[Tooljunkie]

Geotextile or filter cloth. A bag of sorts, geo on base, a layer of rock then geo rolled over and more rock to cover the geo. the filter cloth will keep the silt from washing out. There a few types,one is a woven type, tough for under roads, the other is a mat, that is thicker and filters better, used around culverts to prevent washout. My best friend is the local drainage authority,has designed some drainage solutions where others have failed.