Engineering help needed

[Jogeephus]

I have a sea wall that needs fixing and I'm wondering if anyone has ever had to do this type work and am hoping someone might have an idea on a quick easy fix.

Wall stands about 3 foot off the beach floor. At times, water level reaches about 2 foot up the wall. Due to wave action during rough weather waves crash over the top of the wall. Problem I have is the water has created a funnel and by washing the dirt out of the land side of the wall and down the back of the wall and has undermined the footing. The quick fix in the past has been to fill this funnel back with dirt and pack. But after 2 - 4 years it washes out again. I'm wanting to fix it right this time to prevent some major repair work in the future.

My idea: Dig out the funnel area and place some 4 or 6" pvc pipe down in the hole and elbow it at the bottom and run a drain pipe out under the base of the sea wall to allow the water an easy escape route. Kinda like a drain. Was even thinking of putting a cap on this pipe with a bunch of holes drilled in it to make it like a screen. This way - I was thinking - I could place the top of the drain line just beneath the sod. Any ideas?

 

[HerefordSire]

If the temperature of the earth increases one degree due to normal temperature cycles, how much land will you lose?

 

[alabama]

Please post some pictures that include the ends of the wall. Some from a distance that show how the land around you lays. Then include some details. PM me so I am sure to look.

 

[skyline]

How about filling in the eroded areas behind the wall with concrete to stabilize it?

 

[skyline]

Another idea. Put a drain behind the wall with a concrete swale over the top of it. The way I do my wall drains is to dig out as deep as you can without the wall falling over backwards on you. Make the trench behind the wall about 2 feet wide. Lay in a porous geotextile fabric that is wide enough to cover the bottom and run up the sides and then lay over the top completely encapsulating the rock and the perforated pipe. Put about a 2 or 3" layer of gravel in the bottom of the trench and then lay your perforated pipe on that bedding. Once the pipe is installed and laid on a grade to drain freely out the end, finish installing gravel to within about 9" of the surface. Fold the fabric over the top of the gravel completely encapsulating the gravel. At that point, I would put a concrete swale down the length of the wall to divert surface water around the wall instead of allowing it to run over the top of the wall.

The purpose of the fabric is to keep your gravel and pipe from getting silted up. Make sure it's a porous geofabric. The non-porous ones would defeat the purpose.

Let me know if that's a clear as mud and I'll try to clear it up.

 

[backhoeboogie]

After chopping limestone into bricklike blockss, the left over ends and tails are sold as rip rap. A whole lot of folks buy the rip rap who are in your situation. I have sold several hundred tons of it to folks who live on the lakes and boat wakes beat over their walls.

Long term, the foundation is going to erode underneath your wall. The funnels you speak of are exactly what does it. You must have a heck of a good chain wall already. I would put rip rap in the water against the wall first thing. Go a minimum of 2 feet out and 2 feet up. Then I would back fill the holes with concrete if possible. Pack the ground really well. Then run a wide sidewalk on top of the wall. Pour a chain wall and build another wall to back fill in on the opposite side of the sidewalk. Find you some type of deep rooted shrubs that will grow in that situation and plant them thick on the upside of the new wall.

That is the only recipe I know that works for certain long term.

 

[Jogeephus]

Thanks everybody. Skyline, your description is as clear as mud. I see what you are talking about. My wall is long and joins into other walls. There is just one place that I keep having trouble with. Its in a corner where the angle changes. I'm wondering whether or not a drain would allow the overflow of water to drain out a pipe rather than through the soil and under the wall. They let down the lake every other year so I can do some work on it now. I'd prefer not to use rip rap if at all possible and I'd rather not put in as long of a ditch as what skyline was describing since the problem area is only about 3 foot wide. What if I did something like what skyline is describing but limit it to maybe twice the distance of the problem area? Also, should I run the drainage under the wall or just cut out a hole in the wall about a foot beneath ground level? (Please understand I'm taking everything in but am only asking questions.) I'll try and make a sketch of it and post it for better reference.

 

[Angus Cowman]

Jo you could dig it up on the backside like was said and put in your drain pipe going thru the wall and back fill with the rock and material around your stand pipe we used to do this in detetion areas we would take schd 40 pipe and drill 1" hole in it so the water drains into the pipe in a slow fashon and eleminates erosion

 

[Toby L.]

Why can't you drill a few 1/2 inch holes at a 45 dagree angle at your sod line, maybe put a screen over the holes if you have to much dirt running back through.

 

[skyline]

Jogee if the area is only 3 feet wide, I would cut out a hole about 8 feet long centered on the problem area. About 2' wide away from the wall. Use the geofabric on the bottom, sides and top of the hole as described above, put about 3 pipes from the gravel through the wall - spaced evenly, the pipes should penetrate the fabric and go into the bottom of the gravel area and the pipes should be small enough to keep the rock from going through the pipes. Again cover the top of the gravel with the fabric. And I would consider capping the whole thing with concrete as described above, but slope the concrete to allow the water to flow over the concrete over the top of the wall in this instance. You're trying to keep the water from getting in behind the wall and if it does, you're trying to give it someplace to go without taking dirt with it.

I'd use bigger rock in this case, maybe 4" rocks and then you can use 2" pipes. Wanna make sure the end of the pipes are not plugged with rock before you completely fill with rock.

(Imagine a long disclaimer here....)

 

[Jogeephus]

Thanks for all the replies. It has given me enough information to create Plan B. Plan A was based on complete ignorance and I hate to admit would have problably been more work this year as well as year's to come.

(Imagine a long disclaimer here....)

:lol2: :lol2: No need for that. Heck by the time I put my engineering prowess to work I'll probably end up with a dang bluebird house there rather than anything you described.

 

[skyline]

Just joshing ya Jogee. Hope it turns out well.

 

[novatech]

Sand when wet will flow. So any drainage will only cause the sand to flow to that spot. The wall acts as a dam. The only place for the water to escape is under the wall. Path of least resistance will cause it to erode in a particular spot. The funneling you see is the result of the undermining.
Solution ; Cover the surface as to not let the water behind the dam. Definitely go back as far as the wave action. The further back you cover it the longer it will last. What you cover it with depends on your budget. Removal of some of the sand a replacing it with about a foot of clay, maybe add some bentonite, would be the least expensive. Cover with gravel to prevent errosion of the clay.
Even if you stop the wave water you still must contend with rain water.
Weep holes in the bottom of the wall would be good but filter cloth, finer than the sand grain, would have to be installed on the back side. There are special pipes sold for this purpose which can be used. With out the weep holes a tremendous amount of hydraulic pressure can build behind the wall and result in the same problem you now have. Weep holes alone will not carry enough volume to relieve the pressure.
About 5 years ago I did a project similar to this. There was a sand hill sloping toward a house. Over time the water eroded a tunnel from front to the rear of the house . The solution mentioned above has cured the problem thus far.

 

[Aaron]

Have some 12-16 inch rock hauled in, and dumped in front of the wall on the beach. You need something the break the wave action or the erosion with continue. :cowboy:

 

[Jogeephus]

Have some 12-16 inch rock hauled in, and dumped in front of the wall on the beach. You need something the break the wave action or the erosion with continue. :cowboy:

I've done this before on another piece of property and it works good but it also provides the cotton mouths with a nesting area so I don't want to do that here. Too many children at play. The erosion is isolated to this one spot. A lot of the information is making sense as the fella I bought the place from filled it in with sand rather than clay the last time it washed out. I'm going to try this quick fix first.

Anyone got any suggestions on the easiest way to drill a 2" hole through a foot of concrete?

Also, would silt fencing work for the fabric? I can get this free as a friend of mine had to install some on the top of hill because the EPD engineer didn't want the dirt from the construction he was doing at the bottom of the hill to wash up the hill and get into the stream that was about 2 miles uphill from the construction site. :roll:

 

[skyline]

Jogee, the silt fence should work fine. Especially if it's free. I'd overlap it about 6" or so when you have a seam.

Regarding the pipe through the wall, testing labs use these types of drills to remove concrete cores from walls. If you have a materials testing lab nearby, you could call them and ask them what they use to remove their cores from vertical walls. (It's a lot easier when you form the pipe in the wall during construction!)

 

[Angus Cowman]

Jo in your case a Hammer drill should work if ya don't have one big enuff I bet some const equip rental store does or a good sized concrete contractor if ya know one might rent ya one

Have even took and drilled several smaller holes slightly larger than your pipe in a circle and the knock the center out with a hammer
good luck

 

[novatech]

Have some 12-16 inch rock hauled in, and dumped in front of the wall on the beach. You need something the break the wave action or the erosion with continue. :cowboy:

I've done this before on another piece of property and it works good but it also provides the cotton mouths with a nesting area so I don't want to do that here. Too many children at play. The erosion is isolated to this one spot. A lot of the information is making sense as the fella I bought the place from filled it in with sand rather than clay the last time it washed out. I'm going to try this quick fix first.

Anyone got any suggestions on the easiest way to drill a 2" hole through a foot of concrete?

Also, would silt fencing work for the fabric? I can get this free as a friend of mine had to install some on the top of hill because the EPD engineer didn't want the dirt from the construction he was doing at the bottom of the hill to wash up the hill and get into the stream that was about 2 miles uphill from the construction site. :roll:

There is absolutely nothing that will work unless you stop the water from getting to the bottom. The volume of water from waves is simply to great for 2" weep holes to take care of. Secondly with just 2" surface area of filter cloth over a hole this would plug up quickly thus resulting in the same problem. You must get rid of the majority of the water before it travels to the bottom. The weep holes are a secondary drain only. The top can be covered with clay, rubber pond liner, rubber roofing material, asphalt , concrete, or what ever. Anything decorative may be place over it. I would suggest something heavy enough so the kids cannot pick it up. Concrete pavers, boulders, etc. Something removable so that the filter cloth can be serviced if ever necessary. The filter cloth will have to be cleaned or replace over time. The less water allowed getting to it the longer it will last.
A 2" hole can be bored through the wall with a hammer drill. Anything much larger takes a coring drill.
I would also suggest the use of pipe made for the purpose being installed behind the wall. The more surface area of filter cloth the less likely it is to plug. The pipe is cheap and already covered with cloth. Check with Irrigation supply co.'s, Home Depot, Lowes. The pipe can be reduced down to the weep hole being used.
You mentioned that you had this problem in only one spot. Sorry but if you only correct the problem in that spot the water will only travel to another spot to get out. The water picked that particular spot as it was the path of least resistance.
Bite the bullet, do it right. If your like me you probably need the exercise anyway. :lol:

 

[backhoeboogie]

If you drop kickers onto the bottom, sort of like the taper you see on highway bollards, you may save that wall.

I fear you are going to have the soil underneath it erode away within a dozen years or so.

There are busted walls all over Lake Granbury. It is a lot of expense to rip one out and put a new one back.

 

[skyline]

Nova - I agree that the fabric will plug up if you cover the end with fabric. For that reason, I suggest penetrating the fabric (that lines the trench bottom, sides, and top) with the 2" pipes.

Similarly, I don't like to wrap the perforated pipe with fabic, because of a concern that the holes in the pipe will plug up. I try to filter out the dirt before it gets into the gravel trench.

I agree that you can use a non-porous material like clay over the trench instead of the concrete and that this method would provide easier access in the future. The key is to try to get the water over the top of the wall instead of letting it go down behind the wall.