Want Advice - Interesting Challenge

[BigEddy]

A previous Boss, now retired wants me to help him with a project.
He has a 60' seawall 4' high that is tipping into the lake. Wants me to help him straighten it up and reinforce it so it won't collapse.
Wall is poured concrete, 60' long, 4' high, about 14" wide at base, 10" at the top, on a wider footing. Saw cuts every 10'. With time and waves, the footing is breaking down, and the pressure of the dirt is pushing it out. Probably tipped forward about 12" at the middle.

Here's the plan.
Dig a series of holes parallel to the wall about 8' uphill, 4'long, 16" wide about 3' deep, add some rebar for strength, with an anchor loop, and pour concrete deadmen about 4x2x16". Dig a narrow trench forward to the seawall from the centre of each deadman.

Then excavate all the dirt next to the wall all the way along it 2' +/- wide, down the 4' until the wall is essentially freestanding.

Drill through the wall about 8" below the top and put some 6"x6" plates on the water side with a large anchor bolt through the middle, then attach a cable from the anchors to the deadmen. Probably a cable every 6-8' or so. (My ex-boss suggested 8' long solid rods instead of cable - don't know which would be better) Cable would be essentially level, starting 8" below the top of the wall, ending at the middle of the deadman about 24"" below ground uphill.

Tension the cables using the bolts projecting to the water side, then backfill with good gravel and sand for drainage. Finish with 6" topsoil. Goal is to stop the wall going any further first, then pull it back in line if we can.

Here are the questions.
Am I missing anything here?
Anybody else done something like this?
How long would you think this might take us? Looks like good soil to dig in, no major rock, but I can't tell for sure.
Cables versus solid rods?
Are we likely to be able to pull the freestanding wall back vertical with ~10 cables being torqued down via 1" bolts or would you use a series of come-alongs first?
He wants to pay me - how much? We're on good terms, but he's never done anything for me and don't expect he will in future. He'll help out all along, and provide all the materials and beer. I have the equipment and the brawn.

Any advice appreciated!

 

[Knute]

Sounds like a very big project. I'm not an engineer, but this solution sounds like treating the symptom - the wall tiping out - and not the problem - why is the wall tipping out. Won't the ground beneath the wall continue to erode until it collapses?

I don't know how you would do it, or if it's possible, but wouldn't it be better to fix the ground being eroded under the water side of the wall?

John

 

[BigEddy]

Actually that's part of his plan too, but the post was getting long.
Step one, straighten it up and hold it back.
Step 2, improve and reinforce the footings on the lake side. Can't do that until the water drops late in the fall. I'm not doing that job.

 

[WVBill]

How to deal with corrosion on the cable/rod, plates, anchor bolt. They're going to be in there for a real long time. Is galvanized enough protection? I don't know.

 

[Glenn9643]

"Wall is poured concrete, 60' long, 4' high, about 14" wide at base, 10" at the top" ... "Probably tipped forward about 12" at the middle."
10" thick at the top, with a 12" tip at the greatest point; you'll need a lot of thread on your bolt to pull it straight. 13" long just to get through the wall and attach a nut to front and cable in back. Then if you're going to pull the wall 12" to remove the tip, the bolt must extend that far behind the wall before it attaches to the cable, because the bolt must slide through the hole in the wall as you tighten. If you attach to cable, what's to keep the bolt from turning as you try to tighten? It seems to me that if you use cable, as you get the wall straightened, you can gradually take up cable and let out on your bolts to help lessen the length of thread required. I've seen galvanized allthread rod at a lot of places in varying lengths (4-8') that you could probably use to fabricate bolts with loop on one end for attaching the cable, but don't know how much load it would stand compared to a good "bolt". Make the loop large enough to insert a section of pipe or steel bar to keep the bolt from turning. ??? Good luck.

 

[DavidJ]

That sounds like a solid plan. We have done that several times in the past. As for tension units I would use long large turnbuckles and it really won't matter whether you use cable or rod. If you get long enough turnbuckles and place them in the trenches you can take them up to straighten the wall. Galvanized metal parts should be good to use just be sure to coat any nicks or exposed areas with the spray galvanize before covering them up.

 

[MossRoad]

<font color="blue">Then excavate all the dirt next to the wall all the way along it 2' +/- wide, down the 4' until the wall is essentially freestanding. </font>

Sounds like an interesting project. /forums/images/graemlins/laugh.gif

How far down below the water level does the wall extend? If you get the wall freestanding won't the water pressure have a tendancy to push it into the hole you just dug? Might be cheaper to have sheet steel seawall driven in by a professional company in front of the existing wall, then filling in the space between the steel wall and the existing concrete wall.

Either way, get insurance before helping a friend with this type of project. Especially if you are doing it for money. Also check codes, environmental issues, permits, etc... anything around bodies of water these days could become a legal quagmire. While it sounds like a great project, make sure to cover your assets first. Good luck and keep us posted as to how it turns out... and take pictures before, during and after.

 

[Currmudgeon]

That sounds like a reasonable approach, although it might be simpler to demo and repour the wall. Your way sounds more "interesting," though.

A gravity wall is typically 2/3 to 1/2 as thick as it is high. Walls are seldom constructed that way, as they are expensive. This explains why so many walls are falling down. Tension rods and deadman anchors is a convenient, although labor intensive, way to support the wall against the overturning force of the earth behind it.

I'd backfill behind the wall with drain stone and core some drain holes in the face of the wall. The less water you trap behind the wall, the better off you'll be.

If there is an erosion problem at the toe of the wall, then you're in for more work, particularly if the toe has been undercut. In that case, I think I'd want to pull out the wall and rebuild it rather than mucking with it. Driven sheet piles come to mind as a replacement. You can get plastic piles that aren't too ugly. (nor are they too cheap)

If the toe isn't undercut too badly, you may be able to armor it with stone or broken concrete riprap. It has to be installed correctly, or it tends to sink into the surrounding dirt.

You may need a permit from the Corpse of Engineers or your state Division of Water Resources or whatever they call it in your neck of the woods. Lakeshores are regulated in many areas, although permission to do repairs is often easy or automatically granted. Obviously, the time to find this out is before the regulators show up on site with their red tags.

I hate working for friends. I've had a couple of friendships nearly go sour over that. Payment makes it worse. If you want to accept payment, bill yourself out at whatever rate is customary for that kind of construction in your area. Or work for beer.