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Critique my Retaining Wall Idea

Grnd93

Grnd93

The Dude
Joined
May 19, 2020
Member Number
236
Messages
738
Loc
Michigan
Our family's summer cottage sits on a hill. To the west, it slopes down to the lake, on the north (roughly 100') and east (20'-30') it slopes down to a swamp (approximately 20' elevation change, not very steep for the most part.

The side going down to the lake is not of immediate concern, but we have been battling erosion on the side and it's now to the point that I absolutely have to do something about it.

My current plan is to find where our property line is and sink a steel beam every 10' to square off the north and east side. I will bolt a course of 12" x 10' channels around the perimeter at the same elevation that the cottage sits at. If I need to add a second or third course that shouldn't be a big deal. Then backfill to level everything out.

i can get steel for cheap and keeping everything 10' or shorter will make getting materials to site much easier.

I'll get photos of the area this weekend. But what are your initial thoughts?
 
initial thoughts are that steel is expensive, but if you can get it cheap, it should work out well. how tall will the wall end up being? drainage is among the most important parts, probably more important than materials even, so make sure you have a way to keep the water flowing away from the wall how you'd like it to
 
It sounds like you are doing a DIY sheet pile. Most places have a requirement for a stamped engineered design for retaining walls over 4-6 ft. Even if yours doesn't, I would plan on being off the property line at least as far as you plan to be tall unless you do get an engineer to take that liability. The key to sheet piles is depth of embedment and that is determined by soil properties and load.
 
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I hope to not have to sink the beams more than 10’. I think that will work everywhere except the northeast corner. Kinda depends where the property boundaries are.

Part of my plan is to maximize useable space. If thr property line falls past the top of the hill i will still build to that line and fill as needed.

This will be done in sections as well, starting at the north west, going along the east side, then the south. Eventually want to do the west also, but that is under a deck so it will be a lot more work.
 
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Kinda the same concept.

Our cottage is very close to the property line (or where i believe it is). So building the wall on the line is my only real option.

I have no intentions of pulling any kind of permits and there is little chance that anyone would rat me out.
 
Knowing how high you think the wall will be is important to gauging your plan. however, first thoughts are the steel spacing is probably too much and is definitely too much for 2x lumber to hold back soil more than about a foot high. The steel will last awhile but the 2x lumber will be a maintenance headache after the first 2-3 years. You need to look at a gravel layer behind the wall for drainage and explore how geofabrics or even landscape fabric will keep the soil from being washed out between the boards. If the wall is short enough, the plans could be modified to work. If you are thinking this will be 5 feet tall or something, scrap the idea and start over.

Edit: I missed the channels in the OP. Ignore the 2x lumber comments.
 
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How you planning on driving the piles? If I was going to hillbilly something like this up I'd do locking ecoblocks with a drain at the bottom and a foot or so of washed pea gravel (AASHTO #8) between the native and the ecoblocks.

I'd also see how cheap I could get a set of stamped plans for it. There's way more to this than you're thinking. But go ahead and take lots of pictures for us! :flipoff2:
 
RusM said:
How you planning on driving the piles? If I was going to hillbilly something like this up I'd do locking ecoblocks with a drain at the bottom and a foot or so of washed pea gravel (AASHTO #8) between the native and the ecoblocks.

I'd also see how cheap I could get a set of stamped plans for it. There's way more to this than you're thinking. But go ahead and take lots of pictures for us! :flipoff2:
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Initial thought is to auger a hole, set the pile and partially fill with concrete, gravel/dirt for the rest. Kinda depends how deep I need to go. There are a couple spots that I will probably have to figure out a way to do by hand.

I guarantee there are probably about 100 details I am missing.
 
On a fill site, segmental block with geogrid is the most economical. If you're getting steel on the cheap and it's decent ground, figure an embedment to wall height ratio of 1.2 :1 ( 8' tall wall needs about 10' buried). Poor conditions or rock effect that ratio. An 8' tall wall with piles 8' on center would probably be HP10x42# or equivalent. Drainage is key, hydrostatic pressure is a bitch.

Disclaimer: I'm not an engineer, just what I do to eat.
 
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Chzbrgr said:
On a fill site, segmental block with geogrid is the most economical. If you're getting steel on the cheap and it's decent ground, figure an embedment to wall height ratio of 1.2 :1 ( 8' tall wall needs about 10' buried). Poor conditions or rock effect that ratio. An 8' tall wall with piles 8' on center would probably be HP10x42# or equivalent. Drainage is key, hydrostatic pressure is a bitch.

Disclaimer: I'm not an engineer, just what I do to eat.
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Good information. Thank you
 
How tall will the wall be if your only using 10' stock? I would say your idea would work up to about 3' , 7' in and 3' out and I think I would put them about 5' apart instead of the 10' you want.
 
dave_dj1 said:
How tall will the wall be if your only using 10' stock? I would say your idea would work up to about 3' , 7' in and 3' out and I think I would put them about 5' apart instead of the 10' you want.
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3’ would probably be good for just about everything except maybe the East side.

i can do 5’ spacing if need be.
 
Grnd93 said:
Considering galvanizing for $.30/lb

our seawall was done with plain steel beams and 20+ years later nothing has rotted away.
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Might be Cor-Ten or similar weathering steel if it hasn't turned into pure rust in 20+ years.

I'd bet it's not good-ol' A36 steel.
 
Grnd93 said:
But what are your initial thoughts?
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:usa:

i0vDj5j.jpg
 
ExWrench said:
Might be Cor-Ten or similar weathering steel if it hasn't turned into pure rust in 20+ years.

I'd bet it's not good-ol' A36 steel.
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Maybe, I was out of state when it was put in.

i can get whatever I use hot dipped cheap enough, so that’s likely the route I’ll take.
 
Chzbrgr said:
On a fill site, segmental block with geogrid is the most economical. If you're getting steel on the cheap and it's decent ground, figure an embedment to wall height ratio of 1.2 :1 ( 8' tall wall needs about 10' buried). Poor conditions or rock effect that ratio. An 8' tall wall with piles 8' on center would probably be HP10x42# or equivalent. Drainage is key, hydrostatic pressure is a bitch.

Disclaimer: I'm not an engineer, just what I do to eat.
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Yeppers. Neighbor built a fucking nice retaining wall next to a canal. Fucking first heavy Floridia rain and all his material was in the canal. Resulted in huge miserable mess to clean up. Fish & Game tore him up big time when they noticed the material was "Pressure Treated" . :smokin:
 
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