I'm sure I can already guess most of the responses so I'll read those just for the entertainment - what I really seek is serious options as to how to address this with the neighbor.

Cliff's Notes before reading everything below: neighbor didn't build a good wall to support our yard (he built it out of wood!) and thinks it's my fault that we put dirt back behind it that it's failing.  

Guy next door is pushing 80.  They cleared the lot to build their home just before we closed on our house 16 years ago.  Old homeowner that we bought from evidently sent the neighbor a cease and desist letter since they excavated into what would be our property by about 5-8' while grading their lot for their footings.  The change in lot elevation is approximately 4'.  Our yard is the higher one and as they built their home, they also built a 4' tall, 55' long concrete cinder block retaining wall without any weep holes for water.  We're in North Alabama so we have A LOT of water to deal with.  Anyway, that block wall fell over about 4 years ago since it wasn't built properly (no gravel below or behind it and no weep holes) and the neighbor decided to replace it with wood!  Yes, you read that right, wood.  He left the bottom row of block in place, dropped some landscaping timbers down in the block holes, filled the holes with concrete, then connected the vertical pieces of landscape timbers with some 2 x 8s and 2 x 10s and called it "good".  We've prepped our yard for a shop and my earthwork guy pushed some of that fine Alabama red clay over to the "fence/wall" to get it all level again.  As you guessed it, the thing is now falling over again.  Now, the crappy part: the neighbor feels this is all somehow my fault that we pushed dirt back in behind it and it's all on me to fix it.  The wall/fence contraption is 100% on his property.  Nobody that I've talked to including my concrete guy will touch it.  My shop foundation is about 12' from the property line and shouldn't be effected when the fence falls.  I'm trying to decide what to do.  I don't like getting into it with a neighbor that otherwise is one of our better neighbors relatively speaking but this really doesn't seem like it's my responsibility at all.

I looked at having my earthwork guy dig out behind it with a mini-ex and then we straighten the fence with the mini-ex bucket.  Then backfill with washed gravel, then a layer of geo-fence tying it into the wall and our yard then more gravel.  Total I'd be about $2,000 into the gigantic band-aid that isn't even my responsibility.  Neighbor has since said in a text message to me: "After looking at the wall this morning just work with your wall, earthwork man and get it upright and I will be happy - you make the call as to how you want to correct the problem. Thanks"  Based on that, he thinks this is totally on me.  What the heck?  Am I out of line here or is he?  

Evidently, to post pictures, I'm gonna need to upgrade my account or host pics elsewhere?  

Ignore him.

Send him a cease and desist/no contact letter.

Just have your dozer guy push his wall all the way over and tell him “do something about it”
Then fuck his truck,kick his wife and steal his dog.

His wall, his problem

I had a shit neighbor in NC.  I sold my house and  moved to MT.  YMMV

Old people like him are impossible to please.

Ignore him.

I should add, my biggest concern is *when* this thing fails, I don't want it to impact my foundation in any way to this shop.
It's gonna be north of $20K in concrete alone and if that back side starts cracking I'm gonna be PISSED.  
Standing at a bit of a distance from it, I can kinda eyeball what would slump away with the fence when it fails and if it goes at about a 45 degree angle, it would still be approximately 6-7 feet from my foundation.
My concrete guy has looked at it and isn't really concerned but I still am, to a degree.

Attached File

Maybe you need a ditch on that side of the yard.

I think you forgot "piss on his leg to establish dominance."

For that, I give your response a 9/10.

dont call him a pussy or faggot while shoveling snow outside with your wife...

Put a toilet on the property line

Can you just do a retaining wall adjacent to your shop to protect your foundation and let the rest go?

Spend the 2k on a fence on your property.

His property, his fence, his problem.

I've considered grading it between the wall and the foundation into the middle with a french drain, lining the surface with plastic, then backfilling on top only with washed gravel.
First issue with that is I'm afraid to get any equipment in there that has any decent weight as all of it is so compromised with that failing (fence) wall.
Second issue, my investment of all of that above would be lost when it fails anyway (or at least half of it) and he obviously wouldn't do shit to put it back I don't think.

Water is definitely the biggest issue here though.  If we just grade the top with something small like a dingo and create some runoff through a slight ditch,  maybe that'll at least "help" and not be too much of an investment on my part.

Honesty I would just offer to split the $2K with the guy to get it fixed right and eliminate potential future problems with your building and move on. It’s not worth the worry or the hassle to fight with the guy.

So I understand correctly.

Your dude pushing the soil basically made the piece of shit fall over? Understanding that it probably would have fell over on its own sooner than later.

You're in Alabama.

It's SUPPOSED to collapse.

What if the wife and dog are old like him? You read OP says he's pushing 80, right? Unless old man pulled an Anna Nicole Smith.

I could but don't really have that in the budget.  I've already built one, the correct way, to hold back my other neighbors yard and actual fence.  Their lot is higher than ours and I did it 100% correctly.  It was a $10k investment on my part.  That wall should be here in 100 years, no joke.

It’s kind of where I’m at. If your shop is only 12 feet away and you sort of caused it, just fix it.

It’s only a 4 foot wall? That’s easy as shit.

Yep, that's the neighbor's thought process.  I can't reason with this.

That would be my concern. If $2k gives you piece of mind and not sliding into his house into the future, it's money well spent. I would fix the wall for myself, the neighbor can piss up a rope.

is sheet piling an option? if not, grade it, add some geo-matting, and riprap the grade to stabilize it? having a copy of previous cease and desist letter on hand would be helpful, if he goes johnny-law on you.

I really don't feel that anything we did on our side caused it, intentionally.  My stance here is that we were really just putting our yard back the way it naturally was to begin with at its original grade.  
The neighbor talks with me as if our dirt shouldn't even touch his wall fence at all, like I should build a retaining wall to protect his fence.  He's nuts.

I'd do whatever it takes to make sure all the earthworks required to maintain the integrity of my property was on my property.

Clearly you can't count on that jackwagon to build a reliable solution.

Help me out here, what is sheet piling?

Call him up, fart in the phone & hang up

What does your HOA have to say about it?

Unless you build a retaining wall out of large stones on an angle, they will all fail with time. Cinder block retaining walls are all temporary unless reinforced.

What about whatever code-enforcement entity that has jurisdiction in your area? He may be in violation of some construction statute. They could make him rip it out

Burning bag of poop no longer a useful tactic?

Get your dirt guy to level and pack your side really well and let the old guy worry about his own stuff.  Sounds like he’s up there in age so shouldn’t have to worry about him for too long anyway.

If they had not graded your property to begin with 16yrs ago this likely would have been a non issue

You need some concrete waste blocks/ mafia blocks.

Put something next to the wall on your property that is worth some money but fragile.

When his wall collapses, since it is 100% on his property, but falls onto yours, you can get full replacement value.

If there is sentimental value, you could get more!

Win/win.

Do you trust your concrete guy?  If you do, then trust his judgement.

Prepare the way buy having a lawyer send a letter to him, stating your concerns about the fence.

Paper trails are important.

As you know a good wall requires lost of excavation and build back up in layers. Some pics would help but if my property wasn’t in danger I would let it ride for as long as I could.

You need to talk to an attorney and a civil engineer.

Use imgur to host pictures or send a few to me and I will do it.

Do you have a regional building department that may be able to force him to fix the hillside with an engineered solution?   If not, then you need to implement an engineered solution.

Do it right...not what seems ok.

Is it @ scw?

If I am understanding this right the neighbor changed the original grade of the land leaving a stair step right on the property line creating the problem in the first place. He should have moved the stair step far enough inside his property line so that he could have controlled the backfill, installed deadmen, and water drainage provisions. Instead he creates a high maintenance situation right on the property line and on top of that does a poor job of it. I side with the OP.

You add overburden pressure to the retaining wall by adding soil to the grade above the wall.  The neighbor did not build a proper wall.  Even at 4'-0" you need a concrete foundation over at least 6" of compacted gravel.  The CMU blocks should have been reinforced and fully grouted with a drain behind it. The soil behind the wall should have been gravel to allow the water to drain with a barrier to prevent dirt from flowing into the grave.

That's what I'm thinking

Sounds right to me.

This...

Then, piss along the property line to mark your territory.

This is where I believe your neighbor has a leg to stand on.  See the red text above.
Was the fence standing prior to soil being pushed up against it?
Was the  soil that was pushed against it pushed onto your neighbor's property?
Was there ever soil up against the current 'timber-cmu' wall before your grading contractor pushed soil up against it?
How far from the property line is the back of the wall?
From your description above, it sounds like your grading contractor damaged the wall.
The construction of the wall and whether it will retain soil is not really relevant if there was no soil against it before the grading contractor pushed soil against it.

If I am not understanding the events and time line, disregard all of the above.

From your description it doesn't sound like the wall previous wall or current wall was ever constructed properly to retain soil.

I think I'd probably do two things.

1. Hire an attorney and send a letter telling the neighbor that his shitty wall is harming your property.  Leave it open that you might continue to pursue this avenue.

2. Check the price of gabions and appropriate size rock to fill them.  Figure out where the excavated soil will have to go too.  Then make a plan to own the solution eventually.

if it's a "fence" and located ON the property line then he is probably obliged by statute to split the cost with you (I dunno your state laws, in Iowa that's the case anyway).

Personally, I'd get a bid to fix it correctly/install a proper retaining wall and offer to split it 50/50 with him.  If he refused then I'd do nothing and ignore him.

sheet piling is corrugated steel sheets, driven vertically into the ground, to prevent the ground from moving into another area. commonly used to keep the earth from moving into water, or separating elevations in grade.

sheet piling pics