Combined fence and retaining wall

[pedro the swift]

Greetings to all.
I am in need of some advice on what I can do to repair/replace my combined retaining wall and fence.
THe fence posts abut the neighbours besser brick retaining wall and have wooden panels retaining the soil on my side. I dont know how deep the posts are or if they are properly secured on my side. I doubt it though.
The fence needs redoing and I want something that will last and want to do it properly. I dont know if I need it to be engineered since it is not a continous retaining wall as such cos the bricks are on the neighbours side. Total height would be over a metre but I doubt that the brick wall is well done enough to permit more height to be added to it.
I envisage some sort of posts on my side with concrete panels as the wall but I don't know it his wall will stand the pressure.
Has any one of you extremely knowledgeable people done something like this before and what would you suggest as a reliable long term solution. Thanks in advance. Photos attached.

[wattlewemake]

Pedro,
I have a similar setup to your yard. When I bought the house the building inspection showed that my fence wasnt 100% legit. After consulting an engineer he said it was wrong and gave me a list of options to fix it. One thing he did say though was that if the combined wall height was 1m it had to be an engineered wall, which makes it expensive.

Shane.

[Bleedin Thumb]

Pedro, I take it photo 1 is taken on your side and 2 & 3 from your neighbours side?
I would bolt Galv. posts to your neigbours side of the retaining wall (the wall probably has a footing so you won't be able to go lower).
Then bolt your rails to the posts.
It means your fence will move a bit over to your neighbours yard so they may not like it much.. see what they think?
Is that a PVC pipe running on top of the wall?

[mic-d]

This is just the way I would do it. Dig the fill on your side back off the old sleepers and then demolish the fence/retaining wall. Cut the posts off at GL and sledge hammer them below GL if they can't be levered out. Rebuild the fence along the same line with the new posts offset from the old post positions, using 100x100 treated pine posts at least 600mm in ground. Batten screw 200x100 treated pine sleepers to the back of the new posts. Backfill the retaining wall, ideally with a bit of gravel and ag pipe and geotextile (bidim) and then finish building the fence. If the retaining wall needed to be higher or looks higher than it is, then you could use 200x100 treated pine sleeper buried on end at a slight angle backwards as independent posts for the retaining wall and either put the fence in front of it or on top of it.



Cheers
Michael

[pawnhead]

That wall probably isn’t ‘core filled’, i.e. no concrete in the holes, and no steel reinforcement horizontally and vertically. That’s what an engineered retaining wall should look like. It should be hooked in with continuous steel bars, (min 12mm) right into a concrete base that either hooks under your side or on your neighbours side (or a bit of both), (and with higher walls, down in to rock with galvanised bars epoxied into holes drilled in the rock). It’s 800mm high and with the extra on top it would be 1200mm high. It looks like they’ve backfilled with blue metal after they’ve built it but it shouldn’t have bulged in the middle like that if there was horizontal bars laid on each course, then filled with concrete. It’s pretty straight in the horizontal direction so there could be ‘reasonable’ footing with some steel in it underneath, but there’s no telling unless you dig a test hole to see what’s there.
To do it properly, tear it all up and you may save some of the blocks by chiselling / grinding off the mortar but it might not be worth it if they’ve used a decent cement. Jackhammer up the footing, then call an engineer, or rebuild it as I’ve described it should be. If you did everything yourself it might cost you five or ten grand. To get an engineer and a builder might cost you ten or twenty, I don’t know how long the wall is. Then build a new fence on the steel brackets that you've cast into the wall. Add another grand for that and a hundred for the brakets if you do that yourself.

As for a quick fix,


Hmmmm,

edit; - Of course it may be a properly engineered wall that's just had a lot of stress. Test if the cores are full of concrete. If they're not then it will keep moving till it falls apart.

[Deanom]

Pawnhead is right on the money. That retaining wall on the neighbours side wall is no good. It may of performed ok before you added your surcharge to the wall (additional soil), but now the wall is visibly distressed (see photo where wall seems to have a point of rotation mid way up in the besser course and control joint in wall shows horizontal displacement) and will most likely continue to fail in the distant future. Had it been core filled, reinforced and built off a bigger than necessary propper footing, you may of been able to extend it slightly with no problem, but as it stands now it will fail.
You only really have two options:
1. Demolish the whole lot and rebuild it. It will need a new footing as the besser footing will be inadequate for the height of the existing fill. You can only hope your neighbour might go halves with you on the cost. A post and sleeper add-on on your side or his side wont help your problem. It will just waste your money.
2. Instead of removing the neighbours wall and building a replacment, you could also remove your timber wall and build a slab say (1.5m wide 200 thick and reinforced) to tie back into your site and add a reinforced besser block wall on top (say 3 courses max N12s - 600 vert N12-400 hor) however I wouldnt do this as your neighbours wall is already in the throws of failure.
I am an engineer and have performed numerous retaining wall calcs and designs. Although Option 2 should work if the slab keys into the existing wall, I wouldn't certify it or recommend it.

[pawnhead]

2. Instead of removing the neighbours wall and building a replacment, you could also remove your timber wall and build a slab say (1.5m wide 200 thick and reinforced) to tie back into your site and add a reinforced besser block wall on top (say 3 courses max N12s - 600 vert N12-400 hor) however I wouldnt do this as your neighbours wall is already in the throws of failure.
I am an engineer and have performed numerous retaining wall calcs and designs. Although Option 2 should work if the slab keys into the existing wall, I wouldn't certify it or recommend it.

That sounds like a reasonable 'uncertified' quick fix, but I'm just a builder so I'll bow to your wisdom.

I might just add that it's the responsibility of whoever altered the existing ground level to fix the problem. If your neighbour has dug his side out to build the wall, then you've added the extra on top putting even more stress on it, then it looks like you may share the responsibility.
However, if you just added 200mm to your side, then the sleeper arrangement should have been adequate if he'd built the wall properly in the first place, or if he'd left the ground level where it was.

A good heavy rainy spell could bring that wall down. Wet earth puts a lot of pressure on a retaining wall, and if you just built a new fence there, then it would go down with it.

edit: - I wouldn't park any cars on that grass next to the wall either.

[pedro the swift]

Hi to all, Thanks for the replies. Lots of good info there. I dont think it shows up in these pics but as you may see I have had the pool filled in and it looks like the mini tippers coming and going have added pressure to the besser brick wall and caused it to sag outwards about 10-12mm in places. I dont think the neighbour is impressed and it looks like I may be up for repairs so I will have to get some quotes and engineering done. Probably may as well do the whole fence at the same time.
I dont think the original wall was properly done or has rebar in it in spite of what neighbour says.( he isnt the sharpest when it comes to handyman stuff). I will check to see if my home insurance will cover consequential damage like this. I doubt if the contractor doing the filling would come to the party.
One suggestion made was to build a new retaining wall back from the fence onto my property and then redo the fence against the besser brick wall. It would be expensive and reduce my side drive clearance but would reduce load on his wall. I dont know it it is possible to repair his wall without a complete rebuild.
I will need to chase up some engineer types to give me some idea on what would be the best course of action. Stay tuned.

[pawnhead]

I dont think it shows up in these pics but as you may see I have had the pool filled in and it looks like the mini tippers coming and going have added pressure to the besser brick wall and caused it to sag outwards about 10-12mm in places. I dont think the neighbour is impressed and it looks like I may be up for repairs so I will have to get some quotes and engineering done. Probably may as well do the whole fence at the same time.

Like I said. If your neighbour is the one who dug down from the existing ground level, and built the wall, then it's his problem to fix it. You're allowed to drive a truck on your property if you need to. If the ground level hadn't been altered in the first place, then the trucks probably wouldn't have done any damage. Of course they may have bulged the ground, or cracked a path on his side, in which case you'd be up for it (a lot cheaper than building a new wall), but if he's dug down and built a dodgy wall, then it's his problem if it falls over when you drive a truck on your side of the fence.
Of course the extra 200mm of fill on your side could be a contributing factor, if you or the previous owner have put it there.

I dont think the original wall was properly done or has rebar in it in spite of what neighbour says.( he isnt the sharpest when it comes to handyman stuff).

It should be easy enough to find out if they're full of concrete or not. They usually screed the concrete level with the top of the blocks, and it looks to me like they're just full of blue metal (gravel), in which case there'll be no re-bar in them either. You should be able to find out where the original ground level was from old plans, or sub division diagrams. Whoever changed the levels and built the wall is responsible for it.

I will check to see if my home insurance will cover consequential damage like this.

They'll want to know who built the dodgy wall in the first place, if they've got their wits about them. They're not in the habit of replacing bodgy work with expensive, properly engineered stuff. You could build yourself a tin shed, and get it replaced with a house after the first storm blows it over if that was the case.

I doubt if the contractor doing the filling would come to the party.

Not if you asked him to drive his truck in there to fill your pool he won't

One suggestion made was to build a new retaining wall back from the fence onto my property and then redo the fence against the besser brick wall. It would be expensive and reduce my side drive clearance but would reduce load on his wall.

I doubt that would be much cheaper than tearing the old wall down and rebuilding it properly.

I dont know it it is possible to repair his wall without a complete rebuild.
I will need to chase up some engineer types to give me some idea on what would be the best course of action. Stay tuned.

I'm sure they'll say the same as Deanom has suggested. Tear it down and start again. His #2 suggestion would be the cheapest, but I doubt that any other engineer would suggest that, or certify it. It would probably hold up as he said, but why would an engineer risk it failing since it's easier for them to cover their @rse and just tell you to tear it down and start again.

It won't be cheap.