Removing A Retaining Wall

Cache

Ok all you excavation pros. How would you go about removing this wall?

Situation:

Older home: mid 1960s
Retaining wall: 55' long X 8' high X 12" thick
Material: poured concrete

Wall starts at front property line and runs along driveway and side of garage until terminating in backyard. The section that runs along the side of the garage is located approx. four feet away from the garage. At least that is the case at the base of the wall. Eight feet higher at the top of the wall, the hillside has pushed it in so that the top of the wall leans in almost two feet. Here in northern Utah we have heavy snow and roudy freeze/thaw cycles.

Not sure about the use of rebar when the wall was built, but I'm sure the footing was undersized or improperly designed. Plain and simple, it could last another 10 years or another 10 minutes, but when it comes down it takes the garage with it.

Obviously, excavators want to park a track hoe on top of the wall and knock it out one scoop at a time. The conditions suggest the possibility that the weight of the machine will cause the wall to fail. Also, the neighbors would have to agree to the hoe tearing up their yard, which is unlikely to happen. The hoe can't come at it from below because it will destroy the driveway and the powerlines are so restrictive that they would probably have to be taken down to work with a machine that large.

I had suggested using a rubber tire backhoe loader, starting at the front boundary and remove a 5' wide swath of ground behind the wall about 7' at a time. Brace the wall. Then use the bucket on the backhoe to push the small section of excavated wall toward the hillside. With any luck, the use of rebar would be light and that should break up the wall pretty easily.

Other suggestions have been to do the same kind of thing as above, but use a jackhammer to break up the wall instead of just pushing it over with the shovel. Also suggested was using a skidsteer with a concrete breaker attached.

What do y'all think. What is the most efficient way to remove this wall without it falling into the house in the process or costing $20K to do?

dlcj

I think you idea is the only way. That in conjunction with a skidsteer with breaker attachment. Either way you'll have to replace 5' of the neighbors yard anyway.

Cache

It would appear that the 5' or so that will need to be removed is actually on the HO's side of the property line. Neighbors don't really have a choice in that case. The developer evidently wasn't very good at math and angles. The lots all wrap around a hillside and none of them are square at all. Consequently, surveying the lot is nearly impossible as the developer just threw the houses in as he saw fit. At this point we don't really have any idea where the property line is in relation to the wall. The neighbors need to face the reality though. If that wall comes down during spring runoff, their yard and driveway and possibly some of their garage come with it.

concretemasonry

I can't see the situation, but have a possible suggestion.

If you work from end to end (front to back) in sections, it moght be good the break/crack the wall into managable lengths (7-8 feet), so what your are removing does not cause an unintentional effect on the rest of the wall. - It might help to keep thing under control with a touchy situation.

Breaking/cracking of the wall could be by sawing partially or by a jackhammer. You want to create a weak line, not really to totally separate into individual sections. For a cantiler wall, the most and heaviest steel is usually vertical and the horizontal steel is less.

Just a suggestion.

__________________
Dick

Engineer, designer and consultant recently active domestically and internationally on construction and design in about 35 countries.

neolitic

You should try and get the customer and the neighbor
to split fees for a licensed surveyor.
Even if they don't care about the PL now,
it could make things messy when one of them
sells.
Myself, I would never get into that much work
without knowing whose property I was working on.
You are exposing yourself to some heavy trouble.
At the very least one of them surely had a
mortgage survey that at least let's you have a clue
about PL in relation to the house...
just not very precise.

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(Sorry....it seems there really are dumb questions)

Cache

I agree, but a surveyor who already did a survey up there some years ago on a neighbor's lot has left them all very confused as he claims the survey will also be subjective and will not match the county plat maps; indicating that for some reason there isn't much of a reference point to begin a survey from. The landscape is very irregular and it appears that precision wasn't a top priority when the developer originally built these homes.

There is no doubt that the wall is entirely on the property of the HO. Setback requirements here are 8' minimum and usually closer to 15-20'. If this were to be decided by a court, the likely outcome would be a new property boundary located 8' from the side of the garage. Under normal cirucumstances, the wall would be the responsibility of the person who's lot is being retained as it would have to be placed before construction of the building. In this case, the neighbor's home was built first requiring only a small 2-3' wall on the west side. When the site was prepped for the HO's home, an additional 6' had to be removed from that east side of the lot. So the people who's lot is supported by the wall have no financial responsibility to fix it, even though it would be a complete mess for them if it failed.

Essentially, there is a good chance that part of what the neighbors consider to be their property is actually the property of the HO. I can imagine a 2-3' error in either direction, but in either case that would still leave the wall on the HO's property. Luckily, I am not being contracted for this job and I bear no liability for any of it. Unfortunately, it is the responsibility of a very close relative so I bear the responsibility of relation.

Cache

That's almost the exact conclusion we are coming to. Working front to back and using a concrete saw to seam the wall for a more precise break in about 5-7" sections.

One other detail is my opinion as to why the wall hasn't failed yet. There is something of a slight convex curve to the wall in relation to the HO's home. Or with reference to the hillside, the center of the wall is set deeper into the hillside, with the ends curving/curling slightly around the HO's home to the downhill direction. I think this is adding stability that would otherwise not be there, and if the wall were absolutely straight it would probably have already failed. If we then remove one end of the curve it would reduce the bearing capability of the center of the wall. Our plan is to use lag bolts achored into the driveway and retaining wall to build a series of braces.

RPC470

#1 get a surveyor to locate the property line and stake it (no big deal probably only $500 plus or minus
#2 what are you replacing the wall with? If you are using blocks such as keystone or unilock you will need to put in geogrid which means digging back as far as 8 feet. If you are using concrete you will have a lot of excavating to do i read it as almost 12 feet from high side.... strike that you are in Utah... You have to dig 5 feet deep than another however many feet to go below the frost line.
#3 get an engineer on this job big time
#4 here is something differenet I have had to do this before and it works. dont worry about where your wall height is less than 4 feet. go in with an excavator on the top the way your contractors recommended then where it is greater than about 1 foot behind the wall to depth and place sheeting in there to hold the bank back. you will have to do this anyway.... I wouldnt have a 8' tall sheer face looking over a nieghbors driveway huge liability. you chould have an engineer design your sheeting for this becasuse it all depends upon soil types for you situation etc. I am not sure that you will be able to pull this off for less than 20k honestly

Cache

1. Survey quoted twice at $1200.
2. Boulders are preferable. That will reduce the cost of the wall significantly. He is also wanting to change to a couple terraces instead of a single 8' wall. Three 2.5' walls should do the trick. So the debate becomes one of boulder size.
3. Architects/Engineers estimating for a poured concrete wall have suggested $20K. Excavators and boulder retaining wall landscapers have all bid around $7K.
4. I can't go in behind the wall. The neighbors don't want their yard torn up. As to your other point. There wouldn't be an 8' sheer wall looming over the neighbors property, it would be looming over the HO's property. I don't think the excavated wall would be in danger of coming down during the 3 days that it will take to construct a new boulder wall. I dig plenty of 8' sheer faces for basement foundations that sit there for weeks with excavators perched on the edge without coming down.

gregj

Have you confirmed the actual dimensions of the wall? If the 8' is above the HOs grade how deep is the wall below grade (below frost presumably)? Is there a horizontal component to the wall (a cantilever under that 8' deep backfill) that you will be removing? I would be surprised if all there is to the wall is an 8' high, 1 foot thick wall sitting on grade.

Cache

If the wall was done correctly the footing would be 30" deep to get below the frost line and there would likely be a 3-4' canted footing. Problem is that there is little evidence suggesting that it was done correctly, otherwise it wouldn't be failing. The wall is actually about 7.5' above grade. It could be the appropriate 9' tall with a 3' wide 12" thick canted footing. OTOH, it could simply be an 8' wall with a standard 20" wide footing, as I have no idea if the original installers knew what they were doing.

He doesn't yet own the property so we have no way of determining that info. We have to simply assume that the wall was done correctly and that excavation will require the removal of a canted footing.

RPC470

are you really willing to risk installing an un engineered 8 foot high wall made of boulders? your subs arent responsible for this you are! I would run from this one and not get involved let someone else takethe liability in NY anything over 4' needs a licensed engineer to sign off on it. Here is an idea... can you leave the wall be, build a new one in front of it and just groute the void with say k-crete?

RPC470

oh and as for your comment about having 8' sheer faces when you dig foundations that is on a construction site.... this is a home if the bank collapses with a foundation you redig it if this bank collapses what will happen. will it have any adverse effect on the neighbors property or the HO's property? and most importantly how good is your insurance?

Cache

That is a good idea, and I really wish I could simply build a new wall in front of it, but the walkway between the wall and garage is already too cramped.

An 8' boulder wall would require engineering here too, but not three 2.5' boulder walls. He is thinking he'll do the first 2.5' wall three feet from the garage wall, then cut a terrace back about 2 feet. Then another 2.5' wall and again a 2' terrace, followed by a final 2.5' wall that should end up right on the property line. Anyway, I'm not taking on any liability on this one. I'm not being hired for the job. A family member is trying to figure out the best way to do this.

concretemasonry

The 2.5' wall with only 2' set backs and then another .... adjacent to another home? That will not fly unless you have a dumb engineer and an even dumber permitter/plan approver or inspector. Even with mafia blocks, you would have a hard time. The short set-back "ruse" solution is a classic and is well know to most people.

Just make sure you let your family member the predicted challenges and the possible probelms that can occur when digging close to another home and on the property line.

Jobs like this can appear to be too simple, especially if you have preconceived ideas and solutions. If you have basements, the possiblity of problems go way up, but underpinning a slab on grade that has lost some support is not cheap either.

The $20,000 cost figure may not be practical for both removal and replacement. If you have a good engineered wall of segmental retaining wall block, your family members could do the replacement portion of the wall if they have time and are willing to work and rent some equipment. With a good design, the construction is just a lot of work until you are up a few feet. A contractor probably not be able to do both removal and construction for the suggested price.

__________________
Dick

Engineer, designer and consultant recently active domestically and internationally on construction and design in about 35 countries.

tgeb

Mini ex with rubber tracks equipped with a hammer, and a skid loader to remove and load the debris onto a truck, or dumpster can, if no truck is available.

I won't even try to address some of the other problems you are dealing with there. With the exception that the neighbor may have no choice in the matter, but to allow access onto his property in order for the wall to be replaced.

__________________
Tom

www.gebcon.com

JPC2

I like the idea of scoring the wall into sections so it breaks where you want it for removal. You can be reasonably precise that way.

As for the wall itself, have you considered some of the landscaping block products? I've done HUGE, tall, long walls and terraces with them. Each course steps back a little and the slope gives the finished wall a "safe" feel. I would recommend added a reverse curve or serpentine to the design as this will help strengthen it. I've seen massive commercial and DOT walls done like this. Price is probably more than 20K though...

Cache

If I'm not mistaken, the neighbor's house is about 20' from the property line, not sure if that would change things. The segmental block is just a ton more expensive than boulders. I've seen the "terraced' short boulder walls many times and wasn't aware that it wasn't kosher.

dlcj

have you seen these walls? http://www.hilfiker.com/www/index.html I was quoted about $10.00 for a face sq ft of wall i want to build. My walls will start from nothing and and go 50' out to a corner hight of 14'. so an average of 7' for figuring. $7000.00 for the materials. no labor ,no shipping
Just a thought. they look great covered in vegatation

Cache

That would really be nice covered in some climbing roses with a continuous bloom. Definitely something I could suggest to him.