Residential Retaining Wall Repair

[pbc825]

I've been contracted to provide repair recommendations for a retaining wall between two residential properties. The retaining wall is constructed from CMU's that are filled with cement or grout. I didn't see any reinforcing steel poking out of the top under the caps. There are no drawings of the wall or the foundation systems for the two neighboring buildings. The highest differential soil height is about 60 inches. The worst angle from plumb is about 10 degrees which coincides with the maximum differential soil height. I'm contracted by the west property owner, and the east property owner is quite upset.

Wall is about 10 years old and recently a contractor compacted soils on the east side for a paving stone walkway.

The east neighbor is unwilling to do or agree to anything useful, so tying the top of the wall, pinning and excavating for a new properly designed cantilever wall, etc. is out of the question. As is doing anything to disturb the east property. The distance between the two building walls is about 8 ft and the eave overhang is about 2 ft. The plan as I've conceived it so far is to twist in screw piles (haven't decided on the spacing or pile details yet) and hammer down segments of steel plate. Complications include:

1. Headroom to the bottom of the eave is about 10 ft, so extensions will be required. Extension connections may interfere with wall plates.
2. I've never recommended this sort of repair before, so I have little experience with the execution of such a project.
3. Not sure if we'll have trouble driving the plates in with such little headroom.

I'm seeking advice on a few things.

A. Does anyone have experience with this sort of challenge with similar constraints? If so, what repair recommendations did you suggest?
B. Has anyone made a screw pile and driven plate wall? If so, what were the execution challenges?

Thank you in advance for any advice or wisdom.

PBC

 

[oldestguy]

Which is the up side and which side is lower? A photo might help.

 

[pbc825]

The east neighbor is on high ground. I've attached a photograph.

 

[oldestguy]

Photo helps. Next question is where is the property line? Assuming the wall is shared, and knowing that there was compaction done, the east maybe legally obligated in some way. This may be better first resolved by the attorneys. Off hand I'd say the east owner is obligated to to hold up his side and his load on it and the compaction work would come into the picture.

If it would be possible, the west may just let it fall, but protect his building from damage. The attorneys may argue that, since it is the predominately for east's benefit to have this wall and his loads are on it, the west may be in a good position for damage claims when it falls. That car load on part of it further shows the east's implications in causing the lean.

Without removing and replacing, the work of stopping further lean is likely to cost more than the replacement.

 

[jayrod12]

agreed with OG. It's the high side causing all the issue. Low side should protect from damage. Here north of the 49 we might not jump straight to lawyers but start at the home insurance companies. Both insurance companies, high side and low side have something at stake here and they may be willing to help resolve the issues.

 

[pbc825]

Thank you oldestguy.

The property line is likely right down the center of the wall itself. I'd have to ask for a survey or the advice of others to know for sure. The west property owner's contractor constructed the wall; therefore, they're assuming they're on the hook for repairs. I'll suggest consulting legal advice regarding cost and responsibility, but my experience has been that only the lawyers win when lawyers are involved. I agree that the wall is holding up 100% of the east property owners loads.

I agree that removal and replacement is technically the best method forward, and I may ultimately recommend that especially if the less invasive options aren't technically feasible. However, if I were to recommend a less invasive option do you (oldestguy or anyone else) have advice on how to perform such a repair? Even if the east owner is on the hook for the cost?

PBC

 

[pbc825]

Jayrod,

I'm in Canada as well.

All,

This sounds like the recommended option is to pin the east foundation system, excavate, and construct a well-conceived retaining wall. I'd argue that, if it works, my proposed option with screw piles and steel plate walls might be less costly. Does anyone share that opinion, or am I dead wrong?

PBC

 

[Doctormo]

The history of the retaining wall construction is probably important from a liability standpoint. Who was there first? I am assuming the east neighbor was there first and the west neighbor built the wall to develop his/hers property. The liability would probably be on the west property owner then and damage to the east neighbor's driveway as a result of the wall failing may be his problem as well. Now if the east property owner did something to change the wall loading condition after the wall was built such as the driveway in the photo then the liability might swing back to them.

 

[pbc825]

Although there's much to be said regarding the liability of each property owner, let us leave that to the lawyers.

I'd like to focus this thread on the technical aspects of the repairs. Any guidance in that regard?

PBC

 

[hokie66]

I don't like your chances of doing anything constructive to "repair" the wall if it is leaning at 10 degrees. I agree with others that the liability should be sorted out first. If your client attempts repairs, he will have accepted liability, rightly or not.

 

[Ron]

OG and hokie66 are exactly right. I'm not sure about the laws in Canada, but it is likely that only one of the parties actually owns the wall unless there is a cross-use agreement (highly uncommon in residential applications). Common walls are difficult to handle legally. I've been involved in several in the US, but they might be different. The lack of separation between properties is not something we would generally see in the states unless it was in a special zoning known as a PUD (Planned Unit Development).

Check with the lawyers, but I agree the high side has the liability and the low side can mitigate to protect their property.

 

[hokie66]

May not be helpful in this case, but where I live, there are local laws defining liability for retaining walls, and a Small Claims Court to enforce the law. Like Doctormo, I think the most common interpretation is that whoever built the wall and owns it is liable. If the upper block was filled and retained, then he owns it. If the lower block was cut, then that side is responsible.

 

[oldestguy]

While it may be costly, I'd ask of construction companies that deal with special geotechnical projects, since that experience and capabilities would help you to decide what to do. There are two companies, among several, that probably can comment on the situation and perhaps give some guidance. They likely do work in Canada also. Try Hayward-Baker or Schabel Engineering. They have WEB sites.

 

[Doctormo]

pbc825 - I only discussed the liability issue since the east neighbor is being a pain. He/she may be more understanding if they become part of the "problem" from a liability standpoint. The concrete work in the photo looks rather new so they could have loaded or disturbed the wall or at least a case can be made that they are partially at fault.

Your photo is not encouraging. The two homes are very close and I assume the property line is half way between the foundations which you will need to verify. The grade appears to step down as well going to the rear. Looks like the property line may be at the back of the exposed wall and I would assume you would have to confine your work to the west property if the east owner remains unfriendly.

The only "easy" way to solve the problem is with the cooperation of the east property owner. You removed everything from foundation to foundation and construct the appropriate retaining structure. If the fault is with the west property owner then he/she picks up the cost of replacing all the concrete on the east side and offers anything else necessary to gain cooperation.

Based on your dimensions, you only have 4 ft. to work with on your side of the property line in which is probably not enough to get any equipment in. There also appears to be utilities on your side also (AC, electric, etc). I would probably auger piles in with lagging to support the east side while removing the existing wall. However, there is no room to accomplish this with conventional equipment while staying within the property limits. You are looking at an auger that somehow has to go 10'-15' into the ground and soils that will support themselves while you are doing this. I have used some skid mounted augers for taking soil borings in tight places that might be adapted to such construction. Hand augering would seem almost impossible to me but then I am not 21 years old anymore.

The job is way too small to get any interest from the larger companies so you can only reach out to local foundation and wall repair companies that may have the proper equipment and experience to work in such close quarters. The first thing they will do is ask the neighbor if they can work on their property and how much it will cost for permission if they replace everything since that may be cheap compared to the alternatives. It is pretty much a no-win situation as described.

 

[pbc825]

Thank you all for your valuable input.

We'll be working on the east property owner's side of the wall. I'll keep you updated with the progress and what we decide to do.

Best regards.

PBC

 

[PEinc]

oldestguy, Schnabel Engineering is a consulting geotechnical engineer. Schnabel Foundation Company is a design-build specialty contractor. They are, and have always been, two different, unrelated companies, founded by brothers. I doubt that either HB or SFC would be interested in so small of a project, especially where residential owners are fighting. The simplest solution might be to just backfill the low side of the wall with crushed stone for most of the wall height.

http://www.PeirceEngineering.com

 

[pbc825]

I like the idea of filling the void. I'm privy to some photos that make this option unattractive for the west owners.

I've notified the client of the legal suggestions you've made, and I've provided two options for the contractors to investigate for feasibility. One is less invasive but less conventional. It involves screw piles (8" pipe, 14" helix embedded to 15' past the lower side's elevation spaced at 40" O/C) on the east side of the existing wall and hammering in 4' stiffened 3/8" plates on the east side of the piles. The existing wall could then be removed and replaced in kind with little to no structural significance. The steel retaining wall would be permanent.

The other option is more invasive but more conventional. It involves underpinning the high east foundations as required (I think the garage is on a shallow footing), excavating the void between the two buildings along with removal of the existing wall, and constructing a well-conceived reinforced concrete cantilever retaining wall complete with a shear key.

I'll update once the contractors give me some feedback.

PBC

 

[oldestguy]

With the screw pile alternative, do you have any soil data? With either, the garage footing info is needed. Have you explored bringing in a crane with equipment to drive H piles? Might be better at giving lateral support, since screw piles are mainly for vertical support.

 

[PEinc]

I would expect that backfilling in front of the wall, on the west side, would be the cheapest option by far. The backfill could be crushed stone, soil, or a combination of both. If necessary, the backfill could also be sloped down toward the west so that less fill is placed against the west foundation wall. The backfill probably would not need to be placed for the full height of the retaining wall. The other options sound very expensive and highly unlikely to be done.

EDIT: The wall may have started moving when the east's contractor compacted the driveway immediately up against the back (east) side of the wall. If the contractor used a heavy or vibratory roller, the large compactive effort could have moved the wall. Just because the west built the wall, it doesn't mean that the east isn't responsible. However, proving it could be tough.

http://www.PeirceEngineering.com

 

[hokie66]

It's not really just a void on the west side. Look at the photo. The backfill would be against a wall of the house, construction unknown. And there are services, including a heat pump and something else beyond.