Retaining wall safe distance?

[Zentelis]

We recently had a 4 car garage (960 sq. ft.) built into the side of the hill we live on. As such, we had to have a retaining wall built.
My question is, is there a safe distance for a retaining wall? Our contractor built the stone block retaining wall right up against the side of the building (it's an aluminum sided pole building).
During the last heavy rain, water leaked into the garage through the floor at the retaining wall. Also, the wall is leaning against the building now.

We've had a number of folks with construction/excavating experience tell us that the wall is unacceptable, that it should be built at least 5 feet away from the building. Some even told us it's unsafe.

I don't know any technical details, but the wall was built with (apparently) typical retaining wall blocks. The wall is about 5 feet high and covers one whole side of the building (20ft) and extends half way down the back of the building (12ft).

Any thoughts? Thank you!

 

[GeoPaveTraffic]

I don't know of any standard setback between a wall and a building, but I would say it is very unusual to build a wall adjacent to a building. If the wall has moved to where it is touching the building, then you have a problem that needs to be addressed as soon as possible.

 

[MSEdesigns]

You can have buildings at the wall. What needs to be addressed is the amount of load the building will impose to the wall and design for that.
If your wall is leaning back (toward the retained soil) you probably have a poor compacted material which is now consolidating and causing the movement on the wall facing.
You do not mention any soil reinforcement. This size wall looks simple but with a surcharge load like the one you mention, it will probably require one or two layers of reinforcement.

 

[cvg]

Has the entire hill shifted? If so, you can't expect the retaining wall to hold it back and you shouldn't have built your garage so close to the hill.

Otherwise, it appears that your wall is failing. I would call your contractor and ask him to repair / replace the wall.

 

[jdmm]

Zentelis,

First, you do not want to have a contractor design a retaining wall for you unless they have retained an engineer on your behalf.

Second, you do not (normally) want to design a retaining wall that has to support a building load. That is, you do not want the building performance to rely upon the performance of the retaining wall. If the building performance depends upon the performance of the wall then the wall must be designed to the same standards as the building (ie earthquake, servicabity etc.)

From the information you have presented, I would suggest that you have a geotechnical engineer review.

 

[DRC1]

If the building is 5 ft from the wall, the wall will see very little if any load from the building. However, should the wall move, the soil that moves with the wall could extend out past that. I assume the wall supports the soil on which the garage sits, ie. the garage is behind the high side of the wall. The fact that the wall is leaning toward the house indicates the bottom kicked out. What this indicates is that there is a semi circle of earth trying to rotate under the wall. The rains increaseed the weight of the earth and lessened the restraining force of a weak layer. The wall probably needs to be deeper. You should have a geotechnical or foundation enginer look at it. Don't get a structural, because it is not a structural problem. He can reccomend how to stabilize the earth temporarily and how to fix the wall. My guess is that the building can be supported on screw piles while the wall is rebuilt with a deeper toe.

 

[born2drill]

DRC1, I think you have things backwards. The way I read it, the garage building is on the cut side of the wall. I'm not sure how else the wall would be "leaning against the building." So I don't think we're dealing with a failing wall that also is at risk to undermine the garage.

Still, this wall is failing and something needs to be done. I doubt the wall was ever really designed by anybody in the first place. Zentelis - notify the contractor, find a good local geotechnical engineer, and call your lawyer.

 

[dpa]

I think born2drill is right. The garage is at the base of the wall.

It's amazing how much there is to know in life. The contractor probably did this in good faith but has probably never heard the term 'geogrid'. Maybe there should be mandatory classes for anyone applying for a contractor license where they just have to sit and watch a few videos that illustrate what is involved in various projects along with some examples of how contractors and homeowners have screwed themselves by not getting a building permit.

I know of an older couple who need to move from the country to the city because he had a stroke but they can't sell their house because they made additions without a permit and there are structural problems.

Take born2drill's advice. Maybe the lawyer doesn't have to be in on it from day one, however.

Sort of off the subject but no by too much.

DPA

 

[epongra2]

With regards to a standard retaining wall "setback", it depends on the geographical area and the building codes in place in that area.

Here in Southern California, a rather basic structural (i.e. residence, garage, etc.) setback is well-established for an ascending slope condition. The structure is to be setback a distance of H/2 feet (H is the height of the slope above the existing or proposed building pad grade), with a maximum setback of 15' and a minimum setback of 3'. This would also apply in the situation above where it is desired to construct the retaining wall after the construction of the garage. By the way, the garage would not be exempt from this Code provision, even though it is considered a "non-habitable" structure.