Constructing adjacent to an existing CMU Wall

[Okiryu]

Hi all, our client wants to build a small house adjacent to an existing CMU wall which is old and showing some cracking. However, excessive deflection or settlement was not observed. See attached photos so you have an idea of the wall/site conditions. I expect that this wall is retaining clayey soils and there is not groundwater in the retained soils however, during rainy seasons I think that there is some water infiltration from the garden of the adjacent house which this wall is retaining. I expect that the CMU's are not fully grouted and there is vertical reinforcement @ 400 mm O.C.

I am looking at options for construction adjacent to this CMU wall. The site is not too big so space is a prime. One of the early discussions was about putting the new house adjacent to this CMU wall so the wall of the new house can serve as a "new retaining wall". If the new house is placed at the other side of the site, then we may need to build a new wall in order to protect our client's property.

I am assuming that nails or any other reinforcing options for the existing CMU are not possible since I think that the neighbor may not allow to touch his wall.

Any ideas for dealing with this CMU wall in order to allow for new construction? Any other issues that I may need to look at more closely?

Thanks !

 

[oldestguy]

You have been a member here for a long time. How in this world do you expect any reasonable answers by giving no specific detail about this wall and the site. No cross section, etc. I'd edit it with many specific details and maybe you can get started on this as an an engineer.

 

[PEinc]

Okiryu, you never said who owns the wall or on which side of the property line the wall is located. If the wall belongs to the neighbor, you really can't remove it and replace it with the proposed foundation wall without permission from the neighbor. If your client builds the new house away from the wall and the neighbor's wall falls over, isn't that the neighbor's problem? If the wall belongs to your client, your client is free to remove and rebuild the wall or is free to strengthen the wall as required. Your client would also be responsible if his wall falls over.

http://www.PeirceEngineering.com

 

[SlideRuleEra]

Okiryu - With the neighbor's permission, construct a gravity retaining wall in front of the existing wall. Fill the space between the walls with compacted soil as the gravity wall is built. The combination of the existing wall / compacted soil / new gravity wall should act as a single (very thick) wall. The segmental blocks are self-draining at all joints.

I did this for a 4' high existing, rotting wood retaining wall 13 years ago, using only the retail version of blocks. It continues to perform as expected without deflection. Note that there is a mature magnolia tree surcharge load on the wall. These photo show the existing wall and the gravity wall under construction. The gravity wall is full-height, the wooden wall is completely buried.

Edit: Deepest excavation, performed one block at a time: 8" deep, about 18" from the existing wall.

http://www.SlideRuleEra.net

 

[oldestguy]

Digging next to a neighboring lot and a wall there involves some legal things. In my area you can dig right next to it and any damage is not your fault if the wall caves in as long as the hole is less than 8 feet deep. If you go deeper you are responsible for the other side staying there.

 

[Okiryu]

Thanks all for the responses.

@OG, sorry about the lack of information. I attached some photos with my notes in my post and was hoping that could help for the discussions. Apologize I did not mention about that attachment.

@PEinc, the wall is owned by the neighbor and it actually delineates the property line.

@SRE, a new wall was one of the options but we were worried about undermining the foundation of the CMU wall when excavating the foundations of the new wall. Perhaps this can be solved digging and constructing the new gravity wall in small sections...

Thanks again !

 

[r13]

What is the foundation to be located, elevation-wise? Does the proposed building includes a basement? Did you do digging to find the base elevation of the existing wall?

 

[Okiryu]

retired13, thanks for the reply. I expect that the bottom of the footings may be within 1 m below the existing ground elevation (elevation ~43 m based on the attached photos). No basement for the proposed building. We did not verify the existing wall foundations yet.

I was thinking on helical piles if excavations for shallow foundations adjacent to the existing wall become complicated. Our local rigs for helical piles are small and can install the piles close to existing structures.

 

[r13]

If the new house is placed at the other side of the site, then we may need to build a new wall in order to protect our client's property.

I would seriously consider this option, as building the new wall against the neighboring retaining wall is costly, and may have undesirable consequences, also, greatly restricted the natural light source.

I would find the existing footing depth, and propose a stone wall up to EL. 45.7 with a shallow foundation.

 

[PEinc]

If the new house is placed at the other side of the site, then we may need to build a new wall in order to protect our client's property.

If your client is building a new house at the other end of his site, why would your client need to build a new wall behind the neighbor's wall to protect his own property? Two walls right next to one another? How would that work? Your client would need permission to tear down the neighbor's wall and on whose property would the new wall be built? Build at the far end of the site and forget about the neighbor's wall (and don't surcharge it).

http://www.PeirceEngineering.com

 

[Okiryu]

retired13, thanks for the input.

PEinc, the existing CMU wall is cracked and may present some risk in the future (although large deformation of the wall was not observed). That's the reason to construct a new wall next to the existing one. This is in Japan so it may be a strange case but instead trying to bug your neighbor, the owner prefers to protect his property and keep it safe.

 

[r13]

Again, I call for finding the footing of the existing wall, which may have been set on your property. Record the present condition of the wall, and notify its owner before construction. I guess there is a garden behind the wall, pay attention to trees that can damage the wall. What is the frost depth in the local, around 1 meter?

 

[Okiryu]

retired13, thanks again and yes, I agree with your recommendations. We will need to check the foundations of that wall. There is a garden at the retained side but I do not recall any big trees. We do not have frost depth for this site.

 

[PEinc]

Okiryu, I would be concerned about damaging the neighbor's wall if I tried to build a new wall immediately behind in front of his existing wall. Let the neighbor fix his own wall if it ever falls over. Stay away from it unless your client really wants his house close the the neighbor's wall and you and/or he know everything about the existing wall. Also, isn't there a required setback distance for the new house from the property line (existing wall)? You said that space is tight on your client's lot. If you build a new wall in front of the neighbor's wall, you will be wasting some precious space.

http://www.PeirceEngineering.com

 

[r13]

No frost concern? I thought Japan can be quite cold, maybe differ by region. Anyway, it is a good news that if you consider to build a wall for enclosure purpose, the foundation of a half height stone wall wouldn't be getting too deep to disturb the footing of the existing wall. By selecting the right material, the wall can be architecturally pleasant, even in mix with the remaining retaining stick out above.

 

[Okiryu]

PEinc and retired13, thanks much for the input. I will need to talk with the client and see how it goes... thanks again!