Retaining Wall

[sogreen]

Hi
I am planning to build a retaining concrete block wall 8 feet high. The wall length is 8 feet at the highest level then turns into 4 Feet. I have sandy soil and my location is on a slopped hill. The house is 100 years old and the retaining wall that was there is in pretty good condition. My landscaper believes that I will be okay by drilling Sono Tubes and then putting a concrete footing on top then rebar and concrete block going up to the desired heights. He also said that he will put in proper compaction and drainage every 4 feet to go out of the wall. Question is this: 1. Is he right, 2., how big should the footing be? (I read somewhere that for 8 feet high block wall you need at least a 4 foot footing). 4. Do I need to put some type of tie back into the existing soil? 5. can I use a geogrid of some sort?

thanks
Ivan

 

[msquared48]

Unless your "landscaper" is both a Geotechnical and Structural Engineer, no.

By code, any wall over 4 feet requires a structural engineer at least to analyze and design it.

Hire a Structural Engineer and fire the landscaper.

Mike McCann
MMC Engineering

 

[JedClampett]

Hire a strucutural engineer. Alternatively, you can get a Interlocking Block Wall manufacturer provide you with a sealed design, but either way, you're going to have to pay an engineer.
Eight foot tall retaining walls are not to be trifled with.

 

[cvg]

you need a permit to build this wall. 8 foot high retaining walls are not generally built using concrete blocks, 6 feet high is a typical height limitation. This is not typically a job for a landscaper, which in my opinion are the lowest level of contractor in the food chain.

Question is this:
1. Is he right, have him show you the calcs...
2., how big should the footing be? (I read somewhere that for 8 feet high block wall you need at least a 4 foot footing). possibly wider, but do you want to base this on "something you read somewhere"?
4. Do I need to put some type of tie back into the existing soil? probably not the best idea
5. can I use a geogrid of some sort? usually only used for fill construction

 

[CCox]

I agree with the other engineers. Lateral earth pressure goes up by a squared factor as depth increases. So, an 8' retaining wall has 4 times greater earth pressure against it than a 4' retaining. Hence, the code requirement for an engineer to get involved. A sloped grade behind the wall also increases the sliding. Down grade slope reduces sliding resistance. These site specific issues need to be addressed by an engineer.

Cody

 

[TXStructural]

You can build a wall with block, but it will be fully grouted, and needs to be designed. And it is not just about the wall, it is also about stability of what is behind the wall, like a house.

The design of a stable wall is not a trivial exercise, both because of soil considerations and the wall itself. Improperly designed or built it will rotate or slide (soil failure) or the wall itself can deform or completely fail.

 

[BAretired]

I agree with getting an engineer to do the design. An eight foot high retaining wall is nothing to be sneezed at. "Drilling Sono Tubes and then putting a concrete footing on top " is not a good idea.

Will the footing be subjected to frost on the low side? If so, heaving may be expected and the wall should not be tied in to the house foundation.

BA

 

[RFreund]

Your best bet may be to use a segmental block wall (search Keystone or Anchor or VersaLok, etc there are a bunch). Usually it is the most economical way if the site permits it. Unless this is a basement wall. Either way I would prolly give an engineer a call.

EIT

http://www.HowToEngineer.com

 

[concretemasonry]

A segmental wall may work and could offer many advantages, but it cannot be connected to a rigid structure (home) since it is flexible structure. If the home is close to the wall, the horizontal spacing may limit the practical height because of the need to place geo-grid.

The height of only 8' is not a problem. Within 3 miles of me, I have numerous segmental walls (no footings obviously) that are 12' to 20' high that form inside and outside curves to retain the soil form around buildings placed above and behind the SRW walls.

Normally, the height of a wall to be engineered ranges between 3' and 6' depending on the location for permitting.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[chicopee]

I agree with TXStructural about grouting the block wall and I would stipulate with the addition of rebar; having a well prepared base for bearing capacity, battering the face of the wall, anchoring the wall from sliding at the base, providing tie downs along the face of the wall, and having weep holes for drainage should also be considered. Nonetheless, you'll need a stamped drawing to submit to the municipal licensing board . But such wall will look terrible after a few seasons.

 

[hokie66]

chicopee,
A reinforced block retaining wall need not "look terrible after a few seasons". If the earth side of the wall is tanked (waterproofed), then you can use an acrylic coating on the visible side, and with maintenance every few years, the appearance is quite acceptable to most people.

 

[JAE]

sogreen - you need to go hire an engineer. This site is for engineers and not do-it-yourselfers.

 

[pbody]

Do control joints normally have vertical rebar placed in the CMU on each side of control joint?

 

[hokie66]

pbody,
If you are talking about this 8' high retaining wall, the vertical reinforcement would be at not more than 16" centres. So there would be a bar close to any control joint.

 

[chicopee]

hokie66, you are right about your statement but most owners will slap some coating and eventually the true nature of the wall will be revealed.