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FMS 07-03-2011 01:49 PM

Retaining wall problem
I just recently had a cement block retainer wall built and have a question about it. The wall is about 5' high and is built of Diamond Pro straightface 8" x 12" x 18" interlocking, trapezoidal, cement blocks. It was built by a local landscaping firm. The wall is 50' long, is backfilled with rock and sand. The wall has a french drain on the backfill side. My concern is as follows: When first built the wall had a slight lean in toward the backfill side, which is normal as each block interlocks and offsets slightly. Approximately 2 weeks later 1/2 of my wall is straight, vertical, and the other half which has less backfill (therefore less weight) has retained its lean. I called the landscaper and asked if they had installed a geogrid (geo-stabilizer) since the wall was over 4' high (manufacturer recommends this). He told me no, that the wall did not need one. My question is this; is this wall going to continue to move and push over backwards or is straightening just normal and my wall is ok? I have asked the landscaper to come back out and check the wall but I suspect that he is going to say this is normal and I don't have anything to be concerned about. We paid a lot for this wall installation ($23/sq. ft) and I don't want to have the wall fall over on my neighbor's property 1-2 years from now when we will be stuck with a costly repair. Is there anyone out there who has had a similar problem and has any suggestions.

concretemasonry 07-03-2011 04:38 PM

The Anchor Diamond wall units have been used for years in the U.S. Those and similar reputable brands with approvals and testing have been accepted by by many for use a standards for contractors, DOTs, and municipalities in the U.S. and internationally for walls under 4' high but some areas put the dividing line at 5', but after that they must be engineered and can be used for up to 40' high walls.

You have to look closely at the installation methods and materials to see if it was actually done right right. With proper base, backfill material and drain tile (if used, but usually not necessary since the joints are open). Other wise put the contractor on notice of the problem, so they are responsible if there is a failure and they are still in business.


sippinjoes 07-03-2011 06:13 PM

Their website says max 4' without reinforcing. I've never heard of installing a wall and expecting it to move or tolerating any movement especially that soon

Edit: what was the sand for? Depending on use it could slow drainage and increase hydro pressure.

concretemasonry 07-03-2011 09:36 PM

sippinjoes -

Go back to sipping.

Sand can increase the drainage, but the velocity of the water drained may carry and silt or sand from adjacent materials down and plug any pipe or sleeves. The proper backfill is ideally a mix of sand and graded rock to provide a better drainage system and insure that wider area around the pipe or behind the wall can be dewatered. This dramtically decreases the lateral pressure on the wall and is commonly speced on earthen gravity dams because of the functional life and reliability. Anything like silt or clay would be the worst hing to use as a backfill.

The 4' was inserted in the product specifications since some codes have an arbitrary height limit of 4', while others accept 5' for dry stack gravity walls. Our municipalities usually have a standard plate showing a "canned" unengineerd design for use by the municipal employee crews, contractors and residents. The 4' in the specs is common for all recognized systems since it is conservative.

A segmental retaining wall (SRW to engineers) is classified as a "flexible" wall system that can move seasonally without loss of strength or stability and that is also why it is recommended to NEVER use a rigid concrete footing that can be destroyed by frost/freezing. The general concept is accepted, proven and is used internationally in all conditions.


sippinjoes 07-04-2011 06:45 AM

Moderate use of sand makes since. I never considered putting it behind the wall.

I would think the acceptable movement wouldn't be lateral? Sounds like frost/freezing would move it mostly vertical and if on a good footing never really be noticeable.

I guess I need to state I'm not an expert (or maybe I don't need to state). Thanks for correcting me. I really don't want to mislead people. Just want to learn myself.


jomama45 07-04-2011 04:24 PM

Is this a straight wall where it is clearly evident that's it's actually moving, or have you taken actual physical measurements to ensure that part of the wall has lost it's batter?

FMS 07-04-2011 06:42 PM

Retaining wall
My retaining wall is straight and the backfill is rock (#57) and sand witha french drain. The movement is slight but noticeable because half the wall is straight vertical and the other half still has the expected lean in toward the backfill. I have notified the contractor because I too, am concerned about any movement after only two weeks.:(

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