Retaining wall blocks?

kirkhallJune 12, 2013

I need advice on retaining wall blocks (concrete).

As some of you know, a developer is using part of my backyard temporarily while they install a water retention vault adjacent to it. As part of the deal, they will be redoing my backyard, including installing some terraces with retaining blocks to better deal with a slope in my yard.

He is giving me the choice of 2 different style of block--both of which he has used on other developments in the area. I know nothing about blocks other than, when they are installed, they must be installed "right" so they don't collapse in future years.

How do I get more information? He sent me to go look at them, and asthetically, I like one style more than the other. The first style (my favorite aestetically) is a smaller block with 3 sizes that fit together. They appear to have a ridge in their top so that they interlock to some degree. But, the blocks themselves are not heavy. And, he said they have a maximum stacking height of 3 feet. The other style is heavier, trapezoidal shape about 7" tall and maybe 15" long on the face (didn't measure, just approximating). These are what I think of as typical retaining block. I am unsure the maximum height on these, but I do know they are higher than the tumbled piza (option 1). They don't appear to interlock--just flat tops and bottoms and so I think they stay in place due to their weight.

My soil has a lot of clay. In one area, there is a significant cut in the soil which has been there for 3 years with minimal (no) collapse.

How important is it, given this type of soil, to have a stout block wall? Will the lighter weight blocks work okay, assuming a proper install? Or, will I have trouble years down the line because the clay is heavier than they are?

Thank you in advance!

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For accurate and dependable information, you need a soils engineer to evaluate and test the soils and give recommendations, based on the soils conditions, drainage pattern and height of retaining walls. This assumes you want the retaining wall(s) to last and be durable for many years.

Clay soils typically hold a lot of moisture during periods of rain (that is, the soils expand and move), and dry during extended hot and dry periods (that is, the soil contracts and shrinks). As a result retaining walls and foundations need to be designed to resist the expansion and shrinkage, as well as to accommodate the necessary drainage during rainy periods.

There's a lot more to this than the aesthetics of concrete block, which, by itself, is not designed for expansive soils.

Good luck with your project.

    Bookmark   June 12, 2013 at 6:51PM
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It will have drainage built into the system--that is one of the reasons for the remodeling of my backyard (one of the improvements being made for use of my yard space) and the reason for the retention vault for the rest of the development.

Generally speaking, the soil is always wet in this particular area--again the reason for the drainage improvements that are being made. I live in the PNW. We get a lot of constant rain with only some periods of time of "dry". But, in the 10 years I've lived in this house, I have never once watered my lawn...

    Bookmark   June 12, 2013 at 6:57PM
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Are the retaining walls for your project going to be higher than 3 feet? If so, guess that would rule out the blocks you like the best.

    Bookmark   June 12, 2013 at 7:33PM
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No. Too easy. They will likely be right at 3 feet tall.

    Bookmark   June 12, 2013 at 7:37PM
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Did he not give you the manufacturer's information on these blocks? If he didn't, I would start with that. How high a wall will this be?

Also, the maximum stacking height might be dependent on the installation method used. We used Versa-Lok blocks. With them, when you go above a certain height, you need to use a geogrid soil reinforcement.

    Bookmark   June 12, 2013 at 7:40PM
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If you have a choice on color once you've picked the best product for your application pick one that matches your soil. We are seeing a lot of soiled water staining the brick that is popular here. Proper install may also remedy this but on the high walls (much greater than 3') it looks almost unstable with so much run off and thru the brick. Red carolina clay on the grey block is messy and unsightly.

    Bookmark   June 12, 2013 at 8:52PM
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Where do I start.....

Make sure that an engineer does the design for the walls and terraces. Typically an engineer's seal is required for everything above 4' high. Large walls require a significant amount of engineering to include soils survey, geo grid (type amount, placement), block type (manufacturer), backfill and much more. Large wall block (I like cornerstone) often have a batter and require a drainage chimney behind the wall. Colors are regionally dependent since the aggregate determines the final product color and these aggregates differ from plant-to-plant.


    Bookmark   June 13, 2013 at 11:38AM
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My husband and I installed a Pisa stone wall in our back yard about 20 years ago and it has held up extremely well. It isn't three feet tall, but the system is designed in a way to allow for higher walls. (From what I remember, anything under four feet didn't require any special considerations.) From what I've gleaned from your previous postings we live in the same town. We ended up going through Mutual Materials - their Bellevue location has a sample yard where you can see installed pavers and walls to get an idea of what you may like. Also, their website can link you to spec sheets with detailed installation instructions - this can help you know what to look for when you see the construction company install your walls.

At the time we did our project, we liked the look of the pisa stone best, and after all these years we still love the way it looks. We followed manufacturers instructions faithfully, laying a solid, compacted layer of crushed, 5/8 minus gravel as our base and carefully setting the first course of stones, constantly checking our work with a level. Painfully slow work initially, but this really paid off in the long run - our wall hasn't shifted at all.

    Bookmark   June 13, 2013 at 1:57PM
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Oooh, thanks carpecattus. I had assumed you were somewhere in the SW (no particular reason though, since your name is carpecattus and not carpecactus...) Funny what little pictures one paints in their heads.

Yes, you are correct. We must be "neighbors", so to speak.

Thanks for the information about where you got yours. I'll see if I can make it there to have a look.

Diveguy and Houseofsticks,
Thank you also for your feedback. More things to pack into my bag of thoughts/observations.

    Bookmark   June 13, 2013 at 2:56PM
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You're welcome! By the way Mutual Materials also has a Redmond location, but I don't know if they have a sample yard in that location.

As for the name, I must admit I always struggle when facing the challenge of coming up with an "ID" for a website. The day I created my "name" for GardenWeb, after struggling too long with writer's block, I looked at my cat and figured carpe cattus - "seize the cat" - would have to do. Of course with the passage of time I can now think of a dozen better names! :-)

    Bookmark   June 13, 2013 at 6:07PM
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I went to Trendset today (near W'ville Costco) and they had the mutual materials stone... Now I need to talk to the developer some more. What she showed me for the RomanPisa is a full 12" deep, but what the dev had me look at was a wall with the Roman Stacked Stone.

It looks like I'll need to make sure, for my application, we get the RomanPisa and not the Roman Stacked Stone, as they have different maximum heights. Thank you for pointing me in the right direction!

    Bookmark   June 13, 2013 at 7:29PM
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