Replies

1. 
   DanH | May 15, 2012 07:16pm | #1

   The retaining wall blocks are easy to use and require less site prep than the other options, and they are decent looking without facing.  Three feet is just a hair high for them, though, so it would take some care in planning, and you'd want to use the larger size blocks.

   Three feet is also high for your other options, though -- you'd need to build a tilt into them to resist the soil pressure.

   You might want to double-check what height you can go without permit/inspection -- it think 3 feet is "safe", but better to be sure.

2. 
   IdahoDon | May 15, 2012 10:02pm | #2

   You can contact Basalite or a company like it that sells retaining blocks and pre-engineered retaining wall systems for various hights - they can tell you requirements for the system to hold up and local regulatory requirements to meet code.   The new systems use a horizontal mesh to lock the soil together that is tied into the blocks with rebar at a specified number of courses - retaining walls built like this can be quite high.  

   For looks and long term performance it's probably hard to beat an engineered stacked block wall. 

3. 
   VaTom | May 19, 2012 07:38am | #3

   Concrete is always my choice.  If you use forms for a thicker wall, you have room inside the form to place whatever you need to give your wall the appearance you want.  Here's a stock engineering drawing for a 4' wall.  You can put the footing on either side of the wall.

   
1. 
   DanH | May 19, 2012 07:45am | #4

   I wonder how vertical that wall will be in 20 years.  (Of course, it depends on location -- might survive better in the South, with non-expansive soils.)

1. 
   VaTom | May 20, 2012 08:32am | #5

   Dan, if you're asking about expansive clays like bentonite, that needs to be addressed.  My experience with concrete retaining walls goes back over 40 years, including the parts of Denver where bentonite can collapse a basement.  This is a separate issue.  One which must be considered in the south also, anywhere expansive clay soils exist. 

   If you're asking about frost heave, there's a reason why foundations have different depths required.  Why I mentioned that the footer could alternatively be placed under the fill, which I usually prefer.  

   The question was what type of wall to build.  Reinforced concrete works extremely well and I've not found a cheaper way to accomplish the task, long term.  Easy enough to make it look like almost anything.  As you go higher, you just need appropriately more wall and footer.  I've got 15' of fill behind some of my concrete retaining walls.  That's a BIG footer with considerably more rebar, but still cheap overall.

   That wall will last as long as the concrete.  

   Last fall I visited my old place in Denver, with a similar short concrete retaining wall looking like it did 30 years ago.  It was great to see what the current owner had done with that 1911 commercial building.  He was excited to meet me, responsible for some major changes I'd made.  The dove-tailed hickory stairs to the roof really got his attention.  The retaining wall he never much noticed, it just sat there, doing what it was supposed to do.  I also drove by the 11 acres of apartments I'd helped build the concrete foundations for when I was in school.  The engineer apparently got the bentonite preparation correct.  IIRC, they were planning for 6" of soil expansion.

   Yup, I'm a concrete fan.  Haven't found anything better for walls.  That's why my house is concrete and I consult on other concrete houses.  One was buried in France earlier this year, which I'll visit in August on part of a concrete house tour, mostly thinshell.  Friday I drove a deck guy by a 4' retaining wall I cast many years ago.  From 10' away it looks like a delapidated board fence, with rotten lumber, 75' long with a curve.  Just what the client wanted and didn't mind paying for the colored concrete.  Got the wheels turning in the deck guy's head, the lifespan and flexibility of reinforced concrete.

4. 
   annaconcho | Jun 19, 2012 02:16am | #6

   short retaining wall

   I love dry-stack.  If done properly, it falls back into the slope (batter) lessening the chance of tipping over.  If failure does occur on a portion, dismantling and reassembly is relatively easy.

   In the Austin area, we have wet-sawn limestone available in a variety of sizes: 4inch by 4 inch up to 3foot by 3foot.  Code requires a permit and engineering on walls over 4'.

   I dig deep enough that 2/3 of the lowest rock will eventually be below grade, compact the soil, install a filter fabric base extending up the back of the wall, install and compact 1-6 inches of decomposed granite depending upon the eventual height of the wall. Stack the rocks one on two and two on one with a nice batter back into the slope.  Do not install straight up vertically.  If it is battered into the slope, it is leaning back into the slope.  For failure to occur, it needs to be pushed up to vertical then over.  You can backfill with soil on a low wall and crushed rock on a larger wall.  One problem with limestone, is that it is porous, so with freeze thaw cycle, it flakes off the front edge of the wall.  Size your rocks appropriatly.  Flexible caulk type specialty glue can be used on the top course to reduce kids knocking a rock off the top of the wall.  I would not use glue on the other courses, you want the wall to breath with the earth!

   As an aside, a curved wall should be more stable than a straight wall, all things being equal.

   CMU walls are weak and ugly. (IMO)

1. 
   DanH | Jun 19, 2012 06:59am | #7

   Yep, dry stack is the way to go.  Takes time and a modicum of care, but plenty of appearance options (lots of nice precast units to choose from) and very robust.  And it looks better than poured concrete.

1. 
   Tom Richards | Jun 19, 2012 11:19pm | #8

   cheap material from salvaged concrete

   I have experimented with salvaged concrete.  I look for consistent 4" pieces from a slab that was poured over leveled sand.  I take a diamond wheel to the pieces to square up the ends so they'll lay together. Score top and bottom and then break with a broad chisel. I have tried using soft mortar made out of sand and garden lime.  I rake the joints 1/2" deep.  Follow all the rules for footings, batter and drainage.  Have only started working with this method and haven't had the opportunituy to do much, but I like the way it looks.  You could form up and pour the top course.  I'd score it every 30" or so to allow it to break nice.

5. 
   maveerdil | Jun 20, 2012 12:54am | #9

   Choosing the most appropriate material is the first decision you need to make when starting a retaining-wall project. Before you begin building a wall, you also need to consider the elevations of the new finished grades, the appropriate base and how to backfill properly.

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