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Landscape Design

Need help building a retaining wall

7 years ago

Hi all this is my first post so I hope I can get some input. I have decided to build a retaining wall using pressure treated wood. The original plan was to build three walls and have 2 separate levels. Now after building one wall I want to just go higher and build 1 more wall a little taller vs 2. So creating 1 larger level. Im using 4x4 posts every 4 feet with 2x8's behind. The soil is full of rocks from the 2 inches to 5 or so inches. I live in San Diego so the weather isnt too intense to say the least.

My question is when does a wood wall need to have deadmen? And if I need them how exactly would I build them on this design. My idea is add another 2x6 onto this wall and build about the same size wall up top. The walls would be right around 35.5" but the dirt would be lower leaving a 3 or 4 inch lip so dirt doesnt overflow.

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Comments (5)

yportdesign
7 years ago
A wall needs deadmen when the mechanism to overcome failure is mass and the mass of the wall needs extra ballast to do so. Your wall is relying on nothing but vertical posts at this point. It will fail by leaning over assuming that it is well anchored. If it is not well anchored it could fail from the bottom rotating out and upward.

A deadman is used to combine the mass of the soil that it binds to the wall to overcome the force on the wall. Many people believe that it attached the wall to the slope, but that is not correct.

A method to make this type of wall design work that is often done with vertical sea walls is the use of helical anchors.

Have you ever seen a retaining wall like yours?
jeffboyardeee thanked yportdesign
jeffboyardeee
Original Author
7 years ago
My neighbor has done similar, creating terraced garden beds and I have seen some around town. I never knew if the shorter walls had any anchors or not. I explained what and how I was building the wall at the local lumberyard and they said as long as I dont go higher than 3 or so feet I should be fine. The posts are as deep as they are high.
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I am surprised that you did not think of the following. You need to build a temporary dam at the top edge of the wall to hold back the clay. This is done by pegging lengths of board along the wall. Boards can be found in construction site dumpsters or your local newspaper probably has wooden pallets for nothing that you can take apart. This is your first step. You seem to think that it is possible to till the clay and reduce the slope. I am not certain this is a wise move as you will have disturbed clay which will quickly erode. Perhaps it is best to leave the slope as it is presently and lay landscape erosion netting on the surface, mulch on top of this and plant. The netting can be ordered from any landscape nursery. I would urge you to pay for a consultation with the owner of a landscape nursery to advise you on this situation. It will save you from making costly mistakes and allow you to address the situation correctly. Then you will understand 'terracing' which may be the prefered solution. Either way, netting or terracing, it is important to stabilize the slope before planting. Most fast growing ground covers in Zone 7 are very invasive and after a few years you will hate them. Better to consult with an expert who can suggest shrubs and native plants that will grow in clay and afford you an attractive view. There is a solution to your problem, but as a non-gardener you need expert direction for a tricky situation. Hopefully you will set out to find the help you need before making some serios mistakes.
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Except for the dog issue, I'm confused about what you're trying to do with fences. If you must fence the property line, which it as top of berm, I presume you would eliminate fence close to retaining wall (so as not to have a strip of land sequestered in between two fences.) It would be vastly easier to understand if you'd take a site plan (I'm sure you have one since the house is currently being built) and mark out your intentions, and submit a photo. Hopefully it will explain what/how you mean about running a fence "half way." In regards to the issue about the dog or children jumping off the retaining wall. I can't really believe either wouldn't be able to learn their capabilities almost instantly. The wall doesn't look high enough to be a real danger and won't there be unpaved areas at its lower side? Doesn't seem like a problem. When I was a child we would think this wall a nice toy. Plantings could easily limit access.
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PRO
Yardvaark
7 years ago
When someone in a retail outlet says "you should be fine," they are not going to be accountable for that statement. My "gut" reaction to your picture is that this wall will not last. Much of 2x lumber is treated for exposure to weather, not for ground contact ... so check that. You might think of the slope as a slow moving glacier. The 2x are probably going to bulge and the posts probably won't keep the wall from tipping. It looks like a temporary solution.
cakbu z9 CA
7 years ago
Some years ago I had made a similar retaining wall; mine was made using 6X6 treated posts and 2X12 redwood walls. The posts were set in a LOT of concrete. Wall was about 3' high. Drainrock was put between the wall and the hard-packed soil. The wall began to fail after 7-8 years. Posts leaned and became worse year-by-year. I sold the property and the new owners will have to deal with the mess.
John F
last year
Any update on the wall? Did it withstand time?

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