Timber retaining wall

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Old 08-15-16, 08:06 PM
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Timber retaining wall

Hello all!
I am brand new to this site and hoping I can get some input on a timber retaining wall I am planning to construct.

I am attempting to build a 10foot high timber retaining wall to separate my front yard from back yard

The yard slopes a lot and I want a level front half and a level back half. The front half is also where the driveway is , but cars will be parked no closer than 10 foot from where retaining wall will be.

So... My thought were to put 6x6 posts at every 4 foot or six foot buried 6 foot in ground and cemented in place. Then use 4x6's secured to the posts with carriage bolts. Towards the upper 2/3 of the wall I was also going to place a dead man every 8 foot or so to further strengthen the structure.

All wood of course would be pressure treated. Does that sound structurally strong enough??

Any feedback great fully appreciated.
 
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Old 08-16-16, 02:54 AM
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Welcome to the forums! 10' is an awfully tall retaining wall for lumber. If you use pressure treated lumber, make sure it is rated for ground contact. What we see here is the use of railroad ties, which are more substantial, but never to the tune of 10'. Where will you obtain 16' 6x6's? How do you plan on digging a 6' hole? I would not use concrete at that depth, just backfill of dirt would be sufficient. I'll let the others chime in with their opinions.
 
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Old 08-16-16, 05:44 AM
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I would NEVER consider putting so much work into a retaining wall of that size and make it out of wood. Wood rots. No matter what the treatment level is has a limited lifespan so at some point in the future the wall will have to be torn down and redone. Possible for a short wall where you want to go cheap but 10' high is a major construction.

I would use pre-cast retaining wall blocks. Not the little things sold in home centers but a proper, engineered retaining wall system. I use Keystone but there are other brands that work just as well. I find them even more DIY friendly than large timbers and if you follow the instructions you end up with a proper, engineered retaining wall that essentially has no life limit.
 
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Old 08-16-16, 07:12 AM
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What is the highest u would go with timber? I like the look of the timber and have seen quite a few photos of large residential, even commercial applications using timber. I can purchase 16' 6x6 at 84 lumber here in Charlotte area. As far as post hole digging.... An auger with 12" bit
 
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Old 08-16-16, 09:09 AM
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Most auger bits only go about 36" deep so you'll need to get a special one that can go deeper and most 3pt and rental type augers will only do about 36" so make sure the machine is also capable. Also, once the hole is deep enough to provide enough support the post becomes the limiting factor so it's pretty rare you see things sunk 6' into the ground except to get below the frost line.

I might do a wood wall a foot or two high. But higher than that the labor to install the retaining wall becomes pretty high for something with a limited lifespan. I just replaced 6 out of 8 posts on a 8 year old fence. That wasn't great life for something rated for ground contact. If you really are going to go through with it I would only use lumber treated to a higher level. It's commonly available at the coast but you can special order it.
 
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Old 08-17-16, 11:24 AM
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update

ok... so after thinking further into it,, how about this for a second option?

still need to use wood because wife says so and she says I can replace it in 15 years..

instead of doing one huge 10 foot wall, how about if I make it a tiered wall instead??

first tier at 5 foot with 8 foot posts and 3 foot in concrete, with posts at every 5 foot??? or should posts be closer/further apart?? 4x6 horizontal behind posts holding first tier together

then do 3 foot planter area and raise it 2.5 feet with 6x6's
then do another 3 foot planter and raise it 2.5 feet more with 6x6's

the two upper tiers will be done with gravel foundation and 6x6 on top of that and first 6x6 held in place with 4 foot rebar into ground at both ends and middle...and each subsequent 6x6 screwed or nailed together.

and of course will put gravel/drain behind each tier for drainage.

would that work??

thanks again!!
 
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Old 08-17-16, 11:38 AM
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still need to use wood because wife says so
Really? Can you not explain how this is a bad idea to her? Why would you want to have to re-do all this work again in short order?
 
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Old 08-17-16, 12:23 PM
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she likes the wood "rustic look" ....funny, huh!?
 
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Old 08-17-16, 12:40 PM
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Thanks for reminding me how happy I am to be divorced.
 
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Old 08-17-16, 05:43 PM
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Modern pressure treated lumber doesn't equal "rustic" in my mind.

Where are you located?

I've built a lot of micro retaining structures with 4x4-6x6 and rebar. These are steps on trails and minor retaining walls (12" high) and planters. In my area frost heave is strong enough to move most. A few whacks with a sledge gets them more or less back in shape for another season. One thing I've noticed is that rebar "pins" doe not provide much resistance to lateral movement no matter how long the rebar. The round rods just don't have enough surface area to resist lateral movement. While the bottom of the rebar a few feet underground may not move the part closer to the surface gets pushed sideways and the rebar just bends. Rebar can be used to pin a structure together but it can't be used to anchor it in place.
 
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Old 08-17-16, 07:12 PM
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A tiered wall would be better then a single 10' wall. One thing to remember, besides the wall, you will need to install deadmen. These will need to run into the ground behind the wall to help anchor it.

I saw this the other day and it came to mind: How to Build a Treated Wood Retaining Wall | The Family Handyman

Here is another: How to Build a Retaining Wall | The Family Handyman

This might also be helpful: How to Build Retaining Walls Stronger | The Family Handyman
 
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Old 08-17-16, 07:39 PM
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In my area any retaining wall over four feet high needs to be permitted and obtaining the permit generally requires engineering approval. I strongly urge you to contact the local building department, anonymously if you desire, before embarking on your project.

I also agree with the others that wood is NOT the proper material to use. A terraced retaining wall may be in order but it will take more horizontal ground to provide the proper width of the terraces. Maybe you can add a wooden facade to please your wife.

Stickshift, my sentiments exactly!
 
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Old 08-18-16, 08:34 AM
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everyone here that is responding is really against the use of wood....

is there something I am missing?? I see wood retaining walls a lot and they are all over the internet superhighway..... I must say I am quite surprised and trying to find what I am missing. trust me, I greatly appreciate all the responses and words of wisdom.... but is really it that horrible to use wood????? should I really reconsider???

I live in the charlotte, nc area where It does freeze, but not that often
 
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Old 08-18-16, 09:14 AM
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Wood will rot - sooner or later. And as mentioned earlier 10' is really too tall for a wood retaining wall. I've only seen a few tall wood retaining walls and they made me shake my head. I do have a stair stepped retaining wall made with RR ties under the power line to shore up the hill were the goat has been trying to erode it.
 
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Old 08-18-16, 09:18 AM
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You may be able to search out and find wood retaining walls on the Internet. You can find anything on the Internet. That doesn't mean that wood retaining walls are commonly built anymore or that they are the best, 2nd or 3rd best. It just means that others have done it.

Is wood that horrible? No, it's just that there are better options available. These days there are many products engineered specifically for retaining walls that offer easy installation, a reliable design and very long life.

My big beef with your plan is that you'll have a massive structure. 10' whether done with one wall or a tiered structure is going to require a lot of earth moving. To put that amount of money into something relatively temporary I would call a bad investment.
 
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Old 08-18-16, 11:28 AM
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killin me

again, thank you all for the responses, but you are killin me!!

I have my whole plan figured out and pictured in my head how it will go, but now I am on hold with a dealer in charlotte to find out how much versa lok products are!!! to be continued.......
 
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Old 08-18-16, 11:37 AM
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pictured in my head how it will go
We have it pictured in our heads as well but I think our picture is different than yours....
 
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Old 08-18-16, 11:56 AM
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cost

versa lok wall will cost me 5500 using versalok standard grey. 5.75 per block plus tax x 800 pieces... and that's not including stairs built into it

timber will cost me 2800..... with stairs

again thank you for all the input, but I gotta stick to lumber for the cost of it

start 10 foot high....... drop down to 7 foot with 3 foot retaining wall.....then 4 foot tier/plante.... drop down another 3 foot with another 4 foot long tier....then final 4 foot retaining wall

probably do bottom wall with 6x6 posts every 5 foot with 2x12s used as the wall.
do the upper two tiers with 6x6's and deadmen/bracing behind wall.

thinking structurally only... not that I may have to redo this in 10 years or so.... would that work????
 
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Old 08-18-16, 12:26 PM
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You can do whatever you desire as far as I am concerned. Have you checked with the governmental offices to see what hoops they want you to jump through? Be a shame to spend the money as well as the effort and then receive a letter from the government telling you to tear it all down.
 
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Old 08-18-16, 12:42 PM
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I would also suspect that a 10' high wall will require some type of railing.
 
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Old 08-18-16, 12:48 PM
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If you are a Fine Homebuilding subscriber they have a article on building wood retaining walls. I think you might be able to view the article as a trial member.

Keep in mind that posts in the ground can only do so much. Above several feet most of the resistance to lateral movement will come from dead men. Properly installing the dead men is key. Then, since you are planning a tiered construction keep in mind your setback for each level. Too close and the lower wall will still end up bearing much of the lateral load and pressure from the tiers above.
 
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