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Discussion Starter · #1 ·
We have these retaining walls that are beginning to bow out and lean a bit on our home we just purchased a few months ago. I did a little exploratory digging and I noticed that drainage appeared very poor. Lots of moisture in the soil and no gravel fill behind or under the existing wall. I suspect this wall is at least 25 - 35 years old. Most of the ties are rotten or decaying on the fill side. They are fixed simply by 1/2 and ¾ rebar driven a few feet into the ground. They still hold pretty well and are a bit of a bear tearing up but doable by prying the tie up enough to get the recip saw in there and cut the rebar.
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The total height of the terraces is about 68”. I want to use cinder block CMU’s for the new wall so we may add a stone veneer. Since the finished wall will be roughly 10”-12” thick, I am opting to reduce the number of terrace walls by one so there will only be 3 walls instead of 4. Otherwise, the usable terrace space will be a bit small. It will also make it easier to dig in the footings etc.

My plan is to build the wall with 8x8x16 cinder block, core filled with ½ rebar every other core.
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Wall Strength
I am largely unsure how to determine what will be good enough short of hiring an engineer. I see all different types of footings and sizes and the requirements of course depend highly on the type of substrate. I’m not very familiar with soil types per-se, but I would describe the soul as primarily clay and granitic sand. Holds shape and forms well, hard as a rock when dry. The photo shows the first foot or so. Deeper than that, there is much less gravel and more clay content.
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Since each terrace wall will be only about 2’ above grade a 10”x8” footing feels like it will be more than enough provided the drainage problem is solved well.

I want to build this wall to last but I also want to avoid spending time, money, and space installing footers that are needlessly large.

The quick drawing details the first wall. Sorry, no annotations. Also absent is the drainage systems, masonry detail, etc. The bottom dotted line is the frost line. Vertical dotted line is where the slab ends.
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Drainage
I plan to fill each terrace with a drain and gravel similar to what is shown here https://jensen-architects.com/case_...ads/screen-shot-2013-08-21-at-11.42.04-am.png The wall abuts a slab and pool so I’ll add a similar drain at the base in front of the wall to catch any overflow.

So far, it seems my only hang-up right now is deciding on footing size, depth, and placement. eg footer heel, toe, thickness size. Should the entire footing sit below the frost line? The existing ties have no bury and the only thing holding them is the 2-4 3/4" rebar driven ~2' into the soil. Any advice and recommendations would be most helpful!

Thanks!
 

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Have you checked with your city to see if a permit is required? If you were just rebuilding it like-for-like you might get by calling it maintenance, but what you are doing probably falls under new work. And a permit for a retaining wall that high might require an engineer.
 

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Discussion Starter · #3 ·
Have you checked with your city to see if a permit is required? If you were just rebuilding it like-for-like you might get by calling it maintenance, but what you are doing probably falls under new work. And a permit for a retaining wall that high might require an engineer.
I am checking on the building regulations.

The state building code says that you need a permit for anything over 6' from the bottom of the footing to the top of the wall. There are a few other city regs that restrict height based on wall placement (facing a residence etc). One of my neighbors used to be pretty high up in the State Regulation and Licensing Dept. and he mentioned in passing one day that the way around the 6' limitation was to terrace the wall. I do want to get more of a firm answer on this eg does distance between walls matter, etc.

Our wall would be under 6', even if done as a single segment, but not down to the bottom of the footer of course.

To be honest, I'm not terribly concerned with the engineering part of things, after all, staked in sleepers held up for 30 years, but I do want to stay above board and do things reasonably well.

I should also note that my rendering may depict a full concrete slap on top. This is not the case. About 2/3 is astroturf on dirt and the other 1/3 at the far corner by the existing block wall is slab.
 

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Discussion Starter · #4 ·
Did some more reading of the city regs and it looks like my plan does fall under the purview of permitting.

Per the city, a retaining wall up to 24" in height may be built without a permit and any retaining wall over that must be permitted. Additionally, any retaining wall retaining more than 24" of material must have the approval of a structural engineer. Additionally, terraced sections are not considered independent unless the distance between walls must is at least twice the height of the upper wall. So it looks like I will not only need to get a permit, but I'll also need to get a structural engineers stamp since my plan is at least 8" short of this and I don't have enough space to make it work otherwise so I'll need to take surcharge loads into account. It will at least be interesting to see how my proposed plan stands up on the engineers desk.
 
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