Tell me what I'm doing wrong building my first retaining wall

5 years ago

I'm tackling a huge project to build a 4ft retaining wall 150ft long in front of a hill in my yard.

The wall will remain 4ft along the 150ft distance. I am not making the wall higher or lower to accommodate the height of the hill behind it. Instead, I am going to slope the hill down into the back of the wall. I'm using g-force from techo bloc, which are 80lb retaining wall blocks.

I've done a ton of research and am not cutting corners. For context, I've done small patios and decorative walls before, but never a retaining wall of this size. I've rented machines, I am using a laser transit, I put in the proper compacted base with geotextile fabric, will be running fabric along the entire backside of the hill, using a perforated drain pipe for drainage, backfilling with 3ft x 3ft of clean stone up the wall, and will be using geogrid every two layers of wall.

For context, here is where I am at so far: https://i.imgur.com/8lZp5JT.jpg (not pictured -- fabric will be running up to the top of the hill to prevent soil from mixing with my clean stone backfill)

Now it may be hard to notice but in the picture you can see that the land slopes away from the house in two directions. On the side of the house, it is sloping down towards the driveway entrance, and from the back of the house it is sloping down towards the bilco door.

This means that in the corner of my trench I'm down about 2 feet, and at either end I'm barely about 8 inches below grade to get 1 full block buried.

https://i.imgur.com/Uf9MwGr.jpg

https://i.imgur.com/ApKCBZJ.jpg

I did not want to step up the trench, as it is a considerable amount more work so I just made the pad level all the way around but of course at one point I'm 2 feet below grade and at either end I'm 8 inches below grade. Is there any reason I cannot just bury 2 full blocks below grade? Similar to this diagram I drew?

Final wall: https://i.imgur.com/IX4FYO3.jpg

Grade: https://i.imgur.com/loGNMRG.jpg

This is the only thing concerning me at this point before I begin laying blocks. I saw a video about stepping up your trench and it did not occur to me to do it this way until now, though it looks like 2x the amount of work instead of just burying more blocks below grade. Of course it is not like I am burying 5 blocks below grade, so not sure if this matters or not:https://www.youtube.com/watch?v=TtIXUMTcB24

Any insight/tips would be appreciated.

Featured Answer

PRO

Yardvaark

5 years ago

I believe you with the measurements. It's just that it doesn't show up well in the photo so is misleading until you clarify twice :-) And I understand how you're going to remove more from where the grade is higher toward the corner of the wall. And all of your drainage from behind wall sounds great.

"Yes" to having swale above wall to direct water from spilling over it. (But I know in real life that some may go over the top of wall.) Nevertheless, the design should be directing water to run toward ends of wall since you want it to go around the sides of house. This would happen both above and below the wall. We haven't seen the slope so don't know what you're working with (against?). Keep in mind that you DON'T want water rushing down the hill, collecting directly at the back of the wall, and then running left or right to get to the wall ends. Such a volume of water, running fast, would wash out material from the back of the wall. Chances are good that you don't have a lot of room for creating a swale. You might need a flume instead.

Keep in mind your wall should turn 90* back into the slope at its ends. This part of what it takes is to prevent washing out from behind the wall.

There are a lot of details for this project and site that we are unaware of, so ask where things are not clear.

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Comments (12)

Judy Mishkin
5 years ago
"I've done a ton of research and am not cutting corners."

I think you cut a major corner when you didnt hire someone who does this frequently, but I'm guessing you are far far braver than I am!
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gardengal48 (PNW Z8/9)
5 years ago
Have you researched whether or not this is even allowable as a DIY project? In many areas, there is a limit to the height of a block retaining wall without it being engineered and permitted and typically the cut-off point is 3'.

I'd also be interested in the type of block/CMU you are using and how you intend to anchor it.

Also, few are inclined to have to manually link to any photos on an outside source. It will make a far clearer and more understandable presentation if you embed the photos directly into your post.
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indigoheaven
5 years ago
Have you checked your local codes yet? you may need to get a permit and have an inspector come out.
0
chiflipper
5 years ago
Dear Brave (or insane) Dude, get an engineer on site now. Spend the money for a Pro plan...with specs. You are undertaking a huge job and materials are expensive. Better to have the "seal of approval" now rather than a disaster later. Just sayin.
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Yardvaark
5 years ago
One thing I can't tell from the picture, but it doesn't look as if you have pitch (or much pitch) away from the house...?? If it exists, does it continue far enough away (about 10')? Even if you use the wall to redirect water coming off of the slope, the water that falls below the wall must be directed away as well. If this is not adequately taken care of, your wall might be set a little high.

Given that the slope descends as distance away from the corner increases, it seems your retaining wall, without stepping down, will become a freestanding wall as it approaches both ends. This strikes me as it's going to be an odd look. Is this what you're going for? I would think you'd want to incorporate step-downs, keeping them minimal, and with more or less uniform distances between them. It might help if you explain WHY you are going for a uniform height across the span.
gmireski
Original Author
5 years ago
@Yardvaark(9A) it does slightly pitch away from the house and it all pitches down towards the bilco door area (in that first picture). We don't get water collecting near the house foundation.

I'll be doing a patio in this area after the wall is done, all water will drain towards the bilco door as the land there slopes all the way down towards the woods. I want the wall to be 4ft all the way around to keep it uniform, I'm not a fan of the step up/down style, especially within the patio area that I'll have.

The hill behind the wall is 4ft at the lowest point at the end of the wall on each side, so the wall will not be freestanding in any area (it may be hard in the pictures to tell the height of the hill behind the wall).
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PRO
Yardvaark
5 years ago
Looking to the right in your picture (Bilco direction) it seems there is a radical difference in grade at back of wall between that end and at the corner near where the camera is. If it's 4' differential there, what must it be at the corner?

I get that you want simplicity & clean lines by not stepping down. Too much of it done wrong can look very bad. But done right, it's not just OK, it can add positive interest. (I'm speaking in general. No idea about your overall plans & what fits.)

To get back to your question about burying blocks. I'm not familiar with the exact product you're using, but just the general concept. I see no problem with burying additional blocks. The problem would come if you're not burying enough. (Some people would want to set the wall right on grade thinking it's going to stay. Haha.)

Not sure what your length of time observing rain being no problem has been. But I'd definitely be grading for the most massive, ongoing rainstorm you can conceive of. These things come and if there isn't enough space within the swale (which in this case will be part patio) water starts going where it shouldn't. It's just a heads up. (It sounds like you're trying to be very careful.)
tatts
5 years ago
Post real pictures in here, like everyone else.

Don't make people who are volunteering their time for free go on some wild goose following links that may or may not be safe.
gmireski
Original Author
5 years ago
@Yardvaark(9A) -- its right at about 3'9" - 4ft across from bilco door, and it the highest corner right around 7'9"-8ft. We'll be sloping the hill down into the back of the wall. Beneath the wall we'll have 4in perforated pipe, along with 3 feetx3feet of 3/4 washed clean stone, with geotextile on top, then 1ft of soil to the top of the wall.

I am also worried about the rain off the hill behind the wall, and considered doing a second drain pipe closer to the top of the wall to catch the initial build up before the pipe at the bottom did, but was told by several people it was not necessary. Should I put in a swale at the top of the hill to avoid large amounts of rain coming into the back of the wall at once with a heavy storm?
0
gmireski
Original Author
5 years ago
@tatts -- sorry, I tried uploading here however it kept giving me errors, that is why I opted for imgur, which is an image hosting service.
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Denita
5 years ago
You can post in the comment section here
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Tell me what I'm doing wrong building my first retaining wall

Yardvaark

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Judy Mishkin

gardengal48 (PNW Z8/9)

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Tell me what I'm doing wrong building my first retaining wall

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