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Old 11-09-2015, 05:34 PM   #1
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Retaining wall drainage question


Hi All,
I'm getting ready to undergo a retaining wall project for a driveway extension. I've been trying to read up as much as possible and understanding failures etc etc.

First I do plan on having it designed by a certified engineer but I want to understand the drainage situation a little more.

I plan on using the interlocking blocks which require only a compacted base. My question is how the water actually flows out of the wall.

If you start with a compacted base, build the wall to surface level where you put down your drain pipe. You still theoretically have water that could exist below your drain pipe. Down to your first course or base.

This is an example : https://i.ytimg.com/vi/eyXw9-1ggos/hqdefault.jpg

So my question... is the drain pipe primary purpose to remove water from behind the EXPOSED wall but not the foundation portion of the wall? Since the drain pipe is perforated on all sides the water will have to be higher than the first course of blocks in order for it to begin to flow. Am I making any sense?
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Old 11-09-2015, 06:15 PM   #2
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Ayuh,.... How high is the wall gonna be,..??

What's above the wall,..??

It's best to divert any, 'n all the water as far as possible before it gets to the wall, than to deal with it after it's there at the top,....

I put the tile at the bottom back of the lowest point of the excavation of the native soils,....
Swales at grade at the top to divert surface water,...
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Old 11-09-2015, 06:27 PM   #3
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Quote:
Originally Posted by Bondo View Post
Ayuh,.... How high is the wall gonna be,..??

What's above the wall,..??

It's best to divert any, 'n all the water as far as possible before it gets to the wall, than to deal with it after it's there at the top,....

I put the tile at the bottom back of the lowest point of the excavation of the native soils,....
Swales at grade at the top to divert surface water,...
The highest point of the wall will be approximately 8 feet (to floor). I'm debating on extending for a small wall or fence as required. But the height will only last for approximately 5 feet and then step down. My thought right now is to have it gravel until the following year and then have it paved. Currently the driveway is graded to support a one lane drive way and a small turn around area. We plan on making it three spaces wide ~36 feet so essentially the graded area will be part of the excavation and backfill.

I also need to determine whether or not I should cut into the graded hill and step up the wall or just cut and level the ground which will extend the length of the wall height.
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Old 11-09-2015, 06:31 PM   #4
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Retaining wall drainage question-drive.jpg
This is the area I plan on building up. In the rear you can see the mound of the incomplete circle driveway.
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Old 11-09-2015, 07:22 PM   #5
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An 8 foot high concrete segmental block retaining wall requires select backfill behind the wall, plus reinforcing strips to stabilize the fill behind the wall. The select fill (sand and gravel) must be sufficiently permeable that any water that would normally build up behind the wall drains downward to the drain tile, which carries the groundwater safely away to a lower area. Your engineer will design all of this for you. An eight foot high wall must be built carefully and correctly, the penalty for poor design or inferior construction could be a serious failure.
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Old 11-09-2015, 08:05 PM   #6
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An 8 foot wall requires an engineers stamp in any type of regulatory jurisdiction worth a crap. That will ensure that you do not even need to ask this question.
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Old 11-09-2015, 09:46 PM   #7
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Thanks Daniel! @TSC ar I like to learn as much as possible and ask the right questions when contacting work. Just trying to do my do diligence here.

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Old 11-10-2015, 06:24 AM   #8
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Quote:
The highest point of the wall will be approximately 8 feet (to floor).
Ayuh,.... Do you own the land on the low side for say 8' to 16' out from where ya want the wall,..??..??

If so,....
Forget 'bout the wall, 'n bring in move fill,....
A 1 on 1' slope will hold forever, without a wall,....
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Old 11-10-2015, 03:01 PM   #9
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Quote:
Originally Posted by JamesCE View Post
Hi All,
I'm getting ready to undergo a retaining wall project for a driveway extension. I've been trying to read up as much as possible and understanding failures etc etc.

First I do plan on having it designed by a certified engineer but I want to understand the drainage situation a little more.

I plan on using the interlocking blocks which require only a compacted base. My question is how the water actually flows out of the wall.

If you start with a compacted base, build the wall to surface level where you put down your drain pipe. You still theoretically have water that could exist below your drain pipe. Down to your first course or base.

This is an example : https://i.ytimg.com/vi/eyXw9-1ggos/hqdefault.jpg

So my question... is the drain pipe primary purpose to remove water from behind the EXPOSED wall but not the foundation portion of the wall? Since the drain pipe is perforated on all sides the water will have to be higher than the first course of blocks in order for it to begin to flow. Am I making any sense?

I understand what you're asking. We've never set a draintile below the block to drain the gravel footing, and I've never seen a reason to if you deal with the water above. This attached image is how we have always installed the pipe, with the bottom ABOVE the grade on the front side of the wall. We usually fill the back portion up an inch or two higher than grade, sloped to the front, and tammp in in first to divert the water towards the front of the wall as quickly as possible.

https://www.google.com/search?q=vers...NkHCwR3B38M%3A
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Old 11-10-2015, 07:14 PM   #10
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Quote:
Originally Posted by Bondo View Post
Ayuh,.... Do you own the land on the low side for say 8' to 16' out from where ya want the wall,..??..??

If so,....
Forget 'bout the wall, 'n bring in move fill,....
A 1 on 1' slope will hold forever, without a wall,....
hahaha sooooo I did have a contractor come out and recommend something similar.
He wants to do gabion stone reinforcement and backfill. My only concern is that I want the wall to extend to the last portion of the green covering in the picture. The remaining 10 feet would/could be used for vehicular traffic to the rear of my property. So I definitely own 100+ feet in all directions.

Honestly I've been debating this back and forth. One part of me says just do the backfill since I need it anyway for the wall and see how it works out. Then get the wall if I reallllly want the space.
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Old 11-10-2015, 07:57 PM   #11
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Sounds like you are not on a budget. If you don't want an earth slope, the retaining wall will look a heck of a lot better than a gabion basket.
What do you have going on that you need that much room
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Old 11-11-2015, 08:06 AM   #12
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Budget is always a consideration. See this Contractor said it would not be in Basket. The driveway is over 1000ft and no area to really turn around so when we get deliveries they can get stuck. I had to pull UPS out the last time.

Maybe I can look into soil stabilization options for mounds.

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Old 11-11-2015, 01:14 PM   #13
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Quote:
See this Contractor said it would not be in Basket.
Ayuh,.... Fill, cover, 'n grade is a once, 'n done thing,... Forever,....

Walls, at some point will need fixin',....

Fill, 'n cover, you can replant trees, or just let mother nature take it back,....
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Old 11-11-2015, 03:50 PM   #14
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You are a heck of a nice guy to go to that extreme for delivery guys. When conditions were too soft for our UPS drivers to turn around, they would just back down the driveway (900') I even told some drivers they could turn around in our yard, but they wanted to back out, for whatever reason
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Old 11-11-2015, 06:11 PM   #15
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I let them turn around in the area to the left but it's too soft when it rains... I'll get it fixed up soon lol

Time to look for backfill

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