Retaining Wall Help

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Old 07-07-11, 10:34 AM
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Retaining Wall Help

I am gathering supplies for the retaining wall I am putting in. Is it okay to use 3/4" red rock as backfill? I've also heard crushed concrete is a cheap option. I can only find that in inch and a half.

What type of chisel/saw should I use to break the blocks when needed? I am using the keystone blocks (8" h x 12" d x 18" l).

Also, is it absolutely necessary for me to run a drainage pipe? I have heard different opinions on this. I also see some very large walls without them and oher smaller walls with them. If I use one, do I notch out a block and run it through the wall itself? Thanks for the help!
 
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Old 07-07-11, 01:55 PM
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First, a question. If there wasn't an existing wall, why is one needed now?
Any gravel or stone is good for backfill & drainage. The water has to have a place to go. It doesn't have to be a pipe. You can make weep holes in the block itself.
If the block is too big for a wet saw, rent a partner saw.
 
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Old 07-07-11, 02:51 PM
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For a Keystone wall, you do not need any weep holes because of the open joints since they are never mortared.

If you have any outside square corners, you may need a saw for cutting special lemgths. Usually, a hammer and mason's chisel work well because the block face is split and may be curved. It takes a try or two and it is easy to do. Score lightly with a few taps and your ear will tell you when it is aplitting.

Those block are brutes and do not get up and run away from you.

Dick
 
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Old 07-07-11, 03:05 PM
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I saw cut Keystone retaining blocks. I don't have Dick's magic touch with a chisel and I've had more than a few crack where I did not want. I use a diamond blade in a regular circular saw. It's extremely dusty but it works. Make sure you stand up wind and a good respirator is not a bad idea.

I always wear steel toed shoes when working with the retaining blocks. They are so heavy that if one slips out of your hands...

I generally do not put a drainage pipe behind. The gravel & landscape fabric on the back side of the wall lets any water easily find it's way through.

Make sure you get a good, level compacted base prepared before you start setting the blocks and make sure the first row is level & straight (or whatever curve you want). Whatever time you spend insuring that the first layer is perfect gets paid back ten fold when you can quickly zip through the upper layers. If you are sloppy with the first row you might end up fighting it the whole way.
 
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Old 07-07-11, 03:17 PM
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There was an existing concrete block wall. It bowed and needed replaced.

Do you think it is necessary to offset the blocks with the different pin settings or should i go straight up and down? It will stand approx 5 ft tall. I am concerned that offsetting the blocks will make my corner more difficult and make the other side running by my stairs look odd (wall will be in am L shape).

About 6" of gravel base leveled out and compacted well should do the trick right? I've also been told not to over compact the backfill as it will stress the wall.

Lasrly, I am only planning on putting fabric over the top of my backfill, approx 4 to 6 inches from the top of the wall. Is this appropriate and do I need fabric between the rest of the backfill/base and the dirt behind it?

Thanks again!
 
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Old 07-07-11, 03:27 PM
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If the existing wall is bowed, what caused it & why wouldn't it happen again, especially if keystone blocks don't use mortar? You have to rethink your project.
 
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Old 07-07-11, 03:35 PM
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Rethinking is not necessary... The old wall had no backfill, just back by solid dirt/clay. I also believe that they had the slope of the lawn above wrong as the top of the wall was washing away. I'm not sure what rethinking the project would accomplish.
 
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Old 07-07-11, 03:43 PM
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I have seen 40' high segmental retaining walls around the world on freeways and all builtt with no mortar and absolutely no concrete footing.

Cutting the batter or slope will result is a weaker wall, which could be a problem since your are 5' high.

Square corners can be a big problem (detail-wise), but inside or outside curved corners are easy and very strong. Many codes us 4' or 5' as the dividing line between a gravity wall and an engineered wall that can be many time higher.

The existing wall was probably just a typical old plain block wall, possibly on a footing not wide enough to stop tilting and spread the load out.

Our local municipality has standard detail plates for municipal crews (regrading widening streets and sidewalks etc.) and for contractors and home owners. Each of the 4 major international systems (Allan, Anchor, Keystone and Versalok) have great installation tips and drawings on their extensive web sites. The system is well documented and proven and that is why it is most common system on non-building (civil, landscaping, etc.) applications.

Dick
 
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Old 07-07-11, 04:00 PM
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So the 3/4" red rock is okay for base and backfill? And landscape fabric on top layer will cut it?
 
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Old 07-07-11, 04:27 PM
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I have no idea what "red rock" really is.

For a base, it muct be compacted and many "clean" materials(no fines) cannot be compacted. A clean coarse aggregate can eventually be clogged by fines washing in from the surrounding soil

Dick
 
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Old 07-07-11, 04:57 PM
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I assume it is quartzite, not sure of spelling. What type of material would you suggest for base and backfill?
 
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Old 07-07-11, 05:19 PM
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The red gravel will work for behind the wall, but not for the base. I used QP (quarry process) for my wall. It was crushed stone ranging in size from stone dust up to 1 1/2". I believe crusher run is the same thing by a different name. Where are buying your blocks? They don't supply the base material? You should also be able to find a place that sells 3/4" blue stone instead of the red. It will be cheaper to buy.
 
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Old 07-07-11, 07:20 PM
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Okay, so if I'm understanding this right, I am better off using some sort of base material with fine pieces and a mix of larger pieces ranging from 3/4 to 1.5"?

The red rock is what the local place has. $20/ton for that. Crushed concrete 3/4 is $14/ton. Material is scarce right now. A lot was used up by others combatting flooding in the area.
 
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Old 07-08-11, 04:42 AM
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$20 a ton sounds cheap enough. I think I pay $25 for the crushed blue. I forget what the red cost me, but I think it may have been higher.
 
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Old 07-12-11, 04:31 PM
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Yes about the wall

I've used similar red gravel behind wall areas, glad someone confirmed it aswell
 
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