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Old 03-26-2012, 10:08 AM   #1
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Retaining Wall Geogrid + landscape fabric?


Good Morning All,

The sun is out, Connecticut is getting warmer, and the plans are just about set to go with my MAJOR wall project. I plan on starting a new forum once I break ground so you all can see my before and after and let me know how I am screwing it up.

I searched around this forum and found this great thread (Block Retaining Wall - Best Practices Question)
that has diagrams for how I should be doing everything. I have four questions that I just don't see answered yet.

1. My wall is going to peak @ about six feet, so I am definitely going to be using geogrid on every other course. How far back should I bring the geogrid? Considering the amount of digging I will be doing, I don't want to overdo it, but I want to do it right. Also, do I just let it sit or do I apply tension to the end in the dirt somehow (like a rock).

2. I want to use landscape fabric also, to keep the dirt from getting into my gravel drainage area, but I can't envision how that would work with the geogrid. Do I just do strips in between the geogrid layers? It doesn't seem like that would stay in place...

3. The wall I am taking down is a poorly constructed rubble wall. Lots of big rocks. Would it be a bad idea to bury some of those rocks in the dirt part of my wall (blocks-gravel-dirt) to avoid trying to get rid of them else where? I would make sure they are at least 3 feet underground. I also thought the big rocks would be a good way to keep the geogrid in place, if possible.

4. Should I tamp the dirt AND the gravel after each course to minimize subsequent settlement?

I plan on asking the block and gravel supplier these same questions, but you guys are always on the ball with this stuff. Thanks in advance!!

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Old 03-26-2012, 10:59 AM   #2
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Retaining Wall Geogrid + landscape fabric?


The exact design of a segmental block wall is always dictated by the manufacturer of the block. This includes critical details such as how far back the fabric has to go, the exact specification for the fill material, what type of footing (if any) you need, how is drainage to be handled, capstone installation, batter of the wall, and a myriad of other details. You can certainly get opinions and information from this forum, however most of it will not be applicable to YOUR wall because it will be for a different block manufacturer.

For example, I have a complete design manual for Versalok, however their details are different than for Allen Block, or Keystone. They use different types of grid reinforcing, the block sizes are typically different, etc. So here is my suggestion. Get the manufacturer's design manual, they are often available on line. Follow the manual religiously. If there is something you do not understand, talk to the manufacturer. Resist the temptation to get opinions from your neighbor, this forum, etc., until you have thoroughly and completely understood how the manufacturer believes you should build using their product. If you still do not understand what they are saying, and they either cannot or will not explain how to do it their way, then it might be a good time to get outside opinions. Be prepared to get very confused if you do solicit outside opinions on design issues, since there are going to be many opinions, sometimes backed up by limited knowledge and experience.

Installation techniques are a different matter, for example what is the best tool to excavate type questions. The block manufacturer is not going to tell you gritty details about installation, for example how to insure your wall is level, how to safely lift a heavy block. Those types of questions are great for a forum like this. Your first four questions are almost certainly going to be answered specifically in the design guidelines for the specific block you use, so I would start there.

By the way, I recommend using block manufactured by a well known manufacturer who will furnish you with full design guides. There are knock off block manufacturers who cannot or will not furnish design guides, and cannot or will not answer questions. In my opinion, the cost savings for that type of installation is not worth it.

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Old 03-26-2012, 02:56 PM   #3
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Retaining Wall Geogrid + landscape fabric?


Thanks for the detailed and thoughtful reply. I called my local dealer of blocks, and they recommended versalok, and I am also going to meet with them on Thursday, will report back at that time. I also found versalok university (their online help guide), really helpful stuff. Thanks for the the thoughtful detailed answer. Like always, I didn't get the answer I was looking for, but I got something better. Teach a man to fish....


One question I feel someone could explain. IF my manufacturer or dealer recommends me doing so, (will follow versalok's advice at that time), how does the intersection of the geogrid and the permeable landscape fabric work?

See this picture for reference. It calls the landscape fabric "filter cloth" in the image.
http://www.sustland.umn.edu/implemen...es/wall_i8.gif
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Old 03-26-2012, 04:22 PM   #4
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Retaining Wall Geogrid + landscape fabric?


The geogrid is there to increase the strength of the soil. In fact, with proper use of geogrid, the soil holds itself up, and the block is there for appearance and to prevent sloughing at the face, but amazingly is not actually needed to support the wall.

The filter fabric serves a completely different purpose. The filter fabric is installed to prevent migration of fine material into the gravel backfill you need to place behind the wall. The geogrid always takes precedence, in the sense that the geogrid is placed horizontally, and must extend in a continuous manner to the depth defined by the block manufacturer. Say the geogrid needs to extend four feet from the wall. This is likely to intersect the vertical filter fabric, so you simply cut the filter fabric into strips, which are installed between the geogrid layers.
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Old 03-26-2012, 04:44 PM   #5
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Retaining Wall Geogrid + landscape fabric?


That's what I was thinking if you see my first post under question 2, but my concern i; if I do strips of landscape fabric, wouldnt that just make the fabric pointless as water is going to bring dirt from in between the intersections (along the horizontal edges of the strips and the geogrid), into my gravel and drainpipe?

Am I over thinking this?? Ive been known to do that

Edit: I will just ask the place I am going to on Thursday. I am sure this is basic stuff that I just don't know. Thanks!!

Last edited by teamcampreder; 03-26-2012 at 04:51 PM.
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Old 03-26-2012, 06:03 PM   #6
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Retaining Wall Geogrid + landscape fabric?


Ask where you go, but you get very little soil movement through a narrow opening between strips. Relax, you have far bigger issues coming up.

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