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Can someone explain Geogrid!?

Discussion in 'Landscape Architecture and Design' started by drsogr, Sep 17, 2004.

  1. drsogr

    drsogr LawnSite Bronze Member
    Posts: 1,275

    I need help, I have never installed a retaining wall over 2' and everyone says that you need geo grid, once you get to the taller walls. My question is, what is geogrid? Whats it made out of? When do you need it? What kind of expertise do you need to use it? I know I should probably know what it is, but I have never used it. Teach me the way!
  2. Bull

    Bull LawnSite Senior Member
    from NC
    Posts: 308

    GeoGrid is a material that goes between two layers of block and extends back into the backfill area behind the wall. You can go to some of the websites (Keystone or Mesa Block) for the block manufacturers and see examples of it and based on their specifications determine when it is needed. It serves the same purpose in a block wall as a deadman serves in a timber wall.
  3. D Felix

    D Felix LawnSite Bronze Member
    Posts: 1,898

    I'll add to what Bull said...

    Geo-grid is a soil re-inforcement that helps to stabilize an SRW (segmented retaining wall). As Bull said, it extends back into the soil behind the wall, and basically creates (depending on a lot of factors) a 4-10 stabilized mass of earth that retains the hillside.

    Some walls can be built purely as "gravity" walls, with no re-inforcement. I think the maximum a Keystone wall can be built is ~4', depending on soil conditions. Versa-lok Mosaid is around 3'. Different manufacturers have different specifications for using geo-grid. A lot of it depends on soil conditions, the grade above the wall, and surcharge on the wall.

    A lot of guys on here will tell you that anything over 4' needs to be engineered. While that may be (legally) the case in some or most areas, it may or may not be in yours. I highly doubt that is the case here in our county based on previous experience with other things, so we don't worry about it. What we do, however, is make d*mn sure that the wall is put in to meet the specifications of the manufacturer, or to exceed them. So far, we haven't had to build a wall over 5-6' in hieght, but I would think that much over 8 and we probably would be looking for an engineer anyway. We are meeting with a manufacturer rep on Monday about the wall that we are going to be starting soon, most manufacturers have reps in most areas that are capable of psuedo-engineering a wall if need be.

    Anyway, if you need more info, try a search. I think grid was covered a month or two ago, possibly in more depth than I just did...


  4. drsogr

    drsogr LawnSite Bronze Member
    Posts: 1,275

    Thanks guys for all the help. Now I have more questions, what does geogrid look like...is it like a spike with a hook on it? Does anyone have a picture or something? Is it metal or plastic? I am sure the first tall wall I do, I will learn quickly, but I am not for sure when that will be. So I just want to get a grasp on what it is, so I know what you guys are talking about.

  5. GreenMonster

    GreenMonster LawnSite Silver Member
    from NH
    Posts: 2,702

    Hey Jayhawk,

    Here's a link from the Allan Block website:


    Geogrid is a "synthetic" mesh sheet. It comes in rolls, (varying lengths), 3' or 4' wide. It looks like....., well....., grid. I can be easily cut with a razor knife.

    This attachment has another pic too. Hopefully the attachment works.
  6. GreenMonster

    GreenMonster LawnSite Silver Member
    from NH
    Posts: 2,702

    well, attachment DIDN'T work. web page ain't a valid attachment.

    anyway, here is another pic, well, illustration anyhow. these are now coming in 50' rolls (so says the website).

    Geogrid white364.jpg
  7. drsogr

    drsogr LawnSite Bronze Member
    Posts: 1,275

    Thanks guys for your help, I know this has to sounds like a pretty dumb thread! So you put this grid in between each layer of blocks and back into the soil. Do you have to attach the grid to the blocks? I would assume that when using this you would have to also back fill in between each layer? Thanks for all the help!
  8. MarcusLndscp

    MarcusLndscp LawnSite Senior Member
    Posts: 634

    Someone once explained GeoGrid to me this way-
    Take a small quantity of sand, say a 5 gal bucket full, empty it on a table and put one wall block on top of it what would it do? That pile of sand would compress down quite a bit because of all the weight on it.....the sides of the sand are not stable enough to support the weight.
    Next take a handful of sand and kind of spread it around and put a coffee filter on top of it. Then another thin layer of sand and another filter and then more sand and another filter etc. After a few layers put a block on top of your stack of filters and sand. This pile should better support the weight of the block on top.......thus the sides of each layer of sand won't be pushing out and causing the pile to compress.
    Now imagine a wall around these piles. Without the filters ,or geogrid, your backfill would push against your wall much more causing the wall to fail. With the filters or geogrid, each layer of backfill is more supported upon the next thus reducing the amount of force pushing outwards.
    Just a different way to think about it other than a deadman or tieback (that is if what I just typed made any sense what so ever!!!???). I thought it was pretty cool anyways.
    Take care
  9. drsogr

    drsogr LawnSite Bronze Member
    Posts: 1,275

    Thanks that does help out...I was thinking of geogrid as more of something to tie the blocks into the ground, than something to disperse the weight.
  10. Lanelle

    Lanelle LawnSite Bronze Member
    Posts: 1,361

    I would describe the action of the geo-grid as follows: The downward force of the backfill on the layers of geo-grid is greater than the lateral force against the back of the wall, thus the grid helps to keep the wall vertical and resisting the pressure to move forward. It is also very important to use clean gravel behind the wall and drainage pipe to carry away the water that would exert force against the wall. There are several types of grid and each has to be installed according to the manufacturers directions or engineer's specfications.
    A good manufacturer's rep will be able to go through the details with you and should give you a product design manual so you can see how to properly install all the elements of the wall. It is very important to know the type of soils that you will be dealing with so you don't start off with an unstable site.
    Best wishes for a great project.

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