What is Geogrid?

Discussion in 'Landscape Architecture and Design' started by studentlawn, Jul 22, 2004.

  1. studentlawn

    studentlawn LawnSite Member
    Messages: 117

    Im new to the realm of landscape installation so I have been reading all posts lately to in an attempt to absorb some information. I keep reading about two things which have been keeping me confused. Every time a subject on a wall comes up, the use of geogrid comes into question. I am not quite sure what is it, so I was hoping someone would clear that up for me. Also, the phrase "that wall needs to be engineered". My best assumption was that an architect needs to test it out in CAD, but thats only a guess. So I was hoping someone could clear these two things up.
  2. kris

    kris LawnSite Bronze Member
    from nowhere
    Messages: 1,578

    Geogrids are flexible, synthetic meshes that are manufactured specifically to reinforce the soil mass behind segmented retaining walls.... This provides slope stabilization and earth retention. The use of geogrid for slope stabilization allows retaining walls to perform to 30 feet or more...... There are a variety of sizes and strenths. All of them are rated for their strenth and ability to resist stretching or creeping....as the wall is built, layers of grid are placed at specific locations in the wall. The soil is compacted around grid layers, and the friction that develops, interlocks the soil and grid. As layers of geogrids are positioned within the soil mass and soil is compacted around them, the internal strength of the soil mass behind the wall resists overturning and sliding.

    ENGINEERED WALLS.....Site specific engineering drawings are recommended and can be usually arranged by contacting your dealer...Typical spacing is 2 to 3 feet between layers. The length of the geogrid can be as short as 3 feet (1 m) or in excess of 15 feet (5 m).

    Just got news today from our supplier...he told me that the usual recommended height of a wall that requires grid has now changed from 4 ft to 3 ft. ...guess we'll be putting more grid in.
  3. D Felix

    D Felix LawnSite Bronze Member
    Messages: 1,898

    Kris- is that across the board, or just for your area specifically?

    What kind of block do you predominatly use?

  4. AGLA

    AGLA LawnSite Bronze Member
    Messages: 1,776

    Most states require a Structural Engineer to design a wall of over 4'. Some states it is higher , some are lower. The engineer does not usually design the layout of the wall, but specifies how it is to be put together so that it does not fail. The whole reason for this is public safety.

    For a concrete retaining wall the engineer might specify how wide the footing should be, how deep, what thickness, what size rebar, the spacing and placement of the rebar, where on that footing the wall needs to be, size of a key way, thickness of the wall, specifications on the concrete mix, .....

    He really takes your design and gives it specifications to make sure that it is strong enough to fit the application. It is all to keep a wall from failing and killing someone in the process. If you build it to his specs and it fails, you are off the hook. If you wing it and it fails, you can be in very serious trouble.
  5. kris

    kris LawnSite Bronze Member
    from nowhere
    Messages: 1,578

    1) I don't know Dan ...next time I chat Ill ask

    2) Our block of choice the last few years has been Roman Pissa
  6. hoyboy

    hoyboy LawnSite Senior Member
    from Chicago
    Messages: 346

    I think it's some math class I missed back in high school....
  7. JimLewis

    JimLewis LawnSite Fanatic
    Messages: 6,872

    Kris pretty much answered your question correctly.

    Here is a picture of geogrid being used at the beginning of the creation of a retaining wall.....

    See Geogrid Here
  8. studentlawn

    studentlawn LawnSite Member
    Messages: 117

    That helps alot, so lets say im building a large wall, I install the geogrid against the cut area then backfill against the geogrid.

    Thanks Guys,

  9. JimLewis

    JimLewis LawnSite Fanatic
    Messages: 6,872

    Yah, basically. But it's a little more complex than that from what I gather.

    First of all, if you're using geogrid, you're probably also building a retaining wall that will require a geo-engineer's design. So he'll be directing the job details for you. But typically, they'll call for layers of geogrid ever few layers and they'll want the ground under each layer of geogrid to be very well compacted. The engineer will also direct you as to how far back from the wall the geogrid has to go, etc.
  10. Scag48

    Scag48 LawnSite Fanatic
    Messages: 6,067

    So based on the picture, you smash some of the geogrid right under a course of blocks? How does tend to work out with levelness of the blocks and such?

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