Anchoring geogrid to segmental blocks
Anchoring geogrid to segmental blocks
(OP)
There is a low bid here for a 14 foot high wall that is under the category of "segmental block wall MSE type". The blocks will be from a ready-mix plant where returned concrete is placed in forms with a rock-like face sides. There is a dimple in the bottom and a "bump" on the top. They measure 2x2x8 ft. The claim is the concrete strength is 3,500 psi. That is not the problem, even if it is weak concrete, the blocks do stack on top of each other OK and there will be a tilt back.
They work fine for small height walls, but this job will need geogrid reinforcing. Contractor's design engineer is struggling with how to secure the geogrid placed between each course of blocks. The geogrid type has yet to be selected. Backfill is clean fine sand.
Is simple friction enuff?
Any ideas for how to make the attachment will be helpful.
I'm the owner's engineer, but would like to suggest some ways to do this to get the job done right.
They work fine for small height walls, but this job will need geogrid reinforcing. Contractor's design engineer is struggling with how to secure the geogrid placed between each course of blocks. The geogrid type has yet to be selected. Backfill is clean fine sand.
Is simple friction enuff?
Any ideas for how to make the attachment will be helpful.
I'm the owner's engineer, but would like to suggest some ways to do this to get the job done right.





RE: Anchoring geogrid to segmental blocks
Meeting unit strength and density requirements is no problem, even for "come-back" concrete. Unfortunately, some people buy some off-the-shelf forms for a product that cannot be used for engineering appications because the design of the unit shape has no documentation. Many units are purely designed to be used for gravity walls, and engineering applications are convenient and incidental.
Pure surface friction is not enough. You have to deal with rotation of the units, surface cleanliness and moisture. Usually, a great deal of distortion over a large area is the key to developing the strength of the geo-grid.
Dick
RE: Anchoring geogrid to segmental blocks
If further is needed, what about adding a piece of #3 bar threaded between the mesh on the far side of the lugs?
Mike McCann
MMC Engineering
RE: Anchoring geogrid to segmental blocks
Localized attachement by isolated pins or "knobs" lead to localiazed load concentrations and a "zipper" failure of the geo-grid fabric. Full scale tests or real life examples of actual installations are required to get away from the theoretic or microscopic analysis.
Individual locking lugs are not equal to a uniformly installed geo-grid connection. Poor setting of one 3-4' block can easily lead to rotation, shear or other load concentration.
You need documentation of the performance of the individual units used with geo-grid.
RE: Anchoring geogrid to segmental blocks
RE: Anchoring geogrid to segmental blocks
Normally, these block are a secondary product made by a ready-mix producer to use the small amount of return concrete or to keep people busy when it rains. They are fine for low gravity walls, but they are really not made by a 'concrete block producer" (SRW mfgr.). Anything greater will require documentation of product performance regarding the ability to develop the real anchorage of the geo-grid to the wall face under the typical conditions (creep, moisture, friction reducing sand, etc.).
Any responsible material supplier should be able to provide an engineer with documentation of the product performnce in an engineered wall. If the contractor's engineer is "struggling" for a method to attach the block to the necessary geo-grid, that presents a question about the reliability of the system. If you make any changes in the ready-mix block producers product, you will be responsible/liable fo the results.
Since it is a relatively low(14') engineered wall, it may be prudent to seek out the smaller units (there are many SRW U.S. company products that are used both domestically and intenationally) that have a proven track record of walls over 40'. I am sure the local municipal engineering departments/DOT have some guidlelines for the smaller units since they are frequently use them for similar applications.
Dick
RE: Anchoring geogrid to segmental blocks
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