Modular Block Wall With Geogrid Into Bedrock

[JohnTerry4]

I am designing a Mechnically Stabilized Earth Wall Using modular blocks and geogrid reinforcement. Bedrock may be encountered during excavation for the geogrid which would hinder from achieving the required geogrid embedment lengths during construction.

Is there a recommended way to anchor the geogrid into the bedrock (it is sound, igneous bedrock) in lieu of chipping bedrock to achieve the required geogrid length? Does anyone have a detail to share?

TYVMIA

 

[emmgjld]

A dimension diagram, giving a section above and below the wall, with notes regarding geology and existing/worse case groundwater is required.

 

[EireChch]

I cant see why drilling and grouting a hook into the rock isnt possible. Its unusual but can be designed and detailed properly . You could go down the other route in assessing reduced pressures due to the presence of rock within you Ka wedge.

 

[LOTE]

If global stability and seismic will allow it and you have fully stable bedrock, you can reduce your grid lengths as low as 0.3*H. NHI/FHWA has a great guide on Shored MSE (SMSE) walls:
FHWA SMSE

If you are reducing below the typical lengths (<0.6*H), I typically lap geogrid up along the rock face (or other surface), then lap it back 3 ft when you get to the elevation of the next course. Leave 3" of fill between the geogrid lap and next geogrid course. Similar to the face at a temporary welded wire faced MSE wall (checkout Strata or Mirafi details for this).

 

[JAE]

Under normal circumstances, you are anchoring the geogrid with earth that "grabs" it everywhere.

If you pin it to rock at a discreet point you would be potentially introducing higher, concentrated forces on single points in the geogrid, which would result in local tears or other failures.

I'd be sure to check with the geogrid manufacturer before pinching their material at singular points vs. uniform earth embedment.

 

[LOTE]

Under normal circumstances, you are anchoring the geogrid with earth that "grabs" it everywhere.

If you pin it to rock at a discreet point you would be potentially introducing higher, concentrated forces on single points in the geogrid, which would result in local tears or other failures.

I'd be sure to check with the geogrid manufacturer before pinching their material at singular points vs. uniform earth embedment.

Agreed, pins would be a bad idea.

If external/global stability allows it, I recommend wrapping along the rock face like this:


And if external/global does not allow it, anchors should be attached to a pipe and the geogrid wrapped around the pipe like this (substitute concrete anchors for rock anchors) to avoid those point loads: