Bedrock epoxy anchors for load transfer of embeds in tension.

[diegotorres2020]

I'm looking for information in regards to the design of bedrock embed anchors for a project. The bedrock anchors are connecting to a footing which supports a pre-cast shear wall. The footings can't get any bigger to help support the overturning effect of the shear wall, so I am trying to tie down the footing down to bedrock using embed anchors. I ran into literature from "Williams Form engineering Corp" but nothing else major comes out on the web, and the info from Williams seems to be only for their products and not very descriptive of the actual design of the anchors capacity. I'm wondering if anyone has nay useful resources or where i can get better design information on bedrock embeds. TIA

 

[WARose]

The army provides one method in one of their EM manuals (see Chapter 9):

https://www.publications.usace.army.mil/Portals/76/Publications/EngineerManuals/EM_1110-1-2908.pdf

Whatever you do.....I'd clear it [the method & variables] with a geotech. Whenever I've anchored to/sat on bedrock....what I have thought the RQD was and what they thought the RQD was......was typically pretty far apart. (Just like we sometimes disagree with them on allowable bearing pressure and so forth.)

 

[dik]

Rock Quality Designation (RQD) is a measure of quality of rock core taken from a borehole.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[WARose]

Rock Quality Designation (RQD) is a measure of quality of rock core taken from a borehole.

But that gets adjusted sometimes just like SPT data. So that's what I am getting at: the judgement of a geotech is needed with this.

 

[diegotorres2020]

Thanks so much for the input. We're waiting for the geotec to advice and move forward. I just wanted to get ahead and see if there is anything we can ballpark before waiting for the geotec.

 

[bugbus]

We would normally check for (1) shaft adhesion failure and (2) cone pull-out.

For grouted anchors we often refer to BS 8081 (1989) which gives an ultimate shaft adhesion between grout and rock equal to 10% of the unconfined compressive strength of the rock, up to a maximum of 4 MPa. For the bar-grout interface, they suggest 2 MPa ultimate resistance for a deformed/threaded bar, based on a minimum 30 MPa cementitious grout. Epoxy grout would probably give you better strength.

Then the potential cone pull-out needs to have enough weight to resist any uplift. This is normally based on a 90 degree angle (if I remember right) for medium strength rock. Smaller angle for weaker rock, larger angle for stronger rock.