Grout to Rock Bond Strength 2

[dmitriy555]

I am working on the foundation reinforcement design that currently has a few rock anchors holding it in place, we need to add more micropiles (3" dia. DYWIDAG 150ksi bar). The original foundation drawing is pretty vague and does not have specs shown for the anchor rocks or the grout used, However the geo specifies working bond strength between rock-grout interface as 62psi. Do you think it is ok to assume the same bond strength for the proposed DYWIDAGs or it can be something higher? Does the bond depend on the type of the grout or rather the type and quality of the rock?
Thanks.

 

[molerat2210]

see FHWA-SA-97-070 Micropiles. Table 5-2

 

[Erdbau]

Bond almost entirely depends on the rock, as opposed to the grout. Grout should be specified at f'c > 3000psi. This should prevent any failures due to the grout.